CN114488519A - Diffraction optical lens with continuously adjustable large-angle incident focal length and design method thereof - Google Patents

Abstract

The invention discloses a diffraction optical lens with a continuously adjustable large-angle incident focal length and a design method thereof. Wherein the design method comprises: focusing linearly polarized incident light to a focal plane through the diffractive optical lens within an incidence angle +/-30 degrees as an optimization target to obtain optimized lens parameters; and obtaining the diffraction optical lens through a lens design model according to the optimized lens parameters. The design method disclosed by the invention is simple and efficient in process, the obtained diffractive optical lens is simple in structure and low in processing difficulty, the functions of continuously adjusting the focal length and expanding the field angle of the system can be realized simultaneously, and the application is efficient, flexible and accurate.

Description

Diffractive optical lens with continuously adjustable large-angle incident focal length and its design method

technical field

The present invention relates to the technical field of diffractive lenses.

Background technique

Currently, the widely used zoom technologies include optical zoom and digital zoom. The way to realize optical zoom is to add a mechanically movable lens group to the optical system. Therefore, in order to make the system have good zooming ability, it must have a large enough moving space, which also makes the traditional optical zoom system have disadvantages such as large volume, complex structure, high manufacturing cost, etc., and it is difficult to adapt to the miniaturization of the current optical system. , the need for integration; digital zoom is to use the influence processor or image processing software to separately enlarge the image obtained by a certain area in the photosensitive element, so as to give people the feeling of zoom, this simple partial enlargement does not really The focus changes in the sense, and because the area of the photosensitive element used becomes smaller, the image quality is worse than normal.

In recent years, with the development of diffractive optical devices, new ideas for optical system design have been brought. Diffractive optical structure is an ultra-thin structure using a dielectric material antenna with sub-wavelength characteristic size as a light wavefront modulator. After intensive research in recent years, diffractive optical structures have been used to solve many problems in traditional optical devices, such as chromatic aberration, monochromatic aberration, and adjustable focal length. However, these structures and designs have the disadvantages of complex structure, high difficulty in design and processing, and relatively single function.

For example, the mirror proposed by Chen Fei, Qiu Liangyu and others from the University of Rochester in the United States uses a flexible material polydimethylsiloxane (PDMS) as a substrate, on which electron beam etching and deposition methods are used. A unit structure of silver-silicon dioxide-silver is grown, and finally encapsulated with PDMS to form the final mirror. The mirror can change the position of the unit structure by stretching the PDMS substrate, thereby changing the phase distribution of the diffractive optical element, so as to realize the change of the focal length. However, it requires a three-layer structure, and the structure is very complex and the processing is very difficult. The substrate must be a transparent and flexible material, which requires strict wavelength and material requirements. At the same time, the stretching degree of the flexible material is very limited, and the focal length variation range is very limited; and the mirror Effective use requires normal incident light and cannot achieve large-angle focusing.

Another example is the achromatic lens with a large field of view proposed by Tang Dongliang of Hunan University and Zhang Xiaohu of Chongqing University, etc., which is designed by the method of optical design within a certain angle range. The phase of the red, green and blue) achromatic lens, and then grow titanium dioxide nano-columns on both sides of the glass substrate, and introduce the designed phase, so as to realize the function of achromatic achromatic with a large angle of view corresponding to the wavelength. Although the structure has only one substrate, the cell structure needs to be grown on both sides of the structure, and the processing operation is very difficult. After the processing is completed, the lens is easily damaged due to the exposure of the cell structure, which affects the effect. At the same time, the focal length of the lens is fixed and must be equal to The focal length of the optically designed achromatic lens cannot adapt to the working environment that requires a zoom lens.

As mentioned above, although with the development of modern optics, high integration and miniaturization are a major trend in the development of modern optical devices, especially in medical and civil fields such as AR and VR, lightness and compactness are a major requirement for optical systems. . Along with this trend, diffractive optical structures with small and thin as their outstanding advantages have a wide range of uses. However, the prior art still lacks an imaging system and a design method of a small-sized diffractive optical structure with a simple structure, low processing difficulty, a large angle of view and continuous zooming.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a design method of a diffractive optical lens that can simultaneously realize the functions of continuous focal length adjustment and expansion of the viewing angle of the system.

The present invention also aims to provide some specific diffractive optical lenses obtained by the above-mentioned design method.

The present invention first provides the following technical solutions:

A design method of a diffractive optical lens with continuously adjustable focal length of large angle incident, comprising:

Taking the linearly polarized incident light to be focused to the focal plane through the diffractive optical lens within the incident angle ±30° as the optimization goal, the optimized lens parameters are obtained;

According to the optimized lens parameters, the diffractive optical lens is obtained through a lens design model, wherein the lens design model includes:

The target lens includes two diffractive optical units with the central axes coinciding and the mutual rotation angle β taking the central axis as the axis and having diffractive optical structures on the surface, wherein 0<β<2π;

满足：The overall exit phase of the objective lens

Satisfy:

表示第一衍射光学单元的出射相位，

表示第二衍射光学单元的出射相位，h_l(r)表示通过下式获得的所述衍射光学透镜的的透镜曲面厚度：Among them, λ represents the wavelength of incident light, n ₀ represents the refractive index of air, H represents the overall thickness of the diffractive optical lens, n ₁ represents the refractive index of the material of the diffractive optical lens,

represents the exit phase of the first diffractive optical unit,

represents the exit phase of the second diffractive optical unit, and h _l (r) represents the lens surface thickness of the diffractive optical lens obtained by the following formula:

Among them, c represents the surface curvature radius of the diffractive optical lens, k and a _m represent the aspheric coefficient of the diffractive optical lens, m represents the order of the even-order aspheric surface of the diffractive optical lens, and r represents the polar coordinate Under the system, the distance between any point in the diffractive optical lens and the z-axis, wherein, the polar coordinate system is established with the center axis of the two diffractive optical units as the z-axis and the center of the first diffractive optical unit as the origin;

After the parallel light is incident, the respective outgoing phases of the two diffractive optical units of the target lens satisfy:

且

and

Among them, α represents the angle between the line connecting any point on the diffractive optical unit to the center and the polar axis in the polar coordinate system.

In the above process, the optimization can be realized by optical design software such as Zemax Optic Studio.

According to some preferred embodiments of the present invention, the optimization process includes:

S1 sets the incident light wavelength and multiple incident angles within ±30°, and sets the diffractive optical lens material and its front and rear surface profiles;

S2 sets the initial structural parameters of the diffractive optical lens, including its initial focal length, the initial radius of curvature of the front surface, the initial radius of curvature of the back surface, the initial distance between the front and rear surfaces, the initial aspheric coefficient of the front and rear surfaces, and its 2nd order , 4th order, 6th order, 8th order, 10th order initial parameters;

S3 is based on the initial structural parameters, and uses the corresponding obtained edge light height solution as the distance between the back surface and the image surface, and optimizes according to the optimization function, and obtains the optimized lens parameters after the focusing requirements are met.

According to some preferred embodiments of the present invention, the initial parameters of the 2nd order, 4th order, 6th order, 8th order and 10th order are set to 0.

According to some preferred embodiments of the present invention, the plurality of incident angles are respectively set to 0°, 5°, 10°, 15°, 20°, 25°, and 30°.

According to some preferred embodiments of the present invention, the lens material is set to be ZnSe.

According to some preferred embodiments of the present invention, the front and rear surfaces of the lens are set as even-order aspheric surfaces.

According to some preferred embodiments of the present invention, the optimization function is a root mean square wavefront difference function.

According to some preferred embodiments of the present invention, the lens design model further comprises: the diffractive optical unit has one or more of a stepped diffractive structure or a metasurface structure.

According to some preferred embodiments of the present invention, the lens design model further includes: the diffractive optical unit has a metasurface structure of a columnar array.

The present invention further provides a diffractive optical lens designed according to the above-mentioned design method, which has the characteristics of continuously adjustable focal length of large-angle incident, and its focal length is preferably 15.2 μm-9.9 μm.

According to some preferred embodiments of the present invention, the diffractive optical lens includes a first diffractive optical unit and a second diffractive optical unit that are placed relatively in parallel, and both the first diffractive optical unit and the second diffractive optical unit include a circle A flat plate substrate and a series of nanopillars grown on opposite sides of the substrate and perpendicular to the substrate, the substrates have a radius of 14 μm, a mutual distance of 100 nm, and a thickness of 1 μm. The heights are all 600 nm, the series of nano-pillars are arranged in the circumferential direction of polar coordinates with the center of the base as the origin, and the overall distribution covers a very long range of 0 to the base radius, a polar angle range of 0 to 2π, and From the origin to the outside, the adjacent circumferential nano-columns have different radii, and the spaced circumferential nano-columns have equal radii.

According to some preferred embodiments of the present invention, the diffractive optical lens includes a first diffractive optical unit and a second diffractive optical unit that are relatively parallel to each other, and both the first diffractive optical unit and the second diffractive optical unit have a circular outer surface The shape plane and the inner surface are all spiral staircase undulating structure, and the height distribution of each step is as follows:

表示透镜的出射相位，其中r表示该阶梯距离所述圆形平面的圆心的距离，λ表示入射光波长。where d represents the height of the ladder,

represents the outgoing phase of the lens, where r represents the distance of the step from the center of the circular plane, and λ represents the wavelength of the incident light.

The present invention has the following beneficial effects:

According to the design method of the present invention, an optical diffractive lens that realizes continuous focal length change in a large angle range can be obtained. In a specific application, the diffractive optical unit of the obtained lens is relatively rotated with its central axis as the axis, such as One diffractive optical unit remains unchanged, and the other diffractive optical unit rotates in the counterclockwise or clockwise direction, so that the incident light incident at a large angle can be focused on different focal planes after exiting.

The diffractive optical lens obtained by the design method of the present invention can greatly eliminate the monochromatic aberration, and at the same time, when the incident angle of the incident light reaches ±30° at the maximum, all the incident light can be well focused on the corresponding focal plane .

The diffractive optical lens actually obtained according to the design method of the present invention is efficient and fast in application, simple in structure and low in processing difficulty.

Description of drawings

FIG. 1 is a schematic diagram of the overall structure of the diffractive optical lens according to Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram of the surface structure of the diffractive optical unit according to Embodiment 1 of the present invention.

FIG. 3 is an effect diagram of phase distribution under different incident angles in Embodiment 1 of the present invention.

FIG. 4 is a schematic diagram of the outgoing phase and the summed phase distribution of the two diffractive optical units when β=1rad in Embodiment 1 of the present invention.

FIG. 5 is the electric field distribution of the transmitted far field of the lens in Embodiment 1 of the present invention when β=1rad.

FIG. 6 is the electric field distribution of the transmitted far field of the lens in Embodiment 1 of the present invention when β=1.2rad.

FIG. 7 is the electric field distribution of the transmitted far field of the lens in Embodiment 1 of the present invention when β=1.4rad.

FIG. 8 is a schematic diagram of the overall structure of the diffractive optical lens according to Embodiment 2 of the present invention.

FIG. 9 is the electric field distribution of the transmitted far field of the lens in Embodiment 2 of the present invention when β=1rad.

FIG. 10 is the electric field distribution of the transmitted far field of the lens in Embodiment 2 of the present invention when β=1.2rad.

FIG. 11 is the electric field distribution of the transmitted far field of the lens in Example 2 of the present invention when β=1.4rad.

Detailed ways

The present invention will be described in detail below with reference to the embodiments and drawings, but it should be understood that the embodiments and drawings are only used to describe the present invention by way of example, but do not limit the protection scope of the present invention. All reasonable transformations and combinations included within the scope of the inventive concept of the present invention fall into the protection scope of the present invention.

Example 1

According to the technical solution of the present invention, a specific diffractive optical lens structure is obtained through the following process:

The optical design software Zemax Optic Studio is used to optimize the design of the lens to obtain its specific phase. The optimization process includes:

The wavelength of the S1 incident light is set to 810nm, the incident angles are 0°, 5°, 10°, 15°, 20°, 25°, and 30°, respectively. All adopt even-order aspheric surfaces, and an aperture diaphragm with a diameter of 10 μm is set at a distance of 15 μm from the front surface;

S2 sets the initial parameters as follows: the radius of curvature of the front surface is 50μm, the radius of curvature of the rear surface is -50μm, the distance between the front and rear surfaces (ie the lens thickness H) is 10μm, and the distance between the rear surface and the image surface (ie the actual focal length f) is 15μm, and the aspheric coefficients and the 2nd, 4th, 6th, 8th, and 10th order parameters of the front and rear surfaces are set to 0;

The solution conditions for the variables set by S3 are as follows. The distance between the rear surface and the image surface is set as the edge ray height solution. The curvature radius of the front and rear surfaces, the distance between the front and rear surfaces, the aspheric coefficient, and the 4th, 6th, 8th, and 10th order parameters are all set to variable;

S4 sets the optimization function as follows. The default evaluation function adopts the RMS wavefront with 3 rings and 6 arms. The spherical aberration, coma and astigmatism are all set to 0, and the effective focal length is set to 15μm;

S5 Click "Tools" - "Optimize" to optimize the parameters set as variables above, open "Scatter Graph" to observe the focusing of the image surface, and repeat the optimization to make the scatter points as small as possible to obtain the final optimization result.

The obtained optimized parameters include: the optimized focal length is 15.21 μm, the curvature radius of the first surface c=1/0.042063 (mm ^-1 ), the aspherical surface parameter k=-1.046556, the aspherical surface coefficient a2=-9694.283695, the non-spherical surface Spherical coefficient a3=-1.883979×10 ⁸ , aspheric coefficient a4=6.180475×10 ¹¹ , aspheric coefficient a5=-2.282475×10 ¹³ ; the second surface: curvature radius c=-1/0.05356(mm ^-1 ), Aspheric parameter k=-3.90567, aspheric coefficient a2=-9480.947625, aspheric coefficient a3=-1.883979×10 ⁷ , aspheric coefficient a4=-8.44613×10 ¹⁰ , aspheric coefficient a5=-9.964269×10 ¹⁴ ; lens Thickness H=9.7 μm.

及透镜曲面厚度h_l(r)，代入设计模型，具体得到的一种由具有超颖表面结构的光学单元组成的衍射光学透镜，如附图1所示，该衍射光学透镜包括均由一个圆形平板基底和在基底一侧生长的垂直于基底的一系列纳米柱组成的第一衍射光学单元1和第二衍射光学单元2，且第一衍射光学单元1和第二衍射光学单元2的两片基底平行放置，纳米柱在两片基底相对面之间，第一衍射光学单元1和第二衍射光学单元2的半径r均为14μm，相互间的距离d＝100nm，其基底厚度均为1μm，纳米柱高度均为600nm，纳米柱分布如附图2所示，其以基底中心为原点按极坐标周向排列、且整体分布涵盖的极长范围为0～基底半径，极角范围为0～2π，纳米柱的位相范围覆盖0～2π。Under the above optimized parameters, the corresponding outgoing phase is obtained

And the lens surface thickness h _l (r), substitute into the design model, a kind of diffractive optical lens that is made up of the optical unit with the metasurface structure specifically obtained, as shown in accompanying drawing 1, this diffractive optical lens includes all by a circle The first diffractive optical unit 1 and the second diffractive optical unit 2 are composed of a flat plate substrate and a series of nano-pillars grown on one side of the substrate perpendicular to the substrate, and the two diffractive optical units 1 and 2 The substrates are placed in parallel, the nano-columns are between the opposite surfaces of the two substrates, the radius r of the first diffractive optical unit 1 and the second diffractive optical unit 2 are both 14 μm, the distance between them is d=100 nm, and the thicknesses of the substrates are both 1 μm. , the heights of the nanopillars are all 600 nm, and the nanopillars are distributed as shown in Figure 2. They are arranged in the circumferential direction of polar coordinates with the center of the substrate as the origin, and the extremely long range covered by the overall distribution is 0 to the radius of the substrate, and the polar angle range is 0 ~2π, the phase range of the nanopillars covers 0～2π.

在不同入射角及旋转角情况下的在x-z平面和x-y平面上的远场电场分布情况，如附图5-7所示，其旋转角依次为β＝1rad、β＝1.2rad和β＝1.4rad。The above-mentioned diffractive optical lens was simulated and tested in the full vector simulation software FDTD (Lumerical Solution). The substrates of the two diffractive optical units were made of SiO ₂ (Glass)-Palik, the radius was set to 14 μm, and the thickness was set to 1 μm. The nano-pillars on the two diffractive optical units use a-Si as the material. The radius is obtained by interpolation according to the phase obtained by optical design and the corresponding relationship between the column radius and the introduction position obtained by scanning. The height of the nano-pillars is 600nm, and the distribution is as shown in Figure 2. As shown, set the FDTD simulation area, select the range where the nano-columns are located, set the mesh, the precision is 40nm, the incident light is set to linearly polarized light with different incident angles θ with a wavelength of 810nm, and a monitor is set at 100nm behind the entire structure, and the incident light is set to 100nm. The light is linearly polarized light with a wavelength of 810 nm, and the two-layer diffractive optical unit takes its own longitudinal central axis as the rotation axis to rotate at a rotation angle of β, and the lens output phase distribution under different incident angles θ as shown in Figure 3 can be obtained. The effect diagram, and the effect diagram of the outgoing phase distribution under different rotation angles β as shown in accompanying drawing 4, further, obtained by the Kirchhoff diffraction integral formula

The distribution of the far-field electric field on the xz plane and the xy plane under different incident angles and rotation angles, as shown in Figure 5-7, the rotation angles are β=1rad, β=1.2rad and β=1.4 rad.

The above results show that when the incident angle θ is 0°, 10°, 20° and 30°, the incident light can be well focused at the focal plane 15.21 μm away from the exit surface.

此时没有聚焦效果，当其中一个衍射光学单元，如第二衍射光学单元2具有一定旋转角时，即β>0时，此时

有聚焦效果，当β的值不同时，焦距不同，说明其可实现连续焦距调节效果。When the rotation angle β is 0°, the exit phase of the entire lens is

At this time, there is no focusing effect. When one of the diffractive optical units, such as the second diffractive optical unit 2, has a certain rotation angle, that is, when β>0, then

There is a focusing effect. When the value of β is different, the focal length is different, indicating that it can achieve continuous focal length adjustment effect.

As the value of β changes from 1rad to 1.2rad, and then to 1.4rad, the focal lengths of the lens system are 15.21 μm, 11.55 μm and 9.896 μm, respectively, showing a decreasing trend, which proves the continuous change of the focal length of the lens. At the same time, it can be seen from the simulation results that when the β value is fixed and the incident angle θ varies within the range of ±30°, there is no monochromatic aberration on the focal plane, and the focus is still very good, which proves that the The lens can correct the monochromatic aberration very well while the focal length changes continuously.

Example 2

The optimized lens parameters are obtained in the same way as in Example 1, and the initial parameters are adjusted as the radius of curvature of the front surface is 5mm, the radius of curvature of the rear surface is -5mm, and the distance between the front and rear surfaces (ie the lens thickness H) is 1mm , the distance between the rear surface and the image surface (that is, the actual focal length f) is 15mm, and the other parameters remain unchanged. The optimization function corresponds to it, changing the effective focal length to 15mm, and the optimized parameters are: curvature radius c=1/44.514 (mm-1), aspherical parameter k=2.688699, aspherical coefficient a2=-8.526631× ^10-5 , aspherical coefficient a3=6.33103× ^10-4 , aspherical coefficient a4=-2.332903× ^10-5 , aspherical The coefficient a5=--2.038745×10 ^-4 ; the second surface: the radius of curvature c=-1/50.12889(mm ^-1 ), the aspheric surface parameter k=-61.490765, the aspheric surface coefficient a2=-8.942814×10 ^-4 , Aspheric coefficient a3=6.875003×10 ^-4 , aspheric coefficient a4=-1.76955×10 ^-6 , aspheric coefficient a5=--1.135695×10 ^-4 ; lens thickness H=14.48465mm.

According to the above parameters, a diffractive optical lens composed of optical units with a stepped diffractive structure specifically obtained in this embodiment, as shown in FIG. 8 , the diffractive optical lens includes a circular plane on the outer surface and a The first diffractive optical unit 1 and the second diffractive optical unit 2 are placed opposite to each other in a spiral staircase, and the height distribution of each step is as follows:

Afterwards, the diffractive optical lens is simulated and tested through a process similar to that of Example 1, including first creating two matrices representing the phases of the two-layer stepped diffractive optical element, and then calculating the phase at each position in the matrix according to the phase extraction formula. Value and fill in (here, the angle can be changed by transforming the coordinates), superimpose the two to get a combined phase (that is, the phase of the exit plane), and finally write a diffraction algorithm based on Huygens' principle to bring in the obtained phase Perform calculations to obtain the far-field electric field distributions on the x-z plane and x-y plane under different incident angles and rotation angles, as shown in Figure 9-11, the rotation angles are β=1rad, β=1.2rad and β =1.4rad.

The results show that as the value of β changes from 1rad to 1.2rad, and then to 1.4rad, the focal lengths of the lens system are 14.15mm, 10.9mm and 9.2mm, respectively, which also show a decreasing trend, which proves that the stepped diffractive optical element Continuously tunable functions can also be achieved and the range of cell sizes can be extended from micrometers to millimeters.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All the technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, improvements and modifications without departing from the principles of the present invention should also be regarded as the protection scope of the present invention.

Claims (10)

1. The design method of the continuously adjustable diffractive optical lens of large angle incident focal length is characterized in that: it comprises: Taking the linearly polarized incident light to be focused to the focal plane through the diffractive optical lens within the incident angle ±30° as the optimization goal, the optimized lens parameters are obtained; According to the optimized lens parameters, the diffractive optical lens is obtained through a lens design model, wherein the lens design model includes: The target lens includes two diffractive optical units with the central axes coinciding and the mutual rotation angle β taking the central axis as the axis and having diffractive optical structures on the surface, wherein 0<β<2π; The overall exit phase of the objective lens

Satisfy:

Among them, λ represents the wavelength of incident light, n ₀ represents the refractive index of air, H represents the overall thickness of the diffractive optical lens, n ₁ represents the refractive index of the material of the diffractive optical lens, and h _l (r) represents the value obtained by the following formula The lens surface thickness of the diffractive optical lens:

Among them, c represents the surface curvature radius of the diffractive optical lens, k and a _m represent the aspheric coefficient of the diffractive optical lens, m represents the order of the even-order aspheric surface of the diffractive optical lens, and r represents the polar coordinate Under the system, the distance between any point in the diffractive optical lens and the z-axis, wherein, the polar coordinate system is established with the center axis of the two diffractive optical units as the z-axis and the center of the first diffractive optical unit as the origin; After the parallel light is incident, the respective outgoing phases of the two diffractive optical units of the target lens satisfy:

and

in,

represents the exit phase of the first diffractive optical unit,

represents the output phase of the second diffractive optical unit, and α represents the angle between the line connecting any point on the diffractive optical unit to the center and the polar axis in the polar coordinate system. 2. The design method according to claim 1, wherein the optimization process comprises: S1 sets the incident light wavelength and multiple incident angles within ±30°, and sets the diffractive optical lens material and its front and rear surface profiles; S2 sets the initial structural parameters of the diffractive optical lens, including its initial focal length, the initial radius of curvature of the front surface, the initial radius of curvature of the back surface, the initial distance between the front and rear surfaces, the initial aspheric coefficient of the front and rear surfaces, and its 2nd order , 4th order, 6th order, 8th order, 10th order initial parameters; S3 is based on the initial structural parameters, and uses the corresponding obtained edge light height solution as the distance between the back surface and the image surface, and optimizes according to the optimization function, and obtains the optimized lens parameters after the focusing requirements are met. 3 . The design method according to claim 2 , wherein: the initial parameters of the 2nd order, 4th order, 6th order, 8th order and 10th order are set to 0; and/or, the multiple incident angles Set to 0°, 5°, 10°, 15°, 20°, 25°, 30°, respectively. 4 . The design method according to claim 2 , wherein: the lens material is set to be ZnSe; and/or the surface shape of the front and rear surfaces thereof is set to be an even-order aspheric surface. 5 . 5 . The design method according to claim 2 , wherein the optimization function is a root mean square wavefront difference function. 6 . 6 . The design method according to claim 2 , wherein the lens design model further comprises: the diffractive optical unit has one or more of a stepped diffractive structure or a metasurface structure. 7 . 7 . The design method according to claim 2 , wherein the lens design model further comprises: the diffractive optical unit has a metasurface structure of a columnar array. 8 . 8. The diffractive optical lens designed according to the design method of any one of claims 1-7. 9 . The diffractive optical lens according to claim 8 , wherein the diffractive optical lens comprises a first diffractive optical unit and a second diffractive optical unit placed relatively in parallel, the first diffractive optical unit and the second diffractive optical unit Each unit includes a circular flat substrate and a series of nano-pillars grown on opposite sides of the substrate and perpendicular to the substrate, the substrates are all 14 μm in radius, 100 nm in distance from each other, and 1 μm in thickness, The heights of the nano-pillars are all 600 nm, and the series of nano-pillars are circumferentially arranged in polar coordinates with the center of the base as the origin, and their overall distribution covers an extremely long range of 0 to the base radius, and a polar angle range of 0-2π, and from the origin to the outside, the nano-columns in the adjacent circumferential directions have different radii, and the nano-columns in the spaced circumferential directions have the same radius. 10 . The diffractive optical lens according to claim 8 , wherein the diffractive optical lens comprises a first diffractive optical unit and a second diffractive optical unit placed relatively in parallel, the first diffractive optical unit and the second diffractive optical unit 11 . The units are all structures with a circular plane on the outer surface and a spiral staircase on the inner surface. The height distribution of each step is as follows:

where d represents the height of the ladder,

represents the outgoing phase of the lens, where r represents the distance of the step from the center of the circular plane, and λ represents the wavelength of the incident light.

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