Metasurface lens and its design method

Abstract

The present application discloses a metasurface lens and its design method. Based on the present application, each unit structure in the unit structure array of the metasurface lens has a four-quadrant symmetry structure feature, so that the metasurface lens is configured as a polarization-insensitive lens. Moreover, the four-quadrant symmetry structure features of the unit structures in the unit structure array are not all the same, and the characteristic sizes of the unit structures with the same four-quadrant symmetry structure feature in the unit structure array are not all the same, which can help improve the coverage ability of the reference phase and compensation phase of each unit structure for the target achromatic band, thereby achieving achromatism that is polarization-insensitive in the target achromatic band.

Description

Technical Field

[0001] This application relates to microstructured optical devices, and particularly to a metasurface lens and a design method for a metasurface lens. Background Art

[0002] A metasurface lens is an optical lens designed using metasurface optical technology. Unlike traditional optical lenses with macroscopically visible curved surfaces, a metasurface lens uses an array of sub-wavelength unit structures (hereinafter simply referred to as "unit structures") arranged on the lens substrate to meet the curvature requirements for light refraction. Therefore, by configuring the unit structures, the refractive performance of the metasurface lens can be flexibly adjusted.

[0003] However, the chromatic aberration problem existing in traditional lenses also exists in metasurface lenses, that is, the energy focusing positions of light rays with different wavelengths after being refracted by the metasurface lens are dispersed in the optical axis direction, thereby presenting axial dispersion of light rays with different wavelengths after refraction. Moreover, the axial dispersion will result in different-sized diffused light spots on the same image plane. Although traditional optical lenses can achieve achromatism by fitting the curved surfaces of two lenses, this method is not applicable to metasurface lenses.

[0004] It can be seen that how to achieve achromatism of metasurface lenses has become a technical problem to be solved in the prior art, and this technical problem limits the application and popularization of metasurface lenses.

[0005] Among them, metasurface lenses can be divided into two categories: polarization-sensitive (or polarization-independent) and polarization-insensitive (or polarization-dependent). This application focuses on how to achieve achromatism of polarization-insensitive metasurface lenses. Summary of the Invention

[0006] In an embodiment of this application, a metasurface lens and a design method for a metasurface lens are provided, which can support the metasurface lens to achieve polarization-insensitive achromatism.

[0007] In one embodiment, a metasurface lens may include:

[0008] A lens substrate, and

[0009] An array of unit structures distributed on the lens substrate, where:

[0010] Each unit structure in the array of unit structures has a four-quadrant symmetry structure feature;

[0011] The four-quadrant symmetry structure features of the unit structures in the array of unit structures are not all the same, and the fact that the four-quadrant symmetry structure features are not all the same includes that the cross-sectional shape features of the four-quadrant symmetry structure features of the unit structures are not all the same in a cross-section parallel to the lens substrate;

[0012] The characteristic dimensions of the unit structures with the same quadrant symmetry structure characteristics in the unit structure array are not all the same.

[0013] In some examples, optionally, the unit structure array includes a first subset of unit structures, a second subset of unit structures, and a third subset of unit structures, where: the quadrant symmetry structure characteristics of each unit structure in the first subset of unit structures are all first-class quadrant symmetry structure characteristics, the characteristic dimensions of each unit structure in the first subset of unit structures are not all the same, and the first-class quadrant symmetry structure characteristics include: a fishing net node shape characteristic in which the cross-sectional shape in a cross-section parallel to the lens substrate is a circular and cross-shaped overlap; the quadrant symmetry structure characteristics of each unit structure in the second subset of unit structures are all second-class quadrant symmetry structure characteristics, the characteristic dimensions of each unit structure in the second subset of unit structures are not all the same, and the second-class quadrant symmetry structure characteristics include: an annular characteristic in which the cross-sectional shape in a cross-section parallel to the lens substrate is an annular shape; the quadrant symmetry structure characteristics of each unit structure in the third subset of unit structures are all third-class quadrant symmetry structure characteristics, the characteristic dimensions of each unit structure in the third subset of unit structures are not all the same, and the third-class quadrant symmetry structure characteristics include: a four-lobe shape characteristic in which the cross-sectional shape in a cross-section parallel to the lens substrate is four identical rectangles distributed at equal angles.

[0014] In some examples, optionally, the different characteristic dimensions of each unit structure in the first subset of unit structures include at least one of the radial dimension of the circle, the line length dimension of the cross, and the line width dimension of the cross; the different characteristic dimensions of each unit structure in the second subset of unit structures include at least one of the outer diameter dimension and the inner diameter dimension of the annulus; the different characteristic dimensions of each unit structure in the third subset of unit structures include at least one of the length and width dimensions of the rectangle and the distance dimension of the rectangle from the cross-section center.

[0015] In some examples, optionally, the reference phase and the compensation phase of each unit structure in the unit structure array are associated with the quadrant symmetry structure characteristics and the characteristic dimensions of the unit structure.

[0016] In some examples, optionally, each unit structure in the unit structure array matches the corresponding relationship between the reference phase and the compensation phase and the aperture position of the metasurface lens at the aperture position of the lens substrate, and, based on the corresponding relationship between the reference phase and the compensation phase and the aperture position of the metasurface lens: the compensation phase of each unit structure in the unit structure array has a changing trend that monotonically changes between the aperture center position and the aperture edge position of the metasurface lens, and the monotonic change amplitude between the compensation phase of the unit structure distributed at the aperture center position and the compensation phase of the unit structure distributed at the aperture edge position in the unit structure array is greater than or equal to a preset target phase difference distribution range, and the target phase difference distribution range matches the target parameters of the metasurface lens, and the target parameters include the aperture of the metasurface lens, the numerical aperture of the metasurface lens, and the bandwidth of the target achromatic band, and, the reference phase and the compensation phase of each unit structure in the unit structure array are interleaved within the target phase difference distribution range.

[0017] In some examples, optionally, each unit structure in the unit structure array occupies a quadrilateral region on the lens substrate, and the unit structures in the unit structure array are distributed in a grid pattern on the lens substrate, and, the period between the centers of every two adjacent unit structures in the unit structure array is equal.

[0018] In some examples, optionally, each unit structure in the unit structure array occupies a hexagonal region on the lens substrate, and the unit structures in the unit structure array are distributed in a honeycomb pattern on the lens substrate, and, the period between the centers of every two adjacent unit structures in the unit structure array is equal.

[0019] In some examples, optionally, the unit structures in the unit structure array are distributed in an annular belt pattern that wraps around the aperture center layer by layer on the lens substrate, and, the gap size between every two adjacent unit structures in the unit structure array is equal.

[0020] In some examples, optionally, the minimum dimension value of the feature size of the four-quadrant symmetry structure feature of each unit structure in the unit structure array is 0.7 μm.

[0021] In some examples, optionally, the minimum difference value between the feature sizes of the unit structures with the same four-quadrant symmetry structure feature in the unit structure array is 0.5 μm.

[0022] In some examples, optionally, the materials of the lens substrate and each unit structure in the unit structure array include silicon.

[0023] In some examples, optionally, the period between the centers of every two adjacent unit structures in the unit structure array is 3 μm - 6 μm.

[0024] In some examples, optionally, the height dimension of each unit structure in the unit structure array in a direction perpendicular to the lens substrate is greater than 5 μm.

[0025] Another embodiment of the present application provides a design method of a metasurface lens, which is characterized by including:

[0026] Providing a lens substrate;

[0027] Selecting unit structures that match each aperture position of the lens substrate from at least two pre-created unit families, where each unit family includes multiple unit structures with the same four-quadrant symmetry structure characteristics and different feature sizes, and the four-quadrant symmetry structure characteristics of the unit structures in different unit families are not all the same;

[0028] Deploying a unit structure array on the lens substrate by using the selected unit structures.

[0029] In some examples, optionally, the step of selecting unit structures that match each aperture position of the lens substrate from at least two pre-created unit families includes: selecting unit structures that match each aperture position of the lens substrate from at least two unit families according to the correspondence between the reference phase and the compensation phase and the aperture position of the metasurface lens;

[0030] The step of deploying a unit structure array on the lens substrate by using the selected unit structures includes: deploying unit structures that match each aperture position on the lens substrate, where in the deployed unit structure array: the compensation phases of the unit structures have a monotonic change trend between the aperture center position and the aperture edge position of the metasurface lens, and the monotonic change amplitude between the compensation phase of the unit structure at the aperture center position and the compensation phase of the unit structure at the aperture edge position is greater than or equal to a preset target phase difference distribution range, and the target phase difference distribution range matches the target parameters of the metasurface lens, and the target parameters include the aperture of the metasurface lens, the numerical aperture of the metasurface lens, and the bandwidth of the target achromatic band, and the compensation phase value ranges of at least two unit families stagger and cover the target phase difference distribution range.

[0031] In some examples, optionally, the correspondence between the reference phase and the compensation phase and the aperture position of the metasurface lens includes: the remainder of the reference phase of each unit structure divided by 2π is the same as the remainder of the target phase of the metasurface lens at the aperture position where the unit structure is located divided by 2π; the compensation phase of each unit structure is the same as the target phase difference of the metasurface lens at the aperture position where the unit structure is located.

[0032] In some examples, optionally, the correspondence between the reference phase and the compensation phase and the aperture position of the metasurface lens includes: the remainder result Mod(Φ, 2π) of the reference phase Φ of each unit structure divided by 2π, and the remainder result Mod(φ, 2π) of the target phase φ of the metasurface lens at the aperture position where the unit structure is located divided by 2π satisfy: Mod(Φ, 2π) = Mod(φ, 2π); and, the compensation phase ΔΦ corresponding to the achromatic band [λ1, λ2] of each unit structure λ1-λ2 , and the target phase difference Δφ corresponding to the achromatic band [λ1, λ2] of the metasurface lens at the aperture position where the unit structure is located λ1-λ2 satisfy: ΔΦ λ1-λ2 = Δφ λ1-λ2 , where λ1 is the first boundary wavelength of the target achromatic band [λ1, λ2], and λ2 is the second boundary wavelength of the target achromatic band [λ1, λ2].

[0033] In some examples, optionally: at the aperture position of any unit structure of the metasurface lens, for any wavelength in the target achromatic band the target phase satisfies:

[0034] , and represent the coordinate position in the rectangular coordinate system with the aperture center as the origin of the aperture position, represents the focal length of the metasurface lens;

[0035] wherein, the target phase of the metasurface lens at the aperture position of any unit structure is the first phase value when taking the reference wavelength in the target achromatic band, and the reference wavelength is the first boundary wavelength of the target achromatic band; the target phase difference of the metasurface lens at the aperture position of any unit structure is the difference between the second phase value when taking the second boundary wavelength in the target achromatic band and the first phase value.

[0036] In some examples, optionally, before providing the lens substrate, it further includes: creating at least two unit families according to a pre-determined target phase difference distribution range, and the at least two created unit families include a first unit family, a second unit family, and a third unit family, where: the four-quadrant symmetric structural feature of the first unit family is configured to make: the compensation phase value range of the first unit family includes multiple discrete range segments spanning the target phase difference distribution range; the four-quadrant symmetric structural feature of the second unit family is configured to make: the compensation phase value range of the second unit family fills the gaps formed by the discrete range segments of the first unit family in the first discrete distribution interval; the four-quadrant symmetric structural feature of the third unit family is configured to make: the compensation phase value range of the third unit family fills the gaps formed by the discrete range segments of the first unit family in the second discrete distribution interval; where, the upper limit of the absolute value of the compensation phase in the second discrete distribution interval is less than the lower limit of the absolute value of the compensation phase in the first discrete distribution interval.

[0037] In some examples, optionally: the multiple discrete range segments of the first unit family include: a first range segment, a second range segment, a third range segment, a fourth range segment, and a fifth range segment that are discretely arranged in ascending order of the absolute value of the compensation phase; the compensation phase value range of the second unit family includes: a sixth range segment filling between the second range segment and the third range segment, a seventh range segment filling between the third range segment and the fourth range segment, and an eighth range segment filling between the fourth range segment and the fifth range segment; the compensation phase value range of the third unit family includes: a ninth range segment filling between the first range segment and the second range segment, and a tenth range segment filling between the second range segment and the third range segment, and the tenth range segment is closer to the second range segment than the sixth range segment.

[0038] In some examples, optionally: the target achromatic band is 9μm to 14μm.

[0039] In some examples, optionally, before providing the lens substrate, it further includes: performing finite element analysis on each unit structure in the at least two created unit families; determining the height dimension of each unit structure in the at least two unit families in the direction perpendicular to the lens substrate, and the period between each unit structure and adjacent unit structures after being selected, according to the analysis value of the finite element analysis and the target transmittance of the pre-set unit structure.

[0040] Based on the above embodiments, each unit structure in the unit structure array of the metasurface lens has a four-quadrant symmetric structure feature, so that the metasurface lens is configured as a polarization-insensitive lens. Moreover, since the four-quadrant symmetric structure features of the unit structures in the unit structure array are not all the same, and the characteristic sizes of the unit structures with the same four-quadrant symmetric structure feature in the unit structure array are not all the same, it helps to improve the coverage ability of the reference phase and the compensation phase of each unit structure in the unit structure array for the target achromatic band, so that achromatism insensitive to polarization can be achieved in the target achromatic band. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The following drawings only illustrate and explain the present application and do not limit the scope of the present application:

[0042] Figure 1 is a schematic diagram of an exemplary structure of the metasurface lens in an embodiment of the present application;

[0043] Figure 2 is a schematic diagram of a curve example of the requirements for the reference phase of the metasurface lens in an embodiment of the present application at different aperture positions;

[0044] Figure 3 is a schematic diagram of a curve example of the requirements for the compensation phase of the metasurface lens in an embodiment of the present application at different aperture positions;

[0045] Figure 4 is a refraction effect diagram of the metasurface lens in an embodiment of the present application for light rays of different wavelengths;

[0046] Figure 5 is a schematic diagram of an example of the first unit family provided for the metasurface lens in an embodiment of the present application;

[0047] Figure 6 is a schematic diagram of an example of the second unit family provided for the metasurface lens in an embodiment of the present application;

[0048] Figure 7 is a schematic diagram of an example of the third unit family provided for the metasurface lens in an embodiment of the present application;

[0049] Figure 8 is a schematic diagram of an example of the distribution of the reference phase and the compensation phase of the multi-unit family provided for the metasurface lens in an embodiment of the present application;

[0050] Figure 9 is a schematic diagram of an example of the matching relationship between the compensation phase and the requirements of the multi-unit family provided for the metasurface lens in an embodiment of the present application;

[0051] Figure 10 is a schematic diagram of the metasurface lens in an embodiment of the present application when the unit structures are distributed in a grid pattern;

[0052] Figure 11 Schematic diagram of the metasurface lens in the embodiment of the present application when the unit structure adopts a honeycomb distribution;

[0053] Figure 12 Schematic diagram of the metasurface lens in the embodiment of the present application when the unit structure adopts an annular belt distribution;

[0054] Figure 13 Schematic flow chart of the design method provided for a metasurface lens in the embodiment of the present application;

[0055] Figure 14 Schematic diagram of an example curve of the 2π remainder principle provided for matching the unit structure of the metasurface lens in the embodiment of the present application. Detailed implementation manners

[0056] To make the objectives, technical solutions and advantages of the present application clearer and more understandable, the following further describes the present application in detail with reference to the accompanying drawings and by way of examples.

[0057] Figure 1 Exemplary structural schematic diagram of the metasurface lens in the embodiment of the present application. Please refer to Figure 1 , in the embodiment of the present application, the metasurface lens may include a lens substrate 10 and an array of unit structures distributed on the lens substrate 10. The array of unit structures includes a plurality of unit structures 30. Among them, the materials of the lens substrate 10 and all the unit structures 30 distributed on the lens substrate 10 may include silicon.

[0058] In the embodiment of the present application, each unit structure 30 has a four-quadrant symmetry structural feature, so that the metasurface lens in the embodiment of the present application is configured as a polarization-insensitive lens; and each unit structure 30 also has a reference phase and a compensation phase associated with its four-quadrant symmetry structural feature and feature size. Among them, the reference phase of each unit structure 30 refers to: the phase when the light of the reference wavelength in the target achromatic band of the metasurface lens is refracted under the control of this unit structure 30; and the compensation phase of each unit structure 30 refers to: the phase when the light of the wavelengths other than the reference wavelength in the target achromatic band of the metasurface lens is refracted under the control of this unit structure 30, which is the delay compared with the phase when the light of the reference wavelength is refracted under the control of this unit structure 30. That is, the compensation phase can be regarded as: the phase when the light of the wavelengths other than the reference wavelength in the target achromatic band is refracted under the control of this unit structure 30, minus the phase when the light of the reference wavelength is refracted under the control of this unit structure 30. Therefore, the compensation phase can also be called the phase difference.

[0059] In the embodiments of the present application, the quadrant symmetry structure features and feature sizes of each unit structure 30 in the unit structure array are associated with the aperture position of the unit structure on the lens substrate. Since the reference phase and compensation phase of each unit structure 30 in the unit structure array are both associated with the quadrant symmetry structure features and feature sizes of the unit structure, therefore, based on the association between the quadrant symmetry structure features and feature sizes of each unit structure 30 in the unit structure array and the aperture position of the unit structure 30 on the lens substrate, each unit structure 30 in the unit structure array can be distributed on the lens substrate 10 according to the correspondence between the reference phase and compensation phase and the aperture position of the metasurface lens.

[0060] Among them, the correspondence between the reference phase and compensation phase and the aperture position of the metasurface lens is used to characterize the requirements for the reference phase and compensation phase at different aperture positions of the metasurface lens. The goal of this requirement is that parallel light of different wavelengths in the target achromatic band can be focused on the same energy focusing position on the optical axis direction of the metasurface lens after being refracted at each aperture position of the metasurface lens.

[0061] Figure 2 It is a schematic diagram of an example curve of the requirements for the reference phase of the metasurface lens in the embodiments of the present application at different aperture positions. Figure 3 It is a schematic diagram of an example curve of the requirements for the compensation phase of the metasurface lens in the embodiments of the present application at different aperture positions. In Figure 2 and Figure 3 Taking the infrared band with a target achromatic band of 9 μm - 14 μm (bandwidth of 5 μm) as an example, and the reference wavelength in the target achromatic band is 9 μm.

[0062] Please first refer to Figure 2 , in which the abscissa value of the reference phase requirement curve shown represents the aperture position, the ordinate value represents the target phase φ (i.e., the requirement for the reference phase Φ), and the unit of the target phase φ, rad (radian), satisfies the value relationship that 3.14 rad is equal to π. Although Figure 2 only shows the reference phase requirement curves for the two boundary wavelengths of 9 μm and 14 μm, it can be understood that the reference phase requirement curves for the remaining wavelengths greater than 9 μm and less than 14 μm in the target achromatic band are distributed between the two reference phase requirement curves shown in Figure 2 .

[0063] Moreover, it can be seen from Figure 2 that in the reference phase requirement curve for each wavelength in the target achromatic band, the target phase φ representing the requirement for the reference phase Φ monotonically changes from the aperture center position (i.e., the position where the aperture position P is 0) to the aperture edge position.

[0064] In the embodiments of the present application, an optical lens design software such as zemax can be used to determine the reference phase demand curve. Moreover, when using the optical lens design software to determine the reference phase demand curve, at least one parameter among the aperture of the metasurface lens, the field of view angle, the field of view angle, and the F-number (i.e., the reciprocal of the relative aperture of the lens applying the metasurface lens) can be used.

[0065] In the embodiments of the present application, the reference phase demand curve may not be determined by using the optical lens design software, but may be determined according to the following expression (1), that is, for any wavelength in the target achromatic band corresponding to the aperture position where any unit structure of the metasurface lens is located the phase satisfies the following expression (1):

[0066] Expression (1)

[0067] where and represent the coordinate positions in the rectangular coordinate system with the aperture center as the origin, represents the focal length of the metasurface lens.

[0068] That is, for any aperture position of the metasurface lens (for example, the aperture position where any unit structure 30 is located), the target phase φ can be the first phase value when taking the reference wavelength in the target achromatic band, and this reference wavelength can be the first boundary wavelength of the target achromatic band (for example, any one of 9 μm and 14 μm).

[0069] Please refer to Figure 3 , where the abscissa value of the shown compensation phase demand curve represents the aperture position, and the ordinate value represents the target phase difference Δφ (i.e., the demand for the compensation phase ΔΦ). Where Figure 3 the shown target phase difference Δφ in is based on Figure 2 the shown reference phase demand curve in, that is, for each aperture position, the target phase difference Δφ can be: the difference between the values of the target phase φ corresponding to the first boundary wavelength (for example, any one of 9 μm and 14 μm) and the second boundary wavelength (for example, the other one of 9 μm and 14 μm) in the target achromatic band at this aperture position. For example, for any aperture position (the aperture position where any unit structure 30 is located) of the metasurface lens, the target phase difference Δφ can be the difference between the second phase value when taking the second boundary wavelength (for example, the other one of 9 μm and 14 μm) in the target achromatic band and the aforementioned first phase value.

[0070] In the embodiments of the present application, the unit structures 30 distributed on the lens substrate 10 all conform to the correspondence between the reference phase and the compensation phase characterized by the demand curve as shown in Figure 2 and Figure 3 and the aperture position of the metasurface lens, that is, the reference phase and the compensation phase of each unit structure 30 match the requirements for the reference phase and the compensation phase at the aperture position where the metasurface lens is located in the unit structure 30. Therefore, parallel light of different wavelengths in the target achromatic band can be refracted by each unit structure 30 and converge at the same energy focusing position on the optical axis direction of the metasurface lens.

[0071] Figure 4 FIG. Figure 4 shows the refraction effect diagram of the metasurface lens in the embodiments of the present application for light of different wavelengths. In Figure 4 , still taking the infrared band with a target achromatic band of 9 μm - 14 μm as an example, and Figure 4 shows the refraction effects of the metasurface lens in the embodiments of the present application on light of wavelengths 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, and 14 μm in the target achromatic band respectively. It can be seen from Figure 4 that the energy focusing points of the light of these five wavelengths after refraction are at the same position in the longitudinal direction representing the optical axis direction in Figure 4 , that is, the energy focusing positions of the light of these five wavelengths after refraction are aligned along the dotted line in

[0072] That is to say, based on the embodiments of the present application, the unit structure 30 of the metasurface lens can have a reference phase and a compensation phase associated with the four-quadrant symmetric structure characteristics and characteristic dimensions, and the unit structure 30 of the metasurface lens can be distributed on the lens substrate according to the correspondence between the reference phase and the compensation phase and the aperture position of the metasurface lens, that is, the four-quadrant symmetric structure characteristics and characteristic dimensions of each unit structure in the unit structure array are associated with the aperture position of the unit structure on the lens substrate, so as to cause parallel light of different wavelengths in the target achromatic band to be refracted by each unit structure and converge at the same energy focusing position on the optical axis direction of the metasurface lens, thereby achieving polarization-insensitive achromatism.

[0073] Still referring to Figure 3, the target phase difference Δφ representing the requirement for the compensation phase ΔΦ monotonically changes from the center position of the aperture (i.e., the position where the aperture position P is 0) to the edge position of the aperture. Therefore, in the embodiments of the present application, the compensation phases of all the unit structures 30 have a changing trend that monotonically changes between the center position and the edge position of the aperture of the metasurface lens. For example, among all the unit structures 30, the absolute value of the compensation phase of the unit structure located at the center position of the aperture of the metasurface lens is Φ1 (such as 0 or a value approaching 0), and the absolute value of the compensation phase of the unit structure located at the edge position of the aperture of the metasurface lens is Φ2 greater than Φ1.

[0074] Moreover, from Figure 3 the compensation phase demand curve shown in it can also be deduced that the magnitude of the monotonic change amplitude between the compensation phase and the compensation phase of the unit structure at the edge position of the aperture is related to the aperture size of the metasurface lens. Moreover, Figure 3 the curvature of the compensation phase demand curve shown in it is related to the NA (Numerical Aperture) of the metasurface lens and the bandwidth of the target achromatic band, that is, the larger the NA of the metasurface lens and the bandwidth of the target achromatic band, the greater the curvature of the compensation phase demand curve, and the smaller the NA of the metasurface lens and the bandwidth of the target achromatic band, the smaller the curvature of the compensation phase demand curve. In addition, NA is also related to the period P of the distribution of each unit structure 30 on the lens substrate 10, where the period P refers to the distance between the centers of every two unit structures 30 distributed on the lens substrate 10, and the period P is less than min{λ / 2NA, λ}, that is, the period P is less than the minimum value of λ / 2NA and λ, where λ represents the reference wavelength in the target achromatic band.

[0075] As described above, the reference phase and the compensation phase of each unit structure 30 are both associated with the four-quadrant symmetric structure feature and the feature size thereof. That is, the size variation range of the feature size of each type of four-quadrant symmetric structure feature can provide a selectable value range for the reference phase and the compensation phase of all unit structures 30 having this four-quadrant symmetric structure feature. Therefore, the reference phase and the compensation phase of each unit structure 30 are both within the selectable value range corresponding to the size variation range of the feature size of the four-quadrant symmetric structure feature of this unit structure 30. Moreover, the values of the reference phase and the compensation phase of each unit structure 30 within the corresponding selectable value range are associated with the feature size of this unit structure 30. Thus, the selectable value range corresponding to the size variation range of the feature size of each type of four-quadrant symmetric structure feature can characterize the adjustment ability for making the reference phase and the compensation phase match the reference phase requirement and the compensation phase requirement. Therefore, if all unit structures 30 have the same four-quadrant symmetric structure feature, then the magnitude of the monotonic change range between the compensation phase and the compensation phase of the unit structure at the aperture edge position is equal to the magnitude of the maximum phase difference adjustment range ΔΦ_max provided for the compensation phase by adjusting the feature size of this four-quadrant symmetric structure feature. This maximum phase difference adjustment range ΔΦ_max can be understood as the compensation phase value range supported by the feature size value range of a single type of four-quadrant symmetric structure feature. Correspondingly, the vertical coordinate change range of the reference phase requirement curve of the reference wavelength corresponding to this maximum phase difference adjustment range ΔΦ_max can be considered as the reference phase value range supported by the feature size value range of a single type of four-quadrant symmetric structure feature. Figure 2 In the vertical coordinate change range of the reference phase requirement curve of the reference wavelength corresponding thereto, it can be considered as the reference phase value range supported by the feature size value range of a single type of four-quadrant symmetric structure feature.

[0076] However, the magnitude of the maximum phase difference adjustment range ΔΦ_max provided by adjusting the feature size of the four-quadrant symmetric structure feature is limited. That is, the compensation phase value range supported by the feature size value range of a single type of four-quadrant symmetric structure feature has limitations. In this case, if it is necessary to increase the aperture of the metasurface lens, then at least one parameter value of the NA of the metasurface lens and the bandwidth of the target achromatic band needs to be reduced. That is, limited by the limitations of the compensation phase value range (i.e., the maximum phase difference adjustment range ΔΦ_max) supported by the feature size value range of a single type of four-quadrant symmetric structure feature, the parameter value ranges of the three parameters of the aperture of the metasurface lens, the NA of the metasurface lens, and the bandwidth of the target achromatic band cannot be expanded simultaneously.

[0077] In order to simultaneously achieve polarization-insensitive achromatism and take into account the expansion requirements of the parameter value ranges of the aperture, numerical aperture, and wavelength band width of the metasurface lens applicable to polarization-insensitive achromatism, in the embodiments of the present application, the unit structures 30 distributed on the lens substrate 10 adopt a configuration of mixing multiple quadrant-symmetric structural features, so as to avoid the limitations of the parameter value ranges of the aperture, NA, and the bandwidth of the target achromatic wavelength band of the metasurface lens being restricted by the compensation phase value range supported by the feature size value range of a single quadrant-symmetric structural feature. Among them, the unit structures with each quadrant-symmetric structural feature can be considered to belong to a unit family. Each unit family includes multiple unit structures with the same quadrant-symmetric structural feature and different feature sizes. The quadrant-symmetric structural features of the unit structures in different unit families are not all the same. Moreover, in the embodiments of the present application, the unit structures 30 distributed on the lens substrate 10 can include unit structures belonging to at least two unit families, that is:

[0078] The quadrant-symmetric structural features of the unit structures 30 in the unit structure array are not all the same. Among them, the fact that the quadrant-symmetric structural features of the unit structures in the unit structure array are not all the same can include that the cross-sectional shape features of the quadrant-symmetric structural features of the unit structures in the unit structure array in the cross-section parallel to the lens substrate are not all the same, and

[0079] the feature sizes of the unit structures in the unit structure array with the same quadrant-symmetric structural feature (such as the quadrant-symmetric structural feature with the same cross-sectional shape feature) are not all the same.

[0080] Since the quadrant-symmetric structural features of the unit structures in the unit structure array are not all the same, and the feature sizes of the unit structures in the unit structure array with the same quadrant-symmetric structural feature are not all the same, it is helpful to improve the coverage ability of the reference phase and compensation phase of the unit structures in the unit structure array for the target achromatic wavelength band, so that polarization-insensitive achromatism can be achieved in the target achromatic wavelength band.

[0081] Moreover, in accordance with the same principle as described above, in the embodiments of the present application, each unit structure 30 has a reference phase and a compensation phase associated with the feature size of the quadrant-symmetric structural feature of the unit family to which it belongs. The unit structures 30 belonging to at least two unit families are distributed on the lens substrate 10 according to the corresponding relationship between the reference phase and compensation phase and the aperture position of the metasurface lens. Based on this distribution method, parallel light of different wavelengths in the target achromatic wavelength band can be focused on the same energy focusing position on the optical axis direction of the metasurface lens after being refracted by each unit structure.

[0082] As described above, in the embodiments of the present application, the reference phase and the compensation phase of each unit structure 30 in the unit structure array are associated with the quadrant symmetry structure characteristics and feature sizes of the unit structure 30. Each unit structure 30 in the unit structure array matches the corresponding relationship between the reference phase and the compensation phase and the aperture position of the metasurface lens at the aperture position of the lens substrate 10. And, based on the corresponding relationship between the reference phase and the compensation phase and the aperture position of the metasurface lens:

[0083] The compensation phase of each unit structure 30 in the unit structure array has a monotonic change trend between the aperture center position and the aperture edge position of the metasurface lens;

[0084] The monotonic change amplitude between the compensation phase of the unit structure distributed at the aperture center position and the compensation phase of the unit structure distributed at the aperture edge position in the unit structure array can be greater than or equal to the preset target phase difference distribution range;

[0085] This target phase difference distribution range is associated with the target parameters of the metasurface lens. The target parameters of the metasurface lens include the aperture of the metasurface lens, the NA of the metasurface lens, and the bandwidth of the target achromatic band; and,

[0086] Since the value ranges of the compensation phases of at least two unit families are staggered, therefore, the reference phases and compensation phases of the unit structures 30 with different quadrant symmetry structure characteristics and feature sizes in the unit structure array can be staggered within the target phase difference distribution range; and, since the value ranges of the compensation phases of at least two unit families staggeredly cover the target phase difference distribution range, thus, the staggered distribution of the reference phases and compensation phases of each unit structure 30 in the unit structure array within the target phase difference distribution range can allow the target phase difference distribution range associated with the aperture of the metasurface lens, the NA of the metasurface lens, and the bandwidth of the target achromatic band to extend beyond the value range of the compensation phase of any unit family, thereby avoiding the limitation that the parameter values of the aperture and NA of the metasurface lens and the bandwidth of the target achromatic band are restricted by the value range of the compensation phase of a single unit family (i.e., the value range of the compensation phase supported by the value range of the feature sizes of a single type of quadrant symmetry structure characteristics), and further supporting the expansion of the parameter value ranges of the aperture and NA of the applicable metasurface lens that is insensitive to polarization and the bandwidth of the target achromatic band.

[0087] Please look back Figure 1, in the embodiments of the present application, taking at least two unit families including a first unit family 31, a second unit family 32, and a third unit family 33 as an example, and the cross-sectional shape characteristics of the four-quadrant symmetric structure features of each unit structure in the first unit family 31, the second unit family 32, and the third unit family 33 are different from each other in the cross-section parallel to the lens substrate 10. Accordingly, in the embodiments of the present application, the unit structures distributed on the lens substrate 10 may include at least one unit structure belonging to the first unit family 31 and at least one unit structure belonging to the second unit family 32, or include at least one unit structure belonging to the second unit family 32 and at least one unit structure belonging to the third unit family 33, or include at least one unit structure belonging to the first unit family 31 and at least one unit structure belonging to the third unit family 33, or include at least one unit structure belonging to the first unit family 31, at least one unit structure belonging to the second unit family 32, and at least one unit structure belonging to the third unit family 33.

[0088] That is, the unit structure array includes at least two of a first unit structure subset, a second unit structure subset, and a third unit structure subset. The unit structures in the first unit structure subset may be the unit structures belonging to the first unit family 31, the unit structures in the second unit structure subset may be the unit structures belonging to the second unit family 32, and the unit structures in the third unit structure subset may be the unit structures belonging to the third unit family 33.

[0089] Figure 5 This is a schematic diagram of an example of the first unit family provided by the embodiments of the present application for the metasurface lens. Please refer back while Figure 1 seeing also Figure 5 , in the embodiments of the present application, the first type of four-quadrant symmetric structure features of the first unit family 31 may include: the cross-sectional shape in the cross-section parallel to the lens substrate is a fishing net node shape overlapping a circle and a cross. Accordingly, the four-quadrant symmetric structure features of each unit structure in the first unit structure subset of the unit structure array are all the first type of four-quadrant symmetric structure features, and the characteristic dimensions of each unit structure in the first unit structure subset are not all the same.

[0090] Such as Figure 5The reference phase value range and compensation phase value range of the first unit family 31 shown, as well as the reference phase and compensation phase of the unit structure it belongs to, are all associated with the characteristic dimensions of the first type of four-quadrant symmetric structure feature (i.e., the fishing net node shape feature) of the first unit family 31. Moreover, the characteristic dimensions of the four-quadrant symmetric structure feature (i.e., the fishing net node shape feature) of the first unit family 31 include the radial dimension R1 of the circle, the line length dimension L1 of the cross, and the line width dimension W1 of the cross. Correspondingly, the different characteristic dimensions of each unit structure in the first unit structure subset of the unit structure array include at least one of the radial dimension R1 of the circle, the line length dimension L1 of the cross, and the line width dimension W1 of the cross.

[0091] That is, for the first unit family 31, by configuring at least one of the characteristic dimensions of the radial dimension R1 of the circle, the line length dimension L1 of the cross, and the line width dimension W1 of the cross, the first unit family 31 can include multiple unit structures with different reference phases and compensation phases. Moreover, the reference phase value range and compensation phase value range of the first unit family 31 are determined by the value ranges of the characteristic dimensions (i.e., the radial dimension R1, the line length dimension L1 of the cross, and the line width dimension W1 of the cross) of the first type of four-quadrant symmetric structure feature (i.e., the fishing net node shape feature).

[0092] In addition, Figure 5 In addition to showing the conventional form in which the circle and cross of the first unit family 31 are both prominently presented, it also shows a cross-shaped deformation form in which the circle is hidden due to R1 being less than W1, a circular deformation form in which the cross is hidden due to both L1 and W1 being less than R1, and there is also a special rectangular form when L1 and W1 are equal in the cross-shaped deformation form in which the circle is hidden due to R1 being less than W1. Thus, it can be understood that the four-quadrant symmetric structure feature of the first unit family 31 being the fishing net node shape feature only means that the adjustable characteristic dimensions of the first unit family 31 are the associated dimensions of the fishing net node shape feature, and does not mean that the cross-sectional shapes of all unit structures belonging to the first unit family 31 must simultaneously and prominently present overlapping circles and crosses.

[0093] Figure 6 This is a schematic diagram of an example of the second unit family provided by the embodiment of the present application for the metasurface lens. Please look back Figure 1 while referring to Figure 6 In the embodiment of the present application, the second type of four-quadrant symmetric structure feature of the second unit family 32 can include: an annular feature with an annular cross-sectional shape in a cross-section parallel to the lens substrate. Correspondingly, the four-quadrant symmetric structure features of each unit structure in the second unit structure subset of the unit structure array are all the second type of four-quadrant symmetric structure features, and the characteristic dimensions of each unit structure in the second unit structure subset are not all the same.

[0094] As Figure 6 shown, the reference phase value range and compensation phase value range of the second unit family 32, as well as the reference phase and compensation phase of the unit structures belonging to the second unit family 32, are all associated with the characteristic dimensions of the second type of four-quadrant symmetric structure feature (i.e., the circular ring feature) of the second unit family 32. Moreover, the characteristic dimensions of the four-quadrant symmetric structure feature (i.e., the circular ring feature) of the second unit family 32 may include the outer diameter dimension R2 and inner diameter dimension R3 of the circular ring. Correspondingly, the different characteristic dimensions of the unit structures in the first unit structure subset of the unit structure array include at least one of the outer diameter dimension R2 and inner diameter dimension R3 of the circular ring.

[0095] That is, for the second unit family 32, by configuring at least one of the characteristic dimensions of the outer diameter dimension R2 and inner diameter dimension R3 of the circular ring, the second unit family 32 can include multiple unit structures with different reference phases and compensation phases. Moreover, the reference phase value range and compensation phase value range of the second unit family 32 are determined by the value ranges of the characteristic dimensions (i.e., the outer diameter dimension R2 and inner diameter dimension R3 of the circular ring) of the second type of four-quadrant symmetric structure feature (i.e., the circular ring feature).

[0096] Figure 7 This is a schematic diagram of an example of the third unit family provided by the embodiment of the present application for the metasurface lens. Please refer back Figure 1 while referring to Figure 7 . In the embodiment of the present application, the third type of four-quadrant symmetric structure feature of the third unit family 33 may include: a four-lobe feature with a cross-sectional shape of four identical rectangles equally angularly distributed in a cross-section parallel to the lens substrate. Correspondingly, the four-quadrant symmetric structure features of the unit structures in the third unit structure subset of the unit structure array are all the third type of four-quadrant symmetric structure features, and the characteristic dimensions of the unit structures in the third unit structure subset are not all the same.

[0097] As Figure 7 shown, the reference phase value range and compensation phase value range of the third unit family 33, as well as the reference phase and compensation phase of the unit structures belonging to the third unit family 33, are all associated with the characteristic dimensions of the four-quadrant symmetric structure feature (i.e., the four-lobe feature) of the third unit family 33. Moreover, the characteristic dimensions of the third type of four-quadrant symmetric structure feature (i.e., the four-lobe feature) of the third unit family 33 may include the length and width dimensions L3 and W3 of the rectangle, as well as the distance dimension D3 of the rectangle relative to the cross-section center. Correspondingly, the different characteristic dimensions of the unit structures in the third unit structure subset of the unit structure array include at least one of the length and width dimensions L3 and W3 of the rectangle, and the distance dimension D3 of the rectangle relative to the cross-section center.

[0098] That is, for the third unit family 33, by configuring at least one of the characteristic dimensions of the length L3 and width W3 of the rectangle and the distance dimension D3 of the rectangle relative to the center of the cross-section, the third unit family 33 can include multiple unit structures with different reference phases and compensation phases. Moreover, the value ranges of the reference phase and compensation phase of the third unit family 33 are determined by the value ranges of the characteristic dimensions (i.e., the length L3 and width W3 of the rectangle and the distance dimension D3 of the rectangle relative to the center of the cross-section) of the third type of four-quadrant symmetric structure feature (i.e., the four-lobe feature).

[0099] As can be seen above, the four-quadrant symmetric structure features of the first unit family 31, the second unit family 32, and the third unit family 33 are different from each other. For example, the cross-sectional shape features of the four-quadrant symmetric structure features of the first unit family 31, the second unit family 32, and the third unit family 33 in the cross-section parallel to the lens substrate 10 are different. That is, the cross-sectional shape of the first type of four-quadrant symmetric structure feature of the first unit family 31 in the cross-section parallel to the lens substrate is in the shape of a fishing net node where a circle and a cross overlap, the cross-sectional shape of the second type of four-quadrant symmetric structure feature in the cross-section parallel to the lens substrate is in the shape of an annular ring, and the cross-sectional shape of the third type of four-quadrant symmetric structure feature of the third unit family 33 in the cross-section parallel to the lens substrate is in the shape of a four-lobe formed by four identical rectangles with equal angular distribution. Therefore, based on the combined use of the four-quadrant symmetric structure features of the first unit family 31, the second unit family 32, and the third unit family 33, the design freedom of the unit structure can be enriched. In actual design, for the characteristic dimensions of the four-quadrant symmetric structure features of each unit family among the first unit family 31, the second unit family 32, and the third unit family 33, the minimum dimension value can be set to 0.7 μm (i.e., the minimum dimension value of the characteristic dimensions of the four-quadrant symmetric structure features of each unit structure in the unit structure array is 0.7 μm), and / or the adjustment step can be 0.5 μm (i.e., the minimum difference value of any characteristic dimension of different unit structures in the same unit family is 0.5 μm, and the minimum difference value between the characteristic dimensions of the unit structures with the same four-quadrant symmetric structure feature in the unit structure array is 0.5 μm).

[0100] Moreover, the value ranges of the reference phases provided by the first unit family 31, the second unit family 32, and the third unit family 33 through different characteristic dimensions of different four-quadrant symmetric structure features are all greater than 2π, and the value ranges of the compensation phases provided by the first unit family 31, the second unit family 32, and the third unit family 33 through different characteristic dimensions of different four-quadrant symmetric structure features intersect with each other.

[0101] Figure 8 This is a schematic diagram of the distribution examples of the reference phase and compensation phase of the multi-unit family provided by the embodiments of the present application for the metasurface lens. In Figure 8Among them, a cluster-shaped point cloud is used to represent the compensation phase value range of each unit family. Moreover, the coordinate values of all coordinate points in the cluster-shaped point cloud of each unit family represent the reference phase and compensation phase corresponding to all available unit structures that can be arranged on the lens substrate 10 in this unit family.

[0102] Please refer to Figure 8 , in the embodiments of the present application:

[0103] Based on at least one characteristic dimension among the radial dimension R1 of the circle, the line length dimension L1 of the cross, and the line width dimension W1 of the cross, the first type of four-quadrant symmetric structure feature (i.e., the fishing net node shape feature) of the first unit family 31 can be configured such that: the compensation phase value range of the first unit family 31 includes multiple discrete range segments S1 - S5. For example, the multiple discrete range segments S1 - S5 of the first unit family 31 can specifically include, in the order of the absolute value of the compensation phase from small to large, the first range segment S1, the second range segment S2, the third range segment S3, the fourth range segment S4, and the fifth range segment S5. Correspondingly, the compensation phase of each unit structure in the first unit structure subset of the unit structure array is distributed in any one of the first range segment S1, the second range segment S2, the third range segment S3, the fourth range segment S4, and the fifth range segment S5;

[0104] Based on at least one characteristic dimension among the outer diameter dimension R2 and the inner diameter dimension R3 of the circular ring, the second type of four-quadrant symmetric structure feature (i.e., the circular ring feature) of the second unit family 32 can be configured such that: the compensation phase value range S6 - S8 of the second unit family 32 fills the gaps formed by the discrete range segments of the first unit family 31 in the first discrete distribution interval. For example, the compensation phase value range S6 - S8 of the second unit family 32 can specifically include the sixth range segment S6 filled between the second range segment S2 and the third range segment S3, the seventh range segment S7 filled between the third range segment S3 and the fourth range segment S4, and the eighth range segment S8 filled between the fourth range segment S4 and the fifth range segment S5. Correspondingly, the compensation phase of each unit structure in the second unit structure subset of the unit structure array is distributed in any one of the sixth range segment S6, the seventh range segment S7, and the eighth range segment S8;

[0105] Based on at least one characteristic dimension among the length and width dimensions L3 and W3 of the rectangle, and the distance dimension D3 of the rectangle relative to the center of the cross-section, the third type of quadrant-symmetric structural feature (i.e., the four-lobe feature) of the third unit family 33 can be configured such that: the compensation phase value range S9 - S10 of the third unit family 33 fills the gap formed by the discrete range segments of the first unit family 31 in the second discrete distribution interval. For example, the compensation phase value range S9 - S10 of the third unit family 33 can specifically include the ninth range segment S9 filled between the first range segment S1 and the second range segment S2, and the tenth range segment S10 filled between the second range segment S2 and the third range segment S3. Correspondingly, the compensation phase of each unit structure in the third unit structure subset of the unit structure array is distributed in any one of the ninth range segment S9 and the tenth range segment S10;

[0106] Among them, the upper limit of the absolute value of the compensation phase in the second discrete distribution interval is less than the lower limit of the absolute value of the compensation phase in the first discrete distribution interval. That is, the first discrete distribution interval can be considered as the high absolute value distribution interval of the compensation phase, and the second discrete distribution interval can be considered as the low absolute value distribution interval of the compensation phase. Correspondingly, the tenth range segment S10 of the third unit family 33 can be closer to the second range segment S2 of the first unit family 31 than the sixth range segment S6 of the second unit family 32.

[0107] As can be seen above, although the compensation phase value range provided by the characteristic dimensions of the quadrant-symmetric structural features (such as the fishing net node shape feature, the circular ring feature, or the four-lobe feature) of each unit family (such as any one of the first unit family 31, the second unit family 32, and the third unit family 33) is limited, however, since the unit structures 30 in the embodiments of the present application belong to at least two unit families (such as the first unit family 31, the second unit family 32, and the third unit family 33), and in the embodiments of the present application, the compensation phase value ranges of at least two unit families are interleaved with each other. Therefore, the target phase difference distribution range covered by the interleaved compensation phase value ranges of at least two unit families can exceed the compensation phase value range of a single unit family. For example, the compensation phase value range of any unit family can be 35 rad. Based on the interleaving of the compensation phase value ranges of at least two unit families, the target phase difference distribution range can exceed 35 rad and even reach 70 rad.

[0108] Figure 9 This is an example schematic diagram of the matching relationship between the compensation phases of multiple unit families provided by the embodiments of the present application for the metasurface lens. In Figure 9 Each asterisk " The abscissa value of "" is used to represent the target phase of a requirement, and the ordinate value is used to represent a target phase difference corresponding to the target phase represented by the abscissa within the target phase difference distribution range S_obj. Starting from Figure 9 As can be seen from Figure 9 , multiple discrete range segments S1 - S5 of the first unit family 31 are discretely distributed in a manner that spans the target phase difference distribution range S_obj. Moreover, through the compensation phase value ranges S6 - S8 of the second unit family 32 and the compensation phase value ranges S9 - S10 of the third unit family 33 to fill the gaps between the multiple discrete range segments S1 - S5, the target phase difference distribution range S_obj can be interleavingly covered by the compensation phase value ranges S1 - S10 of the first unit family 31, the second unit family 32, and the third unit family 33.

[0109] Thus, it is possible to avoid the parameter values of the aperture and NA of the metasurface lens, as well as the bandwidth of the target achromatic band, being limited by the limitations of the compensation phase value range, and further support the expansion of the parameter value ranges of the aperture and NA of the applicable metasurface lens that is insensitive to polarization, as well as the bandwidth of the target achromatic band.

[0110] Based on the above principle in the embodiments of the present application, when designing a metasurface lens, multiple available unit structures of each unit family (such as the first unit family 31, the second unit family 32, and the third unit family 33) can be created first, and the structural data of the created multiple available unit structures (including the family identifier of the unit family to which the available unit structure belongs, as well as the reference phase and compensation phase of the available unit structure) can be stored in the structure library until the compensation phases of the available unit structures of each unit family stored in the structure library can exhaust or approach exhausting all the values within the compensation phase value range of the unit family. Then, according to the requirements for the reference phase and compensation phase at each aperture position of the metasurface lens (such as Figure 9 the asterisk "" in Figure 9 ""s coordinate value), unit structures whose reference phase and compensation phase both match the requirements are selected from the available unit structures of at least two unit families as the unit structures 30 distributed on the lens substrate 10 at this aperture position. That is, each unit structure 30 of the metasurface lens as shown in Figure 1 is selected from the structure library and can be any available unit structure of any unit family stored in the structure library.

[0111] When creating available unit structures for each unit family, finite element software such as FDTD (Finite Difference Time Domain) or COMSOL can be used to analyze and determine the reference phase and compensation phase of each available unit structure with different characteristic dimensions. Compared with the macroscopic analysis method based on Neff (equivalent refractive index), the reference phase and compensation phase obtained by finite element analysis have a higher correlation with the structural characteristics and are thus more accurate. Moreover, when using finite element software to analyze and determine the reference phase and compensation phase of each available unit structure with different characteristic dimensions, the transmittance of each available unit structure can also be obtained simultaneously. The transmittance of each available unit structure is related to its height dimension in the direction perpendicular to the lens substrate and its period during deployment. Therefore, when creating available unit structures for each unit family, the height dimension and the period during deployment of each available unit structure can be set so that its transmittance meets the target transmittance. For example, the height dimension of each unit structure in each unit family can be greater than 5 μm (preferably 30 μm), and the period can be 3 μm - 6 μm (preferably 3.5 μm). Correspondingly, the height dimension of each unit structure in the unit structure array in the direction perpendicular to the lens substrate can be greater than 5 μm, and the period between the centers of every two adjacent unit structures in the unit structure array can be 3 μm - 6 μm.

[0112] That is, among the available unit structures of each unit family stored in the structure library, the height dimension H1 of the available unit structure of the first unit family 31 as shown in Figure 5 , the height dimension H2 of the available unit structure of the second unit family 32 as shown in Figure 6 , and the height dimension H3 of the available unit structure of the third unit family 33 as shown in Figure 7 can all be set to values that make the transmittance meet the target transmittance. Correspondingly, the structural data of each available unit structure stored in the structure library can also include the height dimension of the available unit structure. Since all the unit structures 30 distributed on the lens substrate 10 are selected from the available unit structures of each unit family stored in the structure library, the height dimension of each unit structure 30 distributed at each aperture position on the lens substrate 10 in the unit structure array in the direction perpendicular to the lens substrate, and the value of the period between the unit structure 30 and the adjacent unit structure 30 are all analysis values determined based on finite element analysis, so as to ensure that the transmittance of each unit structure 30 in the unit structure array is greater than or equal to the preset target transmittance.

[0113] Figure 10 This is a schematic diagram of the metasurface lens of the embodiment of the present application when the unit structures are distributed in a grid pattern. Figure 11Schematic diagram of the metasurface lens according to the embodiment of the present application when the unit structure is in a honeycomb distribution. Figure 12 Schematic diagram of the metasurface lens according to the embodiment of the present application when the unit structure is in an annular distribution. In Figures 10 to 12 this example, taking at least two unit families including the first unit family 31, the second unit family 32, and the third unit family 33 as an example:

[0114] Each unit structure 30 occupies a quadrilateral area on the lens substrate 10, so that all unit structures 30 are distributed in a grid pattern as shown in Figure 10 the figure, and the period P between the centers of every two adjacent unit structures 30 is equal; or,

[0115] Each unit structure 30 occupies a hexagonal area on the lens substrate 10, so that all unit structures 30 are distributed in a honeycomb pattern as shown in Figure 11 the figure, and the period P between the centers of every two adjacent unit structures 30 is equal; or,

[0116] All unit structures 30 are distributed in an annular pattern around the center of the aperture layer by layer as shown in Figure 12 the figure, and the period P when the unit structures 30 are distributed in an annular pattern may not be a fixed value.

[0117] In the embodiment of the present application, the metasurface lens may further include a metal thin film covering the unit structure 30. Among them, when the unit structure 30 is distributed in an annular pattern as shown in Figure 12 the figure, although the period P is unequal, the gap size between every two adjacent unit structures 30 can be equal to improve the support effect on the metal thin film and is beneficial to the coating of the metal thin film.

[0118] Figure 13 Schematic flow chart of the design method provided for a metasurface lens according to an embodiment of the present application. Please refer to Figure 13 , in the embodiment of the present application, the design method of the metasurface lens may specifically include:

[0119] S1310: Provide a lens substrate.

[0120] S1330: Select unit structures that match each aperture position of the lens substrate from at least two pre-created unit families. Each unit family includes multiple unit structures with the same four-quadrant symmetry structure characteristics but different feature sizes, and the four-quadrant symmetry structure characteristics of the unit structures in different unit families are not all the same. For example, as described above, the fact that the four-quadrant symmetry structure characteristics of the unit structures in the unit structure array are not all the same can include that the cross-sectional shape characteristics of the four-quadrant symmetry structure characteristics of the unit structures in the unit structure array in a cross-section parallel to the lens substrate are not all the same.

[0121] S1350: Deploy the unit structure array on the lens substrate using the selected unit structures. For example, S1350 can generate unit structure layout data that contains the correspondence between each aperture position of the lens substrate and the structure identifier of the unit structure selected for that aperture position. Moreover, the metasurface lens designed by deploying the unit structure array on the lens substrate using the selected unit structures can include the metasurface lens as shown in Figure 1 .

[0122] Based on the above process, each unit structure in the unit structure array of the designed metasurface lens has four-quadrant symmetry structure characteristics, so that the metasurface lens is configured as a polarization-insensitive lens. Also, because the four-quadrant symmetry structure characteristics of the unit structures in the unit structure array are not all the same, and the feature sizes of the unit structures with the same four-quadrant symmetry structure characteristics in the unit structure array are not all the same, it helps to improve the coverage ability of the reference phase and compensation phase of each unit structure in the unit structure array for the target achromatic band. On this basis, based on the association between the four-quadrant symmetry structure characteristics and feature sizes of each unit structure in the unit structure array and the aperture position of the unit structure on the lens substrate, parallel light of different wavelengths in the target achromatic band can be refracted by each unit structure and converge at the same energy focusing position on the optical axis direction of the metasurface lens, thereby achieving polarization-insensitive achromatism.

[0123] In S1330, the surface area of the lens substrate can be divided according to the preset unit size of the unit structure, and based on the regional position of each divided unit area, the aperture position for deploying the unit structure is determined. For example, the center position of each unit area can be determined as an aperture position for deploying the unit structure. When dividing the surface area of the lens substrate in S1330, it can be divided according to any one of the arrangement methods as shown in Figures 10 to 12 .

[0124] In S1330, it is also possible to determine the target phase and target phase difference corresponding to the aperture position where each unit structure for deployment is located. For example, the target phase and target phase difference determined in this step can be determined based on Figure 2 and Figure 3 the demand curves shown in, and can be presented as Figure 9 the asterisk " " shown in.

[0125] After determining the aperture position where the unit structure for deployment is located in S1330 and determining the target phase and target phase difference corresponding to the aperture position where each unit structure for deployment is located, it is also possible to select the unit structure to be deployed on the lens substrate at this aperture position from the available unit structures in at least two unit families based on the target phase and target phase difference corresponding to the aperture position where each unit structure for deployment is located, as well as the reference phase and compensation phase of the available unit structures in at least two unit families. For example, it can be determined by referring to the coordinate matching relationship between the asterisk " Figure 9 " in and the cluster point cloud. ".

[0126] Specifically, as described above, since the reference phase and compensation phase of each unit structure are associated with the quadrant symmetry structure characteristics and feature sizes of the unit structure, when selecting the unit structure that matches each aperture position of the lens substrate from at least two pre-created unit families, the unit structure that matches each aperture position of the lens substrate can be selected from at least two unit families based on the corresponding relationship between the reference phase and compensation phase and the aperture position of the metasurface lens.

[0127] In this case, when using the selected unit structure to deploy the unit structure array on the lens substrate, the unit structure that matches this aperture position can be deployed at each aperture position of the lens substrate, so that in the deployed unit structure array: the compensation phases of the unit structures have a monotonic change trend between the aperture center position and the aperture edge position of the metasurface lens, and the monotonic change amplitude between the compensation phase of the unit structure at the aperture center position and the compensation phase of the unit structure at the aperture edge position is greater than or equal to the preset target phase difference distribution range, and the target phase difference distribution range matches the target parameters of the metasurface lens, and the target parameters include the aperture of the metasurface lens, the numerical aperture of the metasurface lens, and the bandwidth of the target achromatic band, and the compensation phase value ranges of at least two unit families stagger and cover the target phase difference distribution range.

[0128] In the embodiments of the present application, the correspondence between the reference phase and the compensation phase based on which the unit structure is selected and the aperture position of the metasurface lens may include a matching relationship in which the compensation phase ΔΦ is equal to the target phase difference Δφ. This matching relationship means that the compensation phase ΔΦ of each unit structure 30 distributed on the lens substrate 10 is the same as the target phase difference Δφ of the metasurface lens at the aperture position where the unit structure is located. That is, the compensation phase ΔΦ of each unit structure 30 distributed on the lens substrate 10 corresponding to the achromatic band [λ1, λ2] λ1-λ2 , is the same as the target phase difference Δφ of the metasurface lens at the aperture position where the unit structure is located corresponding to the achromatic band [λ1, λ2] λ1-λ2 , and it can be expressed as the following expression (2):

[0129] ΔΦ λ1-λ2 =Δφ λ1-λ2 Expression (2)

[0130] In the above expression, λ1 refers to the first boundary wavelength of the target achromatic band (for example, 9 μm), and λ2 refers to the second boundary wavelength of the target achromatic band (for example, 14 μm).

[0131] In the embodiments of the present application, when selecting the unit structure that matches each aperture position of the lens substrate from the available unit structures of at least two pre-created unit families, the matching of the reference phase and the target phase is also considered. If the principle of complete equality is also adopted for the matching of the reference phase and the target phase, it may lead to a decrease in the selection hit rate of the unit structure. For example, if the reference phase of a certain aperture position is 3π, and the reference phases of all available unit structures with a compensation phase equal to the target phase difference of this aperture position in at least two unit families are not equal to 3π, then a matching unit structure cannot be selected for this aperture position from the available unit structures of at least two unit families.

[0132] To improve the selection hit rate of the available unit structures, the embodiments of the present application consider that the fluctuation period of light is 2π. The correspondence between the reference phase and the compensation phase based on which the unit structure is selected and the aperture position of the metasurface lens may also include a matching relationship between the reference phase Φ and the target phase φ realized by the principle of taking the remainder of 2π. The matching relationship between the reference phase Φ and the target phase φ at each aperture position can be expressed as the following expression (3):

[0133] Mod(Φ, 2π) = Mod(φ, 2π) Expression (3)

[0134] Among them, Mod() represents the remainder function. The operation result of the remainder function Mod() can be the absolute value of the remainder after dividing the reference phase Φ or the target phase φ by 2π, or the operation result of the remainder function Mod() can be the absolute value of the sum of the remainder after dividing the reference phase Φ or the target phase φ by 2π and a preset compensation parameter. Or, the operation result of the remainder function Mod() can also be the remainder result obtained by taking the reference phase Φ or the target phase φ as part of the dividend and 2π as part of the divisor. The specific operation rule of the remainder function Mod() in the embodiments of the present application is not particularly limited, as long as the matching between the reference phase Φ and the target phase φ is within the phase range of 0-2π.

[0135] Figure 14 This is a schematic diagram of a curve example of the 2π remainder principle provided by the embodiments of the present application for matching the unit structure of the metasurface lens. In Figure 14 it shows the deformed curve after the 2π remainder operation of the reference phase demand curve of the reference wavelength (i.e., 9μm) as shown in Figure 2 . And, by comparing Figure 2 and Figure 14 it can be seen that the 2π remainder processing of the reference phase demand curve produces an effect similar to folding the reference phase demand curve within the phase range of 0-2π, as shown in Figure 8 and Figure 9 . In the horizontal coordinate direction, the reference phase Φ of each available unit structure and the distribution of the target phase φ at each aperture position (i.e., the region position determined in step 1330 in Figure 13 ) are all compressed within the value range with an absolute value of 0-2π through the 2π remainder processing.

[0136] Still assuming that the reference phase at a certain aperture position is 3π, although the reference phases of all available unit structures with a compensation phase equal to the target phase difference at this aperture position are not equal to 3π, there are available unit structures with reference phases of 5π and 7π respectively. Therefore, based on the principle of 2π remainder, a matching available unit structure with the same remainder result of π can be selected from them at this aperture position. Thus, based on the 2π remainder principle for matching the reference phase Φ and the target phase φ, it can improve the selection hit rate of available unit structures and enrich the design freedom of microstructures.

[0137] That is, in the embodiments of the present application, all unit structures 30 distributed on the lens substrate 10 can satisfy the following principle:

[0138] The remainder result of the reference phase Φ of each unit structure 30 divided by 2π is the same as the remainder result of the target phase φ of the metasurface lens at the aperture position where this unit structure 30 is located divided by 2π;

[0139] The compensation phase of each unit structure 30 is the same as the target phase difference of the metasurface lens at the aperture position where the unit structure 30 is located.

[0140] The design method of the embodiment of the present application may further include, before S1310: creating at least two unit families according to a pre-determined target phase difference distribution range. For example, the at least two unit families created may include the first unit family 31, the second unit family 32, and the third unit family 33 respectively shown as Figure 5 , Figure 6 and Figure 7 .

[0141] In addition, in order to make the transmittance of each unit structure in the designed unit structure array greater than or equal to a preset target transmittance, the design method of the embodiment of the present application may further include, before S1310: performing finite element analysis on each unit structure in the at least two created unit families;

[0142] Determine the height dimension of each unit structure in the at least two unit families in the direction perpendicular to the lens substrate, and the period between each selected unit structure and adjacent unit structures according to the analysis value of the finite element analysis and the preset target transmittance of the unit structure.

[0143] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A metasurface lens, characterized in that, Comprising: a lens substrate, and an array of unit structures distributed on the lens substrate, wherein: each unit structure in the array of unit structures has a four-quadrant symmetry structure feature; wherein, the array of unit structures includes at least two of a first subset of unit structures, a second subset of unit structures, and a third subset of unit structures; the four-quadrant symmetry structure features of the unit structures in the array of unit structures are not all the same, and, the fact that the four-quadrant symmetry structure features are not all the same includes that the cross-sectional shape features of the four-quadrant symmetry structure features of the unit structures in the cross-section parallel to the lens substrate are not all the same; wherein, the first type of four-quadrant symmetry structure features of the unit structures in the first subset of unit structures include a fishnet node shape feature in which a circle intersects with a cross in the cross-section parallel to the lens substrate, the second type of four-quadrant symmetry structure features of the unit structures in the second subset of unit structures include an annular feature in which the cross-sectional shape in the cross-section parallel to the lens substrate is an annulus, and the third type of four-quadrant symmetry structure features of the unit structures in the third subset of unit structures include a four-petal shape feature in which the cross-sectional shape in the cross-section parallel to the lens substrate is four identical rectangles equally angularly distributed; the characteristic dimensions of the unit structures with the same four-quadrant symmetry structure feature in the array of unit structures are not all the same; wherein, the different characteristic dimensions of the unit structures in the first subset of unit structures include at least one of the radial dimension of the circle, the line length dimension of the cross, and the line width dimension of the cross, the different characteristic dimensions of the unit structures in the second subset of unit structures include at least one of the outer diameter dimension and the inner diameter dimension of the annulus, and the different characteristic dimensions of the unit structures in the third subset of unit structures include at least one of the length and width dimensions of the rectangle and the distance dimension of the rectangle from the cross-section center.

2. The metasurface lens according to claim 1, wherein each unit structure in the array of unit structures occupies a quadrilateral region on the lens substrate, the unit structures in the array of unit structures are distributed in a grid pattern on the lens substrate, and, the period between the centers of every two adjacent unit structures in the array of unit structures is equal.

3. The metasurface lens according to claim 1, wherein each unit structure in the array of unit structures occupies a hexagonal region on the lens substrate, the unit structures in the array of unit structures are distributed in a honeycomb pattern on the lens substrate, and, the period between the centers of every two adjacent unit structures in the array of unit structures is equal.

4. The metasurface lens according to claim 1, wherein the unit structures in the array of unit structures are distributed in an annular belt pattern around the aperture center layer by layer, and, the gap size between every two adjacent unit structures in the array of unit structures is equal.

5. The metasurface lens according to any one of claims 1 to 3, wherein the minimum value of the characteristic dimension of the four-quadrant symmetry structure feature of each unit structure in the array of unit structures is 0.7 μm, and / or, The minimum difference value between the characteristic dimensions of each unit structure having the same four - quadrant symmetry structure feature in the unit structure array is 0.5 μm, and / or, The materials of the lens substrate and each unit structure in the unit structure array include silicon, and / or, The period between the centers of every two adjacent unit structures in the unit structure array is 3 μm - 6 μm, and / or, The height dimension of each unit structure in the unit structure array in the direction perpendicular to the lens substrate is greater than 5 μm.

6. A design method of a metasurface lens, characterized in that This design method is used to design the metasurface lens as described in any one of claims 1 to 5, and this design method includes: Providing a lens substrate; According to the correspondence between the reference phase and the compensation phase and the aperture position of the metasurface lens, selecting unit structures that match each aperture position of the lens substrate from at least two pre - created unit families; wherein, the reference phase of each unit structure is the phase when the light of the reference wavelength is controlled to refract by the unit structure; the reference wavelength is the first boundary wavelength λ1 of the target achromatic band [λ1, λ2] of the metasurface lens; the compensation phase of each unit structure is: the delay of the phase when the light of the remaining wavelengths except the reference wavelength in the target achromatic band [λ1, λ2] of the metasurface lens is controlled to refract by the unit structure compared to the phase when the light of the reference wavelength is controlled to refract by the unit structure; each unit family includes multiple unit structures having the same four - quadrant symmetry structure feature and different characteristic dimensions, and the four - quadrant symmetry structure features of the unit structures in different unit families are not all the same; Using the selected unit structures to deploy a unit structure array including at least two of a first unit structure subset, a second unit structure subset, and a third unit structure subset on the lens substrate; wherein, the at least two unit families include a first unit family, a second unit family, and a third unit family, the unit structures in the first unit structure subset belong to the first unit family, the unit structures in the second unit structure subset belong to the second unit family, and the unit structures in the third unit structure subset belong to the third unit family; Wherein, the using the selected unit structures to deploy the unit structure array on the lens substrate includes: deploying the unit structures that match each aperture position at each aperture position of the lens substrate; Wherein, in the deployed unit structure array: the compensation phases of each unit structure have a monotonically changing trend between the aperture center position and the aperture edge position of the metasurface lens, and the monotonic change amplitude between the compensation phase of the unit structure at the aperture center position and the compensation phase of the unit structure at the aperture edge position is greater than or equal to a preset target phase difference distribution range, and the target phase difference distribution range matches the target parameters of the metasurface lens, and the target parameters include the aperture of the metasurface lens, the numerical aperture of the metasurface lens, and the bandwidth of the target achromatic band [λ1, λ2], and the compensation phase value ranges of at least two unit families stagger - cover the target phase difference distribution range; Among them, the target phase difference at the aperture position where any unit structure of the metasurface lens is located is: the difference between the phase value when the wavelength λ in the target achromatic band [λ1, λ2] corresponding to this aperture position of the metasurface lens takes the second boundary wavelength λ2 and the target phase, and the target phase is the phase value when the wavelength λ in the target achromatic band [λ1, λ2] corresponding to this aperture position of the metasurface lens takes the reference wavelength.

7. The design method according to claim 6, characterized in that The corresponding relationship between the reference phase and the compensation phase and the aperture position of the metasurface lens includes: The remainder result Mod(Φ, 2π) of the reference phase Φ of each unit structure divided by 2π satisfies: the remainder result Mod(φ, 2π) of the target phase φ at the aperture position where the metasurface lens is located in the unit structure where this unit structure is located divided by 2π, that is: Mod(Φ, 2π) = Mod(φ, 2π); And, The compensation phase ΔΦ of each unit structure corresponds to the achromatic band [λ1, λ2] λ1-λ2 , and the target phase difference Δφ of the metasurface lens corresponding to the achromatic band [λ1, λ2] at the aperture position where the unit structure is located λ1-λ2 Satisfy: ΔΦ λ1-λ2 =Δφ λ1-λ2 。 8. The design method according to claim 7, wherein, The target phase of the metasurface lens corresponding to any wavelength λ in the target achromatic band at the aperture position where any unit structure is located Satisfies: , and represent the coordinate positions of the aperture position in a rectangular coordinate system with the aperture center as the origin, represents the focal length of the metasurface lens.

9. The design method according to claim 6, wherein Before providing the lens substrate, it further includes: According to the pre-determined target phase difference distribution range, at least two unit families are created, where: The four-quadrant symmetric structure feature of the first unit family is configured such that: the compensation phase value range of the first unit family includes multiple discrete range segments spanning the target phase difference distribution range; The four-quadrant symmetric structure feature of the second unit family is configured such that: the compensation phase value range of the second unit family fills the vacancy formed by the discrete range segments of the first unit family in the first discrete distribution interval; The four-quadrant symmetric structure feature of the third unit family is configured such that: the compensation phase value range of the third unit family fills the vacancy formed by the discrete range segments of the first unit family in the second discrete distribution interval; Among them, the upper limit of the absolute value of the compensation phase in the second discrete distribution interval is less than the lower limit of the absolute value of the compensation phase in the first discrete distribution interval.

10. The design method according to claim 9, characterized in that, Before providing the lens substrate, it further includes: Performing finite element analysis on each unit structure in the at least two unit families created; According to the analysis value of the finite element analysis and the pre-set target transmittance of the unit structure, determine the height dimension of each unit structure in the at least two unit families in the direction perpendicular to the lens substrate, and the period between each unit structure and the adjacent unit structure after each unit structure is selected.

Images