CN115657303A - Design method of dual-cascade metalens and long-wave infrared metalens imaging system - Google Patents

Abstract

The invention discloses a design method of a dual-cascade meta-lens and a long-wave infrared meta-lens imaging system, belonging to the field of lenses and micro-nano photonics. The method includes: calculating columnar structural units with different radii by using a strict coupled wave analysis method The phase mutation introduced when the long-wave infrared characteristic wavelength is incident, and the dispersion distribution in the long-wave infrared, multiple sets of radius-phase mutation-dispersion distribution are obtained to form a columnar structural unit library; so that the double-cascaded meta-lens can be used for incident light The goal is to control the wavefront and correct the high-level aberration of the incident light, and determine the target phase distribution of the periodic array of hexagonal lattices on the metasurface; according to the target phase distribution, the goal is to have the highest consistency in the dispersion distribution of each hexagonal lattice in the same metasurface , and determine the radius of the columnar structural unit at each hexagonal lattice from the selected results. Using a special dispersion design method, the meta-optical element can be used in the field of infrared large-aperture imaging applications.

Description

Design method of dual-cascade metalens and long-wave infrared metalens imaging system

technical field

The invention belongs to the field of lenses and micro-nano photonics, and more specifically relates to a design method of a double-cascaded meta-lens and a long-wave infrared meta-lens imaging system.

Background technique

In order to achieve high-performance and high-quality imaging effects, traditional infrared optical imaging systems often inevitably use multiple refractive lenses, making the system bulky and heavy, which is in line with the current development needs of planar, miniaturized, and lightweight optical systems. Run in the opposite direction. In recent years, when the metasurface lens that has received much attention is used for focusing imaging, it is often accompanied by huge chromatic aberration, and parameters such as numerical aperture, field angle, and aperture are mutually limited. Using a metasurface lens alone still cannot achieve the same level as the traditional lens group. image quality.

The composite optical system based on the metasurface lens can better solve the above problems. For example, the patent CN110488394A provides a long-wave infrared composite optical system, which simplifies the structure of the optical system and optimizes the processing technology. However, the existing composite optical system based on metasurface lenses ignores the problem of inconsistent dispersion performance of metasurfaces under the two algorithm models when the metasurface element design algorithm is combined with the traditional optical element design optimization algorithm. As a result, the actual imaging effect of the optical system cannot reach the expected effect of simulation.

Contents of the invention

Aiming at the defects and improvement needs of the prior art, the present invention provides a design method of a double cascaded metalens and a long-wave infrared metalens imaging system, the purpose of which is to solve the problem of the existing joint metasurface element design algorithm and traditional optical When designing the optimization algorithm for the element, the problem of inconsistent dispersion performance of the metasurface under the two algorithm models was ignored.

In order to achieve the above object, according to one aspect of the present invention, a design method of a double-cascaded metalens is provided. The double-cascaded metalens is used in a long-wave infrared metalens imaging system, including a dielectric substrate layer and a The metasurface on both sides of the dielectric substrate layer, the metasurface is formed by a plurality of columnar structural units arranged in a periodic array of hexagonal lattices, the method includes: S1, using the strict coupled wave analysis method to calculate the columnar structural units with different radii The phase mutation introduced when the long-wave infrared characteristic wavelength is incident, and the dispersion distribution in the long-wave infrared, multiple groups of corresponding radius-phase mutation-dispersion distribution are obtained to form a columnar structural unit library; S2, so that the double cascade The metalens can regulate the wavefront of the incident light and correct the high-level aberration of the incident light, and determine the target phase distribution of the metasurface hexagonal lattice periodic array; S3, for any hexagonal lattice, according to the For the target phase of the hexagonal lattice, select multiple groups of radius-phase abrupt change-dispersion distribution corresponding to the phase mutation from the columnar structural unit library; The target is to determine the radius of the columnar structural unit at each hexagonal lattice from the results selected in S3.

Furthermore, the radius of the columnar structural unit in S1 satisfies: the phase mutation corresponding to all radii covers 0-2π.

Furthermore, for columnar structural units of any radius, the calculation of its dispersion distribution in the long-wave infrared in the S1 includes: calculating the phase mutation introduced by the columnar structural units of any radius when the maximum wavelength of the long-wave infrared is incident, and the long-wave infrared The phase mutation introduced when the infrared minimum wavelength is incident; the difference between the phase mutation corresponding to the maximum wavelength and the phase mutation corresponding to the minimum wavelength is calculated to obtain the dispersion distribution.

According to another aspect of the present invention, a long-wave infrared metalens imaging system is provided, including: a first lens group, a double cascaded superlens, and a second lens group arranged in sequence along the optical axis from the object side to the image side and an infrared focal plane detector, the double-cascaded metalens is obtained by the design method of the double-cascaded metalens as described above.

Furthermore, the focal lengths of the two metasurfaces of the double-cascaded metalens and the focal length of the long-wave infrared metalens imaging system satisfy:

f ₁ /f>10

f ₂ /f>10

Wherein, f ₁ is the focal length of a metasurface of the dual-cascade metalens, f ₂ is the focal length of the other metasurface of the dual-cascade metalens, and f is the focal length of the long-wave infrared metalens imaging system .

Furthermore, the first lens group includes a first lens and a second lens, the second lens group includes a third lens and a fourth lens, and the first lens, the second lens, and the double cascaded superstructure lens , the third lens and the fourth lens are sequentially arranged along the optical axis from the object side to the image side; the first lens is a negative lens, and the second lens, the third lens and the fourth lens are positive lenses; Both the negative lens and each of the positive lenses are used to correct the primary aberration of the incident light and focus the light before emitting it.

Furthermore, the height of each columnar structural unit in the metasurface of the double-cascade metalens is the same, and the height is in the order of the detected infrared wavelength, and the radius is in the order of sub-wavelength.

Furthermore, in the metasurface of the double-cascaded metalens, the materials of the columnar structure unit and the dielectric substrate layer are both intrinsic single crystal silicon.

Furthermore, the infrared focal plane detector includes a detector window and an infrared focal plane array arranged in sequence along the optical axis; the material of the first lens group, the second lens group and the detector window is germanium , one or any combination of barium fluoride, zinc sulfide, zinc selenide, AMTIR, IG, IRG.

Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:

(1) Provide a design method for double-cascaded metalenses, use rigorous coupled wave analysis to solve the dispersion distribution of columnar structural units in the long-wave infrared, introduce a library of columnar structural units with phase mutations covering all 2π, and select dispersion from them The distribution of columnar structural units with high consistency is used to form a double-cascaded metalens, which effectively ensures that the actual phase distribution function of the metalens is in good agreement with the high-order even-order polynomial function, and reduces the distortion of the metalens itself due to dispersion. The influence of focal length drift on the imaging quality of the system;

(2) The phase distribution function of the metasurface of the dual-cascade metalens adopts a high-order even-order polynomial form. On the one hand, it increases the degree of freedom for system optimization and is conducive to achieving better imaging quality. The polynomial form can be quickly optimized by ray tracing method and damped least squares method, compatible with the rapid optimization method of traditional lens groups, and suitable for the design and solution of compound optical systems;

(3) A long-wave infrared metalens imaging system is provided, which uses traditional refractive lenses to correct primary aberrations, uses double cascaded metalenses to finely regulate the wavefront of light, corrects advanced aberrations of the system, and uses refractive lenses and The structure combined with the metalens realizes the integration with the small pixel and the large array infrared focal plane array, achieving high-resolution infrared detection imaging, and the modulation transfer function reaches the diffraction limit, and the imaging quality is good;

(4) Since the metalens element replaces multiple traditional refracting lenses, the structure of the optical system can be simplified. At the same time, the processing technology of the metasurface is compatible with the semiconductor technology. Constructed lenses entered the device-level application market.

Description of drawings

Fig. 1 is a flow chart of the design method of the dual-cascade metalens provided by the embodiment of the present invention;

2 is a schematic structural diagram of a long-wave infrared metalens imaging system provided by an embodiment of the present invention;

3 is a schematic diagram of ray tracing at a central wavelength of 10 μm of the long-wave infrared metalens imaging system provided by the embodiment of the present invention;

Figure 4A and Figure 4B are the phase distribution functions required to be achieved by the first metasurface and the second metasurface of the dual-cascade metalens provided by the embodiment of the present invention, respectively;

FIG. 5 is a diagram of light spots at the photosensitive surface of the simulated infrared focal plane array provided by the embodiment of the present invention;

FIG. 6 is a simulated MTF curve diagram provided by an embodiment of the present invention;

Fig. 7 is a schematic diagram of simulated field curvature and distortion provided by an embodiment of the present invention;

Fig. 8 is a simulation imaging effect diagram provided by an embodiment of the present invention;

Fig. 9A is a schematic diagram of a columnar structural unit provided by an embodiment of the present invention;

Fig. 9B is a top view of the columnar structural unit provided by the embodiment of the present invention;

Fig. 10 is a schematic diagram of phase change and transmittance obtained by columnar structural units with different diameters provided by an embodiment of the present invention;

Fig. 11 is a schematic diagram of the reference phase at the central wavelength and the relative dispersion in the working band of columnar structural units with different diameters provided by the embodiment of the present invention;

Fig. 12 is a schematic structural diagram of a double cascaded metalens provided by an embodiment of the present invention;

Figure 13A is the near-field phase distribution profile and phase distribution grayscale diagram of the non-dispersion management, small-aperture single-wavelength focusing metalens under different incident wavelengths provided by the embodiment of the present invention

Fig. 13B is a near-field phase distribution profile and phase distribution grayscale diagram of the dispersion management, small-aperture single-wavelength focusing metalens under different incident wavelengths provided by the embodiment of the present invention.

Throughout the drawings, the same reference numerals are used to designate the same elements or structures, wherein:

1 is the first lens, 2 is the second lens, 3 is the double cascaded metalens, 301 is the first metasurface, 302 is the second metasurface, 303 is the dielectric substrate layer, 4 is the third lens, 5 is the second metasurface Four lenses, 6 is an infrared focal plane detector, 601 is a detector window, 602 is an infrared focal plane array, and 7 is a columnar structural unit.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

In the present invention, the terms "first", "second" and the like (if any) in the present invention and drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

FIG. 1 is a flow chart of a design method of a dual-cascade metalens provided by an embodiment of the present invention. Referring to FIG. 1 , in conjunction with other drawings, the design method of the dual-cascade metalens in this embodiment will be described in detail. The method includes operation S1-operation S4.

The dual-cascade metalens is used in the long-wave infrared metalens imaging system, as shown in Figure 2. The double-cascaded metalens includes a dielectric substrate layer 303 and metasurfaces located on both sides of the dielectric substrate layer. The metasurface is formed by a plurality of columnar structural units 7 arranged in a periodic array of hexagonal lattices, as shown in FIG. 12 . Preferably, the metasurfaces on both sides of the dielectric substrate layer are plane, and the thickness of the dielectric substrate layer is 0.6 mm. In this embodiment, the radius of each columnar structural unit in the metasurface is designed to reduce the influence of the focal length drift of the dual-cascade metalens itself due to dispersion on the imaging quality of the system.

Operate S1 and use the strict coupled wave analysis method to calculate the phase mutation introduced by the columnar structural units with different radii when the characteristic wavelength of the long-wave infrared is incident, and the dispersion distribution in the long-wave infrared, and obtain multiple sets of radius-phase mutation-dispersion distribution corresponding to each other , to form a library of columnar structural units.

According to an embodiment of the present invention, for a columnar structural unit with any radius, calculating its dispersion distribution in the long-wave infrared in operation S1 includes: calculating the phase abrupt change introduced by the columnar structural unit with any radius when the maximum wavelength of long-wave infrared is incident, And the phase mutation introduced when the minimum wavelength of the long-wave infrared is incident; the difference between the phase mutation corresponding to the maximum wavelength and the phase mutation corresponding to the minimum wavelength is calculated to obtain the dispersion distribution.

According to an embodiment of the present invention, the radius of the columnar structural unit selected in operation S1 satisfies: in the columnar structural unit library, the phase mutations corresponding to all radii cover 0-2π. The phase mutation covering 0-2π means that for any phase mutation within the range of 0-2π, there is one or more corresponding to the radius.

In this embodiment, assuming that the radius of the columnar structural unit is selected in the interval of (d1, d2), this interval can be divided into several sub-intervals, and in each sub-interval, the phase mutation increases with the increase of the radius, and the sub-interval The phase mutation in the interval covers 0-2π, thus, any phase mutation within the range of 0-2π has several corresponding radii corresponding to it.

即为参考相位，最大波长12μm下的相位突变与最小波长10μm下的相位突变之间的差值即为色散分布D，基于此，得到一组对应的半径d-相位突变

-色散分布D。多次选取新的半径d，重复上述操作，即可得到多组半径d-相位突变

-色散分布D，组成柱状结构单元库，如图11所示。Taking the radius d, the characteristic wavelength of long-wave infrared as 10 μm, the minimum wavelength of long-wave infrared as 8 μm, and the maximum wavelength of long-wave infrared as 12 μm as an example, in operation S1, use the rigorous coupled wave analysis method to calculate the columnar structural units with a radius of d at 8 μm , Phase change at 10μm, 12μm, phase change at characteristic wavelength 10μm

It is the reference phase, and the difference between the phase mutation at the maximum wavelength of 12 μm and the phase mutation at the minimum wavelength of 10 μm is the dispersion distribution D. Based on this, a set of corresponding radius d-phase mutations is obtained

- Dispersion distribution D. Select a new radius d multiple times and repeat the above operation to obtain multiple sets of radius d-phase mutation

- Dispersion distribution D, forming a library of columnar structural units, as shown in FIG. 11 .

Referring to Figure 11, each data point in the figure corresponds to a columnar structural unit with a specific radius. The value of the abscissa of this point reflects the corresponding phase mutation, and the value of the ordinate reflects the corresponding dispersion distribution. For example, the data point at the origin represents the radius The phase change and dispersion distribution of the columnar structural units with a diameter of 0 nm are 0.

In operation S2, aiming at enabling the double-cascaded metalens to regulate the wavefront of the incident light and correct the high-level aberration of the incident light, determine the target phase distribution of the periodic hexagonal lattice array on the metasurface.

满足如下表达式：Along the optical axis, the two metasurfaces of the double cascaded metalens are respectively defined as the first metasurface 301 and the second metasurface 302, and the first metasurface and the second metasurface are respectively composed of micro Structure array configuration, phase distribution of two microstructure arrays

Satisfy the following expression:

Among them, ρ is the radial coordinate of the metasurface, R is the normalized radius, A _n , B _n , C _n , and D _n are the polynomial coefficients of the nth metasurface, n=1,2.

Specifically, in operation S2, with the goal of enabling the double-cascaded metalens to control the wavefront of the incident light and correct the high-level aberration of the incident light, the R, A _n , B _n , C _n , D _n are optimized, for example see Table 1 for specific values, so as to determine the target phase distribution of the hexagonal lattice periodic arrays of the first metasurface and the second metasurface. The schematic diagram of the ray tracing of the optical system is shown in Figure 3. The phase distribution diagram of the optimized first metasurface microstructure array is shown in FIG. 4A , and the phase distribution diagram of the second metasurface microstructure array is shown in FIG. 4B .

Table 1

R(mm) A_n B_n C_n D_n first metasurface 100.031 -3929.457 -3.518e+5 1.505e+6 -4.972e+6 second metasurface 100.000 2717.567 3.558e+5 -1.557e+6 5.273e+6

In operation S3, for any hexagonal lattice, according to the target phase of the hexagonal lattice, multiple sets of radius-phase abrupt change-dispersion distribution corresponding to the phase abrupt change are selected from the columnar structural unit library.

和相位突变

之间具有一一对应的关系，一个相位突变

会对应多个半径。基于此，对于任一六方晶格，根据其目标相位，可以从柱状结构单元库中选取相应的多组半径-相位突变-色散分布，这多组半径-相位突变-色散分布的相位突变相同且与该六方晶格的目标相位相对应。target aspect

and phase breaks

There is a one-to-one correspondence between them, a phase mutation

Will correspond to multiple radii. Based on this, for any hexagonal lattice, according to its target phase, corresponding multiple groups of radius-phase mutation-dispersion distributions can be selected from the columnar structural unit library, and the phase mutations of these multiple groups of radius-phase mutation-dispersion distributions are the same And correspond to the target phase of the hexagonal lattice.

In operation S4, aiming at the highest consistency of the dispersion distribution of each hexagonal lattice in the same metasurface, determine the radius of the columnar structural unit at each hexagonal lattice from the results selected in operation S3.

In this embodiment, operation S3 determines multiple sets of alternatives for the radius of the columnar structural unit at each hexagonal lattice. Operation S4 considers the dispersion distribution of all hexagonal lattices as a whole, with the goal of making the dispersion distribution most consistent everywhere, and determines the corresponding optimal solution for the radius of the columnar structural unit at each hexagonal lattice (optimal radius-phase mutation-dispersion distribution), the radius in the optimal scheme is determined as the radius of the columnar structural unit at the corresponding hexagonal lattice.

In this embodiment, the schematic diagram of the columnar structural unit is shown in Figure 9A, and the top view is shown in Figure 9B. The parameters such as the radius, height, and array period of the columnar structural unit are optimized by using the vector electromagnetic field numerical simulation algorithm, and the parameters of the radius and phase are obtained. relation. The phase change and transmittance of the columnar structural unit at different radii are shown in Figure 10. The height of the optimized columnar structural unit is 8 μm, and the period of the columnar structural unit is 3 μm.

The design method of the dual-cascade metalens in the embodiment of the present invention solves the problem of the complex structure of the traditional optical system, the short imaging distance of the small-aperture metalens, the poor wide-spectrum imaging effect of the large-aperture metalens element, and the combination of metasurface elements and traditional optics. The technical problem of incompatibility of component design optimization algorithms; by adopting a special dispersion management method, a design method of a large-aperture meta-lens is provided to ensure that the large-aperture meta-surface lens is used in ray tracing calculations and electromagnetic time-domain finite difference calculations The performance is consistent; the meta-optical element enters the field of infrared large-aperture imaging applications.

The embodiment of the present invention also provides a long-wave infrared metalens imaging system, including: a first lens group, a double cascaded metalens 3, a second lens group and an infrared The focal plane detector 6 and the double-cascade metalens are obtained by the design method of the above-mentioned double-cascade metalens. The structure of the system is shown in FIG. 2 .

The long-wave infrared metalens imaging system uses traditional refraction lenses to correct primary aberrations, uses double cascaded metalenses to fine-tune the wavefront of light, corrects advanced aberrations of the system, and simplifies the structure of the optical system while ensuring imaging quality. For example, the system is oriented to imaging in the long-wave infrared band with a center wavelength of 10 μm. The image plane angle height of the system is 27.376 mm, the aperture number is 0.800, and the total system length is less than 150 mm.

According to an embodiment of the present invention, the height of each columnar structure unit in the metasurface of the dual-cascade metalens is the same, and the height is in the order of the detected infrared wavelength, and the radius is in the order of sub-wavelength. The double-cascade metalens is used to regulate the wavefront of the incident light, and realize the correction of the advanced aberration of the incident light before exiting.

According to an embodiment of the present invention, the focal length of the two metasurfaces of the dual-cascade metalens and the focal length of the long-wave infrared metalens imaging system satisfy:

f ₁ /f>10

f ₂ /f>10

Among them, f ₁ is the focal length of one metasurface of the dual-cascade metalens, f ₂ is the focal length of the other metasurface of the dual-cascade metalens, and f is the focal length of the long-wave infrared metalens imaging system. Preferably, in this embodiment, f=25.006, f ₁ =1000.001, f ₂ =1000.001, f ₁ /f=40, f ₂ /f=40.

By designing f ₁ , f ₂ , and f as above, the metasurface can bear a certain optical power in the optical system, reduce the pressure of the refraction lens on the light focusing, and transfer the tolerance limit of the refraction lens processing to the metasurface , which is beneficial to reduce the tolerance sensitivity of the system. At the same time, the focal length of each metasurface is an order of magnitude larger than the focal length of the imaging system, which avoids the excessive optical power of the metasurface in the optical system, and effectively guarantees the optimization of the ray tracing algorithm and the damped least squares method in the simulation design. went well.

According to an embodiment of the present invention, in the metasurface of the dual-cascade metalens, the materials of the columnar structural unit and the dielectric substrate layer are both intrinsic single crystal silicon.

According to an embodiment of the present invention, the infrared focal plane detector includes a detector window 601 and an infrared focal plane array 602 arranged in sequence along the optical axis. The detector window is used to filter the stray light of the system and light outside the detection band, and the infrared focal plane array is used to detect and image the focused infrared light incident light.

Preferably, the pixel interval of the infrared focal plane array is 5 μm-17 μm, and the number of pixels or the resolution is 1280×960. Further, the pixel interval of the infrared focal plane array is 17 μm, and the center wavelength is 10 μm. The detector window is made of infrared germanium glass material.

The materials of the first lens group, the second lens group and the detector window are one or any combination of germanium, barium fluoride, zinc sulfide, zinc selenide, AMTIR, IG and IRG. It should be noted that the first lens group, the second lens group and the detector window can also use other materials that can transmit long-wave infrared.

The first lens group includes the first lens 1 and the second lens 2, the second lens group includes the third lens 4 and the fourth lens 5, the first lens 1, the second lens 2, the double cascaded metal lens 3, the third lens The lens 4, the fourth lens 5, and the infrared focal plane detector 6 are sequentially arranged along the optical axis from the object side to the image side.

The first lens is a negative lens, the second lens, the third lens and the fourth lens are positive lenses; the negative lens and each positive lens are used to correct the primary aberration of the incident light and focus the light before exiting, the incident light The wavelength is in the infrared band.

Preferably, the refractive surfaces of the first lens, the second lens, the third lens and the fourth lens adopt an even-order aspheric surface, the material of the first lens and the third lens is infrared germanium glass, and the material of the second lens and the fourth lens IRG207 chalcogenide glass material.

Combined with Figure 3, the detailed structural parameters of the first lens, the second lens, the third lens, and the fourth lens are optimized and determined by using the ray tracing method and the damped least squares method. See Table 2 and Table 3 for specific values.

Table 2

table 3

FIG. 5 is a spot diagram at the photosensitive surface of the infrared focal plane array simulated by the imaging system in this embodiment. The diameters of the imaging spots of the on-axis field of view, the zone field of view and the peripheral field of view are all smaller than the pixel interval of the infrared focal plane array. This means that in this embodiment, the optical imaging resolution in the full field of view is higher than the resolution of the infrared focal plane array, that is, it is verified that the embodiment of the present invention can realize high-resolution infrared imaging in the full field of view.

FIG. 6 is a simulated MTF curve of the imaging system in this embodiment. At the cut-off frequency of the infrared focal plane detector is 30 lp/mm, the MTF of the full field of view is MTF>0.6, which is close to the diffraction limit. FIG. 7 is a field curvature and distortion diagram simulated by the imaging system in this embodiment. The imaging module has barrel distortion, and the relative distortion of the full field of view is less than 25%. FIG. 8 is a simulated imaging diagram of the imaging system in this embodiment, indicating that the imaging system can realize high-resolution infrared imaging.

Further, in order to illustrate that selecting a columnar structural unit with high dispersion consistency can make the dispersion performance of the double-cascade metalens consistent in the traditional optical element design optimization algorithm and in the metasurface element design algorithm, the same method as in this embodiment is adopted. In the following steps, conventional columnar structural units and high-dispersion uniform structural units are selected for periodic discretized arrangement to construct two kinds of small-aperture single-wavelength focusing superlenses with a working wavelength of 10 μm. Figure 13A and Figure 13B respectively show the two The near-field phase distribution profiles and grayscale images of the back surface of the metasurface focusing lens calculated by using the finite-difference time-domain algorithm under the incident light of 8 μm, 10 μm, and 12 μm. The phase profile curves in the figure have been normalized to represent different The relative phase at the location relative to the center. Due to the poor consistency of the dispersion distribution of the columnar structural units with different phase mutations, the near-field phase distribution changes with the wavelength of the incident light in the metalenses constructed by selecting conventional columnar structural units. Due to the similar dispersion of the columnar structure with different phase mutations, the near-field phase distribution does not change with the wavelength of the incident light. The dispersion performance is the same as the even-order coefficient phase distribution optimized by the ray tracing algorithm and damped least squares method in this embodiment. The polynomials are the same, that is, the dispersion performance of the metalens is consistent in the traditional optical element design optimization algorithm and the metasurface element design algorithm.

In the embodiment of the present invention, the traditional lens structure of a large number of lenses is replaced by introducing metasurface elements (i.e. double cascaded metalenses), so that the imaging system tends to be miniaturized and lightweight. At the same time, by combining traditional lens groups, the system The optical power is mainly allocated to the traditional refractive lens, which makes up for the shortcomings of the large-aperture meta-lens in the wide-spectrum work when it is used alone for imaging, and makes the large-aperture meta-lens enter the field of infrared broadband imaging applications; secondly, for The metasurface element adopts the form of double cascading, which doubles the number of optimization parameters, expands the optimization solution space enough to achieve the design goal, and strengthens the correction effect on advanced aberrations and off-axis aberrations, which is conducive to the optimization of the system. field of view characteristics. Furthermore, the phase distribution of the metasurface microstructure array is in the form of a high-order even-order polynomial, which further expands the optimization solution space and further increases the number of optimization parameters to achieve the design goal, and this phase distribution form is convenient to use ray tracing Trace method and damped least square method are used for rapid optimization, compatible with traditional lens group optimization algorithms, and suitable for the overall design of compound optical systems. In addition, according to the working band of the long-wave infrared metalens imaging module, the dispersion distribution of the periodic micro-nano structural unit in this band is solved by using the strict coupled wave analysis method, and the introduced phase mutation is selected to cover the full 2π, and the dispersion distribution remains relatively consistent. The columnar structural unit constitutes a library of columnar structural units, and a periodic array of structural arrangements is selected from it to effectively ensure that the actual phase distribution function of the metalens is in good agreement with the high-order even-degree polynomial function. Finally, the integration of infrared imaging optical system with small pixel and large array of infrared focal plane detectors is realized, high-resolution infrared detection imaging is achieved, and the modulation transfer function of the optical system reaches the diffraction limit.

To sum up, the long-wave infrared metalens imaging system in the embodiment of the present invention uses a double cascaded metalens to regulate the wavefront of the incident light, and realizes aberration elimination together with the traditional lens group. By selecting a columnar structural unit with high dispersion consistency, the metalens is suitable for large-aperture optical imaging systems; and the integration with small pixels and large array infrared focal plane detectors is realized by using a simple lens structure, achieving high Resolution infrared detection imaging; modulation transfer function reaches the diffraction limit. It has the characteristics of simple structure, low cost, high resolution and good imaging quality.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (9)

1. A design method of a double-cascade super-structured lens is characterized in that the double-cascade super-structured lens is used for a long-wave infrared super-structured lens imaging system and comprises a medium substrate layer and super surfaces positioned on two sides of the medium substrate layer, the super surfaces are formed by arraying a plurality of columnar structure units according to a hexagonal lattice period, and the method comprises the following steps:

s1, calculating phase mutation introduced by columnar structure units with different radiuses when the columnar structure units enter at a long-wave infrared characteristic wavelength and dispersion distribution at a long-wave infrared characteristic wavelength by using a strict coupled wave analysis method to obtain a plurality of groups of mutually corresponding radius-phase mutation-dispersion distribution so as to form a columnar structure unit library;

s2, determining target phase distribution of the super-surface hexagonal lattice periodic array by taking the double cascade super-structure lens as a target, wherein the double cascade super-structure lens can perform wavefront regulation on incident light and correct high-order aberration of the incident light;

s3, for any hexagonal lattice, selecting a plurality of groups of radius-phase mutation-dispersion distributions with corresponding phase mutations from the columnar structural unit library according to the target phase of the hexagonal lattice;

and S4, determining the radius of the columnar structure unit at each hexagonal lattice from the result selected in the S3 by taking the highest dispersion distribution consistency of all hexagonal lattices in the same super surface as a target.

2. The method of designing a double cascade metamaterial lens as claimed in claim 1, wherein the radius of the pillar-shaped structural unit in S1 satisfies: all radii correspond to phase jumps covering 0-2 pi.

3. The method for designing a double cascade superstructure lens according to claim 1 or 2, wherein calculating the dispersion profile in the long wavelength infrared in S1 for a cylindrical structural unit of any radius comprises:

calculating the phase jump introduced by the columnar structure unit with any radius when the long-wave infrared maximum wavelength is incident and the phase jump introduced when the long-wave infrared minimum wavelength is incident;

and calculating the difference value between the phase jump corresponding to the maximum wavelength and the phase jump corresponding to the minimum wavelength to obtain the dispersion distribution.

4. A long wave infrared super structure lens imaging system, comprising: the first lens group, the double-cascade super-structure lens, the second lens group and the infrared focal plane detector are sequentially arranged from an object side to an image side along an optical axis, and the double-cascade super-structure lens is obtained by the design method of the double-cascade super-structure lens as claimed in any one of claims 1 to 3.

5. The long-wave infrared metamaterial lens imaging system of claim 4, wherein the focal lengths of the two metasurfaces of the dual cascaded metamaterial lens and the focal length of the long-wave infrared metamaterial lens imaging system satisfy:

f ₁ /f>10

f ₂ /f>10

wherein f is ₁ A focal length of a super surface of the double cascade super-structured lens，f ₂ And f is the focal length of the other super surface of the double cascade super structure lens, and f is the focal length of the long-wave infrared super structure lens imaging system.

6. The longwave infrared metamaterial lens imaging system of claim 4, wherein the first lens group includes a first lens and a second lens, the second lens group includes a third lens and a fourth lens, the first lens, the second lens, the double cascade metamaterial lens, the third lens, and the fourth lens are arranged in order along the optical axis from the object side to the image side;

the first lens is a negative lens, and the second lens, the third lens and the fourth lens are positive lenses; the negative lens and each positive lens are used for correcting the primary aberration of incident light, focusing light and emitting the light.

7. The long-wave infrared metamaterial lens imaging system of claim 4, wherein the height of each columnar structure unit in the super-surface of the dual cascaded metamaterial lens is the same, and the height is on the order of the detected infrared wavelength and the radius is on the order of the sub-wavelength.

8. The long-wave infrared metamaterial lens imaging system of claim 4, wherein in the metasurface of the dual cascaded metamaterial lens, the columnar structure elements and the dielectric substrate layer are both intrinsic single crystal silicon.

9. The long-wave infrared meta-lens imaging system of any of claims 4 to 8, wherein the infrared focal plane detector comprises a detector window and an infrared focal plane array sequentially disposed along an optical axis;

the materials of the first lens group, the second lens group and the detector window are one or any combination of germanium, barium fluoride, zinc sulfide, zinc selenide, AMTIR, IG and IRG.

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