CN109061780B - Dual-wavelength coaxial independent focusing super-surface lens - Google Patents

Abstract

The invention relates to the field of nano optics, in particular to a dual-wavelength coaxial independently-focused super-surface lens, which comprises: a substrate and a nanostructured cuboid. Dividing one side surface of the substrate into square unit grids, equally dividing the square unit grids into four small squares, and processing nano-structure cuboids with the same size at the centers of the two small squares on the same diagonal line; the nano-structure cuboid is rotated by a corresponding angle to modulate the phase of incident light corresponding to the nano-structure cuboid. The dual-wavelength coaxial independently-focused super-surface lens has the advantages of small size, thin thickness, light weight, small aberration and high integration level, the performance of the lens is superior to that of the combination of the existing high-quality objective lens and a phase modulation element, and the lens can be applied to stimulated emission dissipation super-resolution fluorescence imaging.

Description

A dual-wavelength coaxial and independent focusing metasurface lens

technical field

The invention relates to the field of nano optics, in particular to a dual-wavelength coaxial and independent focusing metasurface lens.

Background technique

The various aberrations and chromatic aberrations of modern high-quality objective lenses are well corrected, but the usual correction is applied to a relatively wide wavelength band, and it is impossible to correct very thoroughly. In addition, the objective lens is composed of many single glass lenses, so it is difficult to reduce the volume and weight, and many applications require fast nano-positioning and scanning of the objective lens. Larger objective lenses are not conducive to electronic servo system control. Quickly locate and scan. Therefore, the miniaturization of the objective lens focusing system is an important subject of scientific significance.

The focusing process of the objective lens to the laser is realized by the change of the refractive index and thickness of the lens material, which is essentially the modulation of the beam phase by the objective lens. Artificial microstructured materials or metasurface materials made by modern micromachining technology can modulate the phase, polarization and intensity of light respectively, and can theoretically design and process specific wavelengths, thus providing a new way of beam focusing. The metasurface lens is the micro-nano optical element that realizes this function.

The size, shape, orientation, and material of the microstructural units of a metasurface lens are usually determined by the laser wavelength and the desired tuning purpose. When the purpose of regulation is relatively simple, the structure of the microstructural unit is relatively simple, and basically corresponds to the laser wavelength. But for dual-wavelength laser regulation, if the purpose of regulation is different, the microstructural unit is more complicated.

Supramolecular building blocks are a new type of metasurface material suitable for independent regulation of multiple wavelengths. At present, there is no metasurface lens that utilizes supramolecular building blocks to achieve independent regulation and focusing of dual wavelengths.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a dual-wavelength coaxial and independent focusing metasurface lens for the above problems.

The embodiments of the present invention are implemented in this way, a dual-wavelength coaxial and independent focusing metasurface lens, including a substrate and a nanostructure cuboid;

One side of the substrate is divided into a square unit grid, and the square unit grid is equally divided into four small squares, and a kind of same size is placed in the center of the two small squares on the first diagonal line. Nanostructure cuboid, place another nanostructure cuboid with the same size in the center of the other two small squares on the second diagonal; rotate one of the nanostructure cuboid with the same size by a corresponding angle to modulate the corresponding is the phase of the incident light, and another nanostructured cuboid with the same size is rotated by the corresponding angle to modulate the phase of the other corresponding incident light; the corresponding angle is determined by the following formula:

where θ is the rotation angle of the nanostructured cuboid at (x, y) with the bottom center at (x, y), φ(x, y) is the additional phase modulation value of the incident light at (x, y), f, λ are the corresponding nanostructured cuboids of the same size The focal length and wavelength of the incident light.

The embodiment of the present invention provides a dual-wavelength coaxial and independent focusing metasurface lens. By dividing one side of the substrate into a square unit grid, and then dividing the square unit grid into four small squares, Nanostructured cuboids with the same size are placed in the centers of two small squares on the same diagonal; the nanostructured cuboids are rotated by a corresponding angle to modulate the phase of the corresponding incident light. The dual-wavelength coaxial and independent focusing metasurface lens of the invention has small size, thin thickness, light weight, small aberration and high integration, and its performance can be superior to the combination of the existing high-quality objective lens and phase modulation element, and can be applied to Dissipative super-resolution fluorescence imaging for stimulated emission.

Description of drawings

1 is a schematic diagram of the layout of the rotation directions of different sizes of cuboids in a metasurface lens square unit grid with dual-wavelength coaxial and independent focusing provided by an embodiment of the present invention;

2 is a structural diagram of a metasurface lens with dual-wavelength coaxial independent focusing provided by an embodiment of the present invention;

3 is a schematic diagram of incident focusing of circularly polarized light with a dual-wavelength coaxial and independent focusing metasurface lens according to an embodiment of the present invention;

4 is a vortex phase distribution diagram obtained after phase modulation of a dual-wavelength coaxial and independently focused metasurface lens provided by an embodiment of the present invention;

5 is a spherical wave phase distribution diagram obtained after phase modulation of a dual-wavelength coaxial and independently focused metasurface lens provided by an embodiment of the present invention;

6 is a phase distribution diagram of a spherical wave superimposed vortex phase obtained by a dual-wavelength coaxial and independently focused metasurface lens phase modulation provided by an embodiment of the present invention;

7 is an annular light spot generated by focusing after circularly polarized light with wavelength λ ₁ is incident on a dual-wavelength coaxial and independently focused metasurface lens provided by an embodiment of the present invention;

FIG. 8 is a solid light spot generated by focusing circularly polarized light with wavelength λ ₂ into a dual-wavelength coaxial and independent focusing metasurface lens provided by an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings 1-8 and the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The embodiment of the present invention provides a dual-wavelength coaxial and independent focusing metasurface lens, which includes a substrate and a nanostructure cuboid;

As shown in FIG. 1, one side of the substrate is divided into a square unit grid, and then the square unit grid is equally divided into four small squares, at the center of the two small squares on the first diagonal line Place one nanostructure cuboids 1 and 3 (or 2 and 4) of the same size, and place another nanostructure cuboids 2 and 4 (or 1 and 3); rotate one of the nanostructure cuboids 1 and 3 (or 2 and 4) with the same size by a corresponding angle to modulate the phase of the incident light corresponding to it, and rotate the other nanostructure cuboids 2 with the same size and 4 (or 1 and 3) are rotated by a corresponding angle for modulating the phase of another incident light corresponding thereto; the corresponding angle is determined by:

where θ is the rotation angle of the nanostructured cuboid at (x, y) with the bottom center at (x, y), φ(x, y) is the additional phase modulation value of the incident light at (x, y), f, λ are the corresponding nanostructured cuboids of the same size The focal length and wavelength of the incident light;

The resulting lens structure is shown in FIG. 2 .

In an embodiment of the present invention, the nanostructured cuboid is made of TiO ₂ material. The function of the TiO ₂ cuboid is to modulate the phase of the incident light at the point by rotating the corresponding angle, and to realize the phase modulation of the incident light beam through the nanostructured cuboid array.

In an embodiment of the present invention, after the phase modulation of the dual-wavelength coaxial and independently focused metasurface lens, the two different wavelength beams are focused into the same or different shapes and are at the same or different positions on the axis. In the present invention, the two key points for adjusting the phase of the incident beam are the size of the nanostructured cuboids and their respective rotation angles. According to different desired results, the size of the nanostructured cuboids and the respective nanostructured cuboids can be adjusted accordingly. angle of rotation.

In an embodiment of the present invention, the size of the nanostructured cuboid is determined by parameter optimization and simulation by using the finite difference time domain method according to the diffraction efficiency of the dual-wavelength coaxial and independent focusing metasurface lens.

The embodiment of the present invention provides a dual-wavelength coaxial and independent focusing metasurface lens. By dividing one side of the substrate into a square unit grid, and then dividing the square unit grid into four small squares, Place a nanostructured cuboid with the same size in the center of two small squares on the same diagonal; rotate the nanostructured cuboid by a corresponding angle to modulate the phase of the corresponding incident light, forming two groups of units for modulating two The phases of the light of different wavelengths achieve independent focusing of the two wavelengths under the illumination of circularly polarized light. The working state is shown in FIG. 3 , the incident light beam 5 is incident from the smooth surface of the metasurface lens 6 that is coaxially focused independently with two wavelengths, and forms a focus 7 on the other surface. The dual-wavelength coaxial and independent focusing metasurface lens of the invention has small size, thin thickness, light weight, small aberration and high integration, and its performance can be superior to the combination of the existing high-quality objective lens and phase modulation element, and can be applied to Dissipative super-resolution fluorescence imaging for stimulated emission.

The manufacture of a dual-wavelength coaxial and independent focusing metasurface lens and the effect achieved are further described below with reference to an embodiment.

Step S1: according to the two different wavelengths of the incident circularly polarized light beam, two suitable nanostructured cuboids of different sizes are selected. In this embodiment, the wavelengths λ ₁ =473 nm, λ ₂ =633 nm, the length and width of the two nanostructured cuboids are l ₁ =90 nm, w ₁ =45 nm, l ₂ =145 nm; w ₂ =105 nm, the height of the cuboid is both h=320 nm.

Step S2: Divide one side of the substrate into a square unit grid, then divide the square unit grid into four small squares, and place nanometers of the same size in the centers of the two small squares on the same diagonal. Structural cuboid; the nanostructured cuboid is rotated by a corresponding angle to modulate the phase of the incident light corresponding to it and divided into a grid of square cells, and then each square cell is divided into four small squares, which are located on the first diagonal line. A nanostructured cuboid with the same size is placed in the center of the two small squares of , and another nanostructured cuboid with the same size is placed in the center of the other two small squares on the second diagonal. As shown in Fig. 1, 1 and 3, 2 and 4 respectively represent a group of nanostructured cuboids with the same size. The side length of the square structural unit is 420 nm, and the side length of the small square structural unit is 210 nm.

Step S3: use one of the nanostructured cuboids with the same size to rotate the angle _θ1 to modulate the phase _of the incident light of the corresponding wavelength λ1 where the small square structural unit is located, and rotate the other nanostructured cuboids with the same size by the angle _θ2 It is used to modulate the phase of the incident light of the corresponding wavelength λ ₂ where the small square structural unit is located. FIG. 2 is a schematic structural diagram of a dual-wavelength coaxial and independent focusing metasurface lens provided by an embodiment of the present invention, which is drawn by Matlab programming.

in,

The meaning of each parameter is the same as that in the previous embodiment.

After the phase modulation of the dual-wavelength coaxial and independent focusing metasurface lens, the two different wavelength beams are focused into different shapes, and can be at different positions on the axis or the same position on the axis.

(平面直角坐标系中某一直线与坐标X轴之间的夹角，从主轴起算，逆时针方向为正)。其工艺流程为：在光刻胶ZEP520上制作该超透镜，其中光刻胶厚度与纳米结构长方体高度320nm一致；然后利用原子层沉积技术在处理过的光刻胶上沉积一层厚度60nm左右TiO₂膜；光刻胶顶部的TiO₂膜用反应离子刻蚀法去除；最后剥离剩余电子束光刻胶。Step S4: The BMP format diagram of the electron beam lithography process as shown in FIG. 2 drawn by Matlab programming is fabricated into a meta-surface lens by using a general process. The nanostructured cuboid material of the metasurface lens is TiO ₂ , the base is SiO ₂ material, and the azimuth angle of rotation of a single nanostructured cuboid is

(The angle between a straight line in the plane rectangular coordinate system and the coordinate X axis, counted from the main axis, is positive in the counterclockwise direction). The technological process is as follows: the superlens is fabricated on the photoresist ZEP520, wherein the thickness of the photoresist is consistent with the height of the nanostructure cuboid, 320 nm; and then a layer of TiO with a thickness of about 60 nm is deposited on the treated photoresist by atomic layer deposition technology ₂ film; the _TiO2 film on top of the photoresist was removed by reactive ion etching; the remaining e-beam photoresist was finally stripped.

Step S5: Using the mechanical installation and adjustment mechanism, the laser beam emitted by the laser is installed together with the linear polarizer and the quarter glass to obtain circularly polarized light, the circularly polarized light is incident on the prepared two wavelengths with the same wavelength. Axis-independently focused metasurface lens with coaxial adjustment, alignment and fixation. As shown in Figure 3, the wavelengths of the two incident laser beams are 473 nm and 633 nm, respectively, and a coaxial annular spot and a solid spot are obtained in the focal area.

4 is a vortex phase distribution diagram obtained after phase modulation of a dual-wavelength coaxial and independently focused metasurface lens provided by an embodiment of the present invention;

5 is a spherical wave phase distribution diagram obtained after phase modulation of a dual-wavelength coaxial and independently focused metasurface lens provided by an embodiment of the present invention;

6 is a phase distribution diagram of a spherical wave superimposed on a vortex phase obtained by phase modulation of a dual-wavelength coaxial and independently focused metasurface lens provided by an embodiment of the present invention.

The structure diagram of a dual-wavelength coaxial and independent focusing metasurface lens shown in Figure 2 is imported into the finite difference time domain method FDTD software for simulation. Solid spot.

The invention directly combines the vortex phase modulation of the vortex phase plate with the topological charge of 1 and the spherical wave phase modulation of the objective lens, and is unifiedly completed by the sub-wavelength spacing nanostructure cuboid array metasurface lens. The dual-wavelength metasurface lens has high integration, the size is less than 1 mm, and the thickness is thin, which can be in the order of microns. The quality is particularly light, and the aberration and chromatic aberration are better than the existing high-quality objective lenses, so it is especially suitable for the miniaturization of equipment systems and rapid positioning and scanning.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the patent of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

It will be apparent to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, but that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments are to be regarded in all respects as illustrative and not restrictive, and the scope of the invention is to be defined by the appended claims rather than the foregoing description, which are therefore intended to fall within the scope of the claims. All changes within the meaning and scope of the equivalents of , are included in the present invention.

In addition, it should be understood that although this specification is described in terms of embodiments, not each embodiment only includes an independent technical solution, and this description in the specification is only for the sake of clarity, and those skilled in the art should take the specification as a whole , the technical solutions in each embodiment can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims (4)

1. a dual-wavelength coaxial independently focused metasurface lens, is characterized in that, comprising: substrate and nanostructure cuboid; One side of the substrate is divided into a square unit grid, and the square unit grid is equally divided into four small squares, and a kind of same size is placed in the center of the two small squares on the first diagonal line. Nanostructure cuboid, place another nanostructure cuboid with the same size in the center of the other two small squares on the second diagonal; rotate one of the nanostructure cuboid with the same size by a corresponding angle to modulate the corresponding is the phase of the incident light, and another nanostructured cuboid with the same size is rotated by the corresponding angle to modulate the phase of the other corresponding incident light; the corresponding angle is determined by the following formula:

where θ is the rotation angle of the nanostructured cuboid at (x, y) with the bottom center at (x, y), φ(x, y) is the additional phase modulation value of the incident light at (x, y), f, λ are the corresponding nanostructured cuboids of the same size The focal length and wavelength of the incident light. 2 . The dual-wavelength coaxial and independent focusing metasurface lens according to claim 1 , wherein the nanostructured cuboid is made of TiO ₂ material. 3 . 3. the metasurface lens of a kind of dual-wavelength coaxial independent focusing as claimed in claim 1, it is characterized in that, after the metasurface lens phase modulation of described dual-wavelength coaxial independent focusing, the light beams of two different wavelengths are focused. into the same or different shapes and in the same or different positions on the axis. 4. the metasurface lens of a kind of dual-wavelength coaxial independent focusing as claimed in claim 1, it is characterized in that, the size of described nanostructure cuboid is based on the metasurface lens diffraction efficiency of described dual-wavelength coaxial independent focusing, using The finite-difference time domain software is determined by parameter optimization and simulation.

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