Achromatic method for infrared optical system and infrared optical system thereof

Abstract

The application relates to an achromatic method of an infrared optical system and the infrared optical system. The achromatic method of the application, wherein the infrared optical system comprises a refractive lens and a super lens arranged in sequence from an object side to an image side, the method comprises the following steps: acquiring a phase distribution and a light transmittance distribution of nano atoms in a size change range of the nano atoms; determining a phase profile curve of a binary surface type of the super lens, then acquiring setting parameters of nano atoms of the super lens, and after the setting parameters of the nano atoms of the super lens are acquired, performing a FDTD simulation experiment, acquiring a focusing efficiency of the infrared optical system, and using the focusing efficiency to optimize parameters of the infrared optical system to improve achromatic effects of the infrared optical system. The achromatic method of the infrared optical system has the advantages of high focusing efficiency and good imaging quality, and can realize good focusing imaging in an 8-12 um wave band.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of infrared optical technology, in particular to an achromatic method of an infrared optical system and the infrared optical system. BACKGROUND

[0002] In the field of modern infrared imaging applications, it is often necessary to achieve good focusing of the optical system within a certain wavelength bandwidth, that is, the long-wave infrared optical system needs to achieve achromatic function, which is also an important indicator in high-quality optical systems.

[0003] In the traditional design of infrared imaging systems, there are mainly two ways to achieve achromatic effect: one method is to rely on the combination of optical glass materials, which actually uses two kinds of glass to combine a lens material that is conducive to achromatic effect, but this method often makes the optical system very complex, increases the volume, weight and cost of the system, and makes the error larger. The other method is to use a reflective optical system, which does not have dispersion effect, but the imaging quality is not high, the volume is large, the system is redundant, and the cost is high.

[0004] In recent years, the research on achromatic effect of superlens has developed quite a lot. For the realization of achromatic effect of superlens: one method is mainly to rely on the group delay and group delay dispersion characteristics of the nanometer atomic group of transmission type superlens components, the group delay of different sizes of atoms in this method will have different responses to different wavelengths, so it is necessary to have a library with a large number of nanometer atomic shapes and their corresponding responses, and then the nanometer atoms that meet the existing chromatic aberration curve in the optical system are obtained through manual or computer screening. However, due to the very large number of nanometer atoms, the screening efficiency is low, and even with the support of high-configuration computers, the step of screening nanometer atoms still needs a lot of time. Another method is to control the group delay of the nanometer atoms of P-B type superlens components by their own rotation angle to respond differently to different wavelengths, but this method realizes a polarization-dependent superlens infrared system, which is equivalent to sacrificing 50% of the focusing efficiency, so the focusing effect is not good.

[0005] At present, there are infrared optical systems formed by combining traditional lenses and superlenses in the prior art, such as the patent document with the application number CN202210646912.0, which relates to a superlens infrared lens, which includes a spherical mirror and a superlens, the superlens includes a substrate and three kinds of nanometer columns with C4 symmetry arranged on the substrate. However, the working wavelength of the superlens infrared lens is 10.6um, which cannot achieve achromatic effect within a certain infrared wavelength bandwidth. SUMMARY

[0006] Based on this, the purpose of the present application is to provide a method for achromatizing an infrared optical system, which has the advantages of good focusing imaging in the 8-12um waveband of the infrared optical system, high focusing efficiency, good imaging quality, small volume and light weight of the infrared optical system, etc.

[0007] A method for achromatizing an infrared optical system, wherein the infrared optical system comprises a refractive lens and a metasurface lens arranged in order from the object side to the image side, and the metasurface lens comprises a substrate and a plurality of nano atoms arranged on the surface of the substrate; the method comprises the following steps:

[0008] S1, obtaining the phase distribution and light transmittance distribution of the nano atoms within the size variation range of the nano atoms, and obtaining the phase profile curve of the binary surface type of the metasurface lens;

[0009] S2, obtaining the arrangement parameters of the nano atoms on the metasurface lens according to the phase distribution and light transmittance distribution of the nano atoms and the phase profile curve of the second lens;

[0010] S3, obtaining the optimized parameters of the infrared optical system according to the parameters of the infrared optical system and the arrangement parameters of the nano atoms on the metasurface lens obtained in step S2;

[0011] S4, FDTD simulation experiment, obtaining the focusing efficiency of the optimized infrared optical system;

[0012] S5, when the focusing efficiency is greater than or equal to a set threshold, the optimized parameters of the infrared optical system are output; when the focusing efficiency is less than a set threshold, the arrangement parameters of the nano atoms of the metasurface lens are adjusted, and the process returns to step S2 until the focusing efficiency is greater than or equal to the set threshold.

[0013] The method for achromatizing an infrared optical system disclosed in the present application can realize high light transmittance and accurate phase at corresponding positions of the metasurface lens by inversely optimizing the parameters of the nano atoms arranged on the surface of the metasurface lens according to the focusing efficiency of the infrared optical system, thereby realizing achromatization of the infrared optical system, improving the focusing efficiency of the infrared optical system, and achieving good focusing imaging in the 8-12um waveband.

[0014] Further, in step S5, after returning to step S2, the size of the nano atoms and the interval between adjacent two nano atoms are adjusted. By adjusting the size of the nano atoms and the interval between adjacent two nano atoms, the electric field coupling on the surface of the metasurface lens is reduced, thereby improving the focusing efficiency.

[0015] Further, the nano atoms include at least two of a nanoring column, a nanocylinder and a nanocube. In this scheme, the focusing effect is improved by using highly symmetrical nano atoms.

[0016] Further, the nanoring column has an inner diameter of 0.5-1 um and an outer diameter of 1.5-2 um, the nanocylinder has a radius of 0.5-2 um, and the nanocube has a radius of 1.5-4 um, and the nanoring column, the nanocylinder and the nanocube all have a height of 6 um.

[0017] Further, the adjustment of the size of the nano atoms and the interval between two adjacent nano atoms is specifically: the maximum radius of the nanocylinder and the nanoring column is less than 2 um, the maximum side length of the nanocube is less than 4 um, and the interval between two adjacent nano atoms is greater than or equal to 4 um.

[0018] Further, the interval between the refractive lens and the superlens is 4-10 mm.

[0019] Further, the interval between the refractive lens and the superlens is 10 um.

[0020] Further, the refractive lens is a double-aspheric positive lens, and the superlens has a negative dispersion effect. In this scheme, the positive dispersion effect of the refractive infrared optical lens is matched with the negative dispersion effect of the superlens, which is more conducive to realizing the achromatism of the infrared optical system.

[0021] Further, the material of the first lens is zinc selenide, the substrate is barium fluoride, and the nano atoms are germanium.

[0022] In addition, the present application also provides an infrared optical system obtained by the above-mentioned achromatic method.

[0023] In order to better understand and implement, the present application is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a structural schematic diagram of the infrared optical system of the present application;

[0025] Figure 2 is a structural schematic diagram of the present application Figure 1 is an enlarged schematic diagram of the structure at A in the present application;

[0026] Figure 3 is a structural schematic diagram of the basic structural unit containing nano atoms of the present application;

[0027] Figure 4 is a flowchart of the achromatic method of the infrared optical system of the present application;

[0028] Figure 5 Phase distribution and light transmittance distribution of the nanorings under different sizes of the present application, wherein, Figure 5 (a) is the phase distribution of the nanorings under different sizes, Figure 5 (b) is the light transmittance distribution of the nanorings under different sizes;

[0029] Figure 6 Phase profile curve and residual error diagram in a specific embodiment of the present application;

[0030] Figure 7 Superlens surface structure diagram in a specific embodiment of the present application and the corresponding electric field coupling change diagram before and after optimization by returning to step S2 from step S5 for optimization, wherein, Figure 7 (a) is a superlens surface diagram with nanometer atoms set, Figure 7 (b) is a spacing diagram between two adjacent nanometer atoms, Figure 7 (c) is a superlens electric field coupling diagram before optimization by returning to step S2 from step S5 for optimization, Figure 7 (d) is a superlens surface electric field coupling diagram after optimization by returning to step S2 from step S5 for optimization;

[0031] Figure 8 Imaging effect diagram of the infrared optical system obtained by the achromatic method of the present application in a specific embodiment of the present application, wherein, Figure 8 (a) is the spot diagram of the infrared optical system under 8, 10, 12um wavelength; Figure 8 (b) is the optical transfer function curve of the infrared optical system; Figure 8 (c) is the physical optical propagation spot diagram of the infrared optical system; Figure 8 (d) is the focal point displacement diagram of the infrared optical system with wavelength change;

[0032] Figure 9 Imaging effect of the infrared optical system obtained by the achromatic method of the present application under the condition that the distance between the first lens and the second lens is different; wherein, Figure 9 (a), Figure 9 (b), Figure 9 (c), Figure 9 (d) are respectively the imaging diagram of the infrared optical system obtained by the achromatic method of the present application and the corresponding spot diagram when the distance between the first lens and the second lens is 10mm, 8mm, 6mm, 4mm, Figure 9(e) the optical transfer function curve of the infrared optical system obtained by the achromatic method of the present application when the interval between the first lens and the second lens is 10 mm, 8 mm, 6 mm, and 4 mm;

[0033] Figure 10 The imaging data trend chart of the infrared optical system in Figure 9

[0034] Figure 11 The imaging schematic diagram of the infrared optical system of the present application. DETAILED DESCRIPTION

[0035] The present application provides an achromatic method of an infrared optical system, wherein the infrared optical system comprises a refractive lens and a superlens, and by using the optimized focusing efficiency of the infrared optical system, the parameters of the nanometer atoms arranged on the surface of the superlens are inversely optimized to realize high light transmittance and accurate phase of the superlens, and then realize achromatism of the infrared optical system, so that the infrared optical system can realize good focusing imaging in the 8-12um wave band, and the focusing efficiency is improved and the imaging quality is good.

[0036] Please refer to Figures 1-3 In the present application, the infrared optical system 10 comprises a first lens 11 and a second lens 12 arranged in sequence from the object side to the image side.

[0037] The first lens 11 is a refractive lens, which is a positive lens with double aspheric surfaces and has a positive dispersion effect.

[0038] For the material of the first lens 11, considering that the Abbe number of sulfide glass materials such as zinc selenide and zinc sulfide is smaller than that of germanium material, but the temperature coefficient, thermal conductivity and cost are relatively lower, therefore, in the present application, the material of the first lens 11 is preferably a sulfide glass material, such as zinc selenide and zinc sulfide. Further, since zinc selenide has lower thermal conductivity and wider working bandwidth than zinc sulfide, the material of the first lens 11 is more preferably zinc selenide.

[0039] The second lens 12 is a superlens, which has a negative dispersion effect. The superlens 12 comprises a planar substrate 121 and a plurality of nanometer atoms 122 arranged on one side surface of the substrate 121. The substrate 121 is made of barium fluoride material, and the nanometer atoms 122 are made of germanium material.

[0040] ​The nano atom 122 adopts a nano atom with high symmetry and high light transmittance, and preferably a nano atom with C4 symmetry, and specifically can be in the shape of a nano ring column, a nano cylinder, a nano square column, etc. The inner diameter of the nano ring column is 0.5-1 um, and the outer diameter is 1.5-2 um; the radius of the nano cylinder is 0.5-2 um; the side length of the nano square column is 1.5-4 um; and in order to effectively reduce the process difficulty of the super-structured lens in preparation, the height of the nano ring column, the nano cylinder and the nano square column is all 6 um. In the preferred scheme, the nano atom includes at least two kinds.

[0041] In addition, in the present application, the interval d between the first lens and the second lens can also be adjusted while the shape and the total optical length of the first lens 11 are basically kept unchanged. Specifically, the interval d between the first lens 1 and the second lens 2 is 4-10 mm, preferably 10 mm.

[0042] In the following, the achromatic method of the infrared optical system in the present application will be described. Please refer to Figure 4 The present application provides an achromatic method of an infrared optical system, specifically comprising the following steps:

[0043] S1, obtaining the phase distribution and light transmittance distribution of the nano atom 122 within the size variation range of the nano atom 122, and obtaining the phase profile curve of the binary surface type of the super-structured lens.

[0044] In the present application, different sizes of the nano atom 122 have different phase responses and light transmittance responses. For example, in Figure 5 In the present application, the phase and light transmittance of the nano ring column differ under different inner diameter sizes and outer diameter sizes. In addition, for the nano cylinder and the nano square column, the nano atom also has different phase responses and light transmittance responses under different sizes, and since the size of the nano cylinder and the nano square column only has one variable, the corresponding phase distribution and light transmittance distribution are both in the form of a curve.

[0045] In this step, the size variation range of the nano atom is as follows: the inner diameter variation range of the nano ring column is 0.5-1 um, and the outer diameter variation range is 1.5-2 um; the radius variation range of the nano cylinder is 0.5-2 um; the side length variation range of the nano square column is 1.5-4 um; and the height of the nano ring column, the nano cylinder and the nano square column is all 6 um.

[0046] In specific embodiments, optical software can be used to calculate the phase distribution and light transmittance distribution of the nano-atom 122 in a set size range of the nano-atom by scanning the basic structural unit with periodic boundary conditions on the substrate and by the finite-difference time-domain method for each shape of the single nano-atom. The structure of the basic structural unit can be seen from Figure 3 The basic structural unit includes the substrate 2 below and the nano-atom 122 placed in the center of the substrate surface, and the substrate 2 is the same as the substrate 121 of the superlens in material, thickness, etc.

[0047] Meanwhile, the phase profile curve representing the ideal phase of the superlens also needs to be obtained. Specifically, the superlens can be set as a binary surface by the optical design software, and the phase profile curve of the binary surface of the superlens can be obtained by the optical design software.

[0048] S2, according to the phase distribution and light transmittance distribution of the nano-atom, and the phase profile curve of the superlens, the setting parameters of the nano-atom on the superlens are obtained.

[0049] In the present application, according to the phase profile curve of the binary surface extracted by the optical design software, the shape of the nano-atom, the size of the nano-atom, the structural period of the nano-atom (i.e. the interval between two adjacent nano-atoms, such as Figure 7 d' represented in (b)), the lowest light transmittance, the phase error accuracy, etc. are selected until the actual phase curve of the superlens and the phase profile curve of the binary surface of the superlens 12 are fitted after the selected nano-atom is placed on the surface of the superlens. The setting parameters of the nano-atom 122 include the shape of the nano-atom, the setting position of the nano-atom on the superlens, the size of the nano-atom, the structural period of the nano-atom, the lowest light transmittance, the phase error accuracy, etc.

[0050] And in principle, the nano-atom with high phase accuracy and high light transmittance is preferred; in addition, in the selection process of the nano-atom, the lowest light transmittance and the phase error accuracy of the nano-atom of different shapes are different, and the numerical matching of the lowest transmittance and the phase error of the nano-atom is constantly optimized to realize the coverage of the nano-atom on the surface of the superlens.

[0051] Of course, in the selection process of the nano-atom, in the size range of each shape of the nano-atom, a plurality of nano-atoms of the same shape with different sizes can be selected.

[0052] In addition, in the fitting process, for the convenience of fitting, the actual phase curve of the superlens 12 and the phase profile curve of the binary surface type of the superlens 12 are simultaneously brought into the range of -π to π, as shown in Figure 6

[0053] S3, obtaining the optimized parameters of the infrared optical system according to the parameters of the infrared optical system and the setting parameters of the nano atoms on the superlens obtained in step S2.

[0054] In this step, through steps S1-S2, a setting mode of the nano atoms on the superlens of the infrared optical system is obtained, and then the setting parameters of the nano atoms determined in step S2 are replaced with the original setting parameters of the nano atoms in the infrared optical system, and the optimized parameters of the infrared optical system are obtained.

[0055] S4, FDTD simulation experiment is performed to obtain the focusing efficiency of the optimized infrared optical system.

[0056] In this step, FDTD simulation experiment is performed using the optimized parameters of the infrared optical system, and the focusing efficiency of the optimized infrared optical system is obtained.

[0057] S5, when the focusing efficiency is greater than or equal to a set threshold, the optimized parameters of the infrared optical system are output; when the focusing efficiency is less than a set threshold, step S2 is returned to adjust the setting parameters of the nano atoms 122 until the focusing efficiency is greater than or equal to the set threshold.

[0058] In this step, the infrared optical system is optimized using the focusing efficiency of the infrared optical system.

[0059] Specifically, when the focusing efficiency is greater than or equal to a set threshold, all the optimized parameters of the infrared optical system are output; when the focusing efficiency is less than a set threshold, step S2 is returned to adjust the setting parameters of the nano atoms 122 until the focusing efficiency is greater than or equal to the set threshold. In a specific embodiment, the set threshold can be 50%.

[0060] ​In the present application, the light transmittance and focusing efficiency of the superlens are low, which leads to low focusing efficiency of the infrared optical system. Therefore, it is found through research that the size of the nanoatom has a non-negligible influence on the transmittance and focusing efficiency of the superlens. Specifically, during the arrangement of the nanoatoms 122, the size of each nanoatom 122 is determined independently, and thus, when the nanoatoms 122 are arranged on the substrate 121, two or more nanoatoms with a size close to the structural period of the nanoatoms may be adjacent. As a result, during the simulation of the infrared optical system, the superlens may exhibit an electric field coupling phenomenon, which leads to low light transmittance and focusing efficiency of the superlens.

[0061] Therefore, in this step, during the process of returning to step S2 to optimize the parameters of the nanoatoms, a restriction condition is set for the size of the nanoatoms and the interval (i.e., the structural period of the nanoatoms) between two adjacent nanoatoms during the selection of the nanoatoms 122. Specifically, in the present application, the maximum radius of the nano-cylinders and nano-rings is set to be less than 2 um, the maximum side length of the nano-cubes is set to be less than 4 um, and the interval d' between two adjacent nanoatoms is set to be greater than or equal to 4 um, so as to eliminate the coupling effect between the nanoatoms.

[0062] In a specific embodiment, please refer to Figure 7 In Figure 7 In (a), the surface of the entire superlens 12 is provided with 900 nanoatoms arranged in a 30*30 matrix. During the simulation experiment in step S4, because two or more nanoatoms with a size close to the structural period of the nanoatoms are adjacent when the nanoatoms 122 are arranged on the substrate 121, the superlens 12 may exhibit a strong electric field coupling phenomenon, which leads to low focusing efficiency, as shown in (b). Figure 7 (c), where the electric field on the surface of the superlens 12 where the nanoatom with a larger size is located has a clear bright spot, which indicates that the electric field is localized in the nanoatom with a larger size during the propagation of the light field and does not propagate forward. By using the above achromatic method of the present application, the size of the nanoatoms is adjusted and the interval d' between two adjacent nanoatoms is set to be greater than or equal to 4 um, and the nanoatoms are selected again until the actual phase curve of the superlens is fitted with the phase profile curve of the binary surface of the superlens 12 after the selected nanoatoms are placed on the surface of the superlens, so as to optimize the parameters of the nanoatoms. As shown in Figure 7(d)It can be seen that after returning to step S2 to optimize the nano-atom parameters, the bright spots of the surface electric field of the super lens 12 are significantly reduced, that is, the number of large intensity coupling positions on the surface of the super lens 12 is significantly reduced, the mutual influence between the nano-atoms is significantly weakened, and the electric field coupling phenomenon is weakened. Moreover, after returning to step S2 to optimize the nano-atom parameters in step S5, the focusing efficiency obtained by the simulation experiment of the corresponding infrared optical system is compared with the focusing efficiency of the original infrared optical system. Under the 0° field of view, the focusing efficiency under the wavelengths of 8 um and 10 um can be increased to 48.5%.

[0063] In the present application, the infrared optical system obtained by the achromatic method of the present application is subjected to optical tracing simulation experiment in optical software, and an image quality evaluation index is obtained. The evaluation index can be a spot diagram and an optical transfer function (MTF).

[0064] In a specific embodiment, the imaging quality data of the infrared optical system with an entrance pupil diameter of 20 mm obtained by the above-mentioned achromatic method of the present application in an optical design software (such as ZEMAX optical design software) is shown in Figure 8 As shown in Figure 8 (a), the Airy disk radius is 7.91 um, the RMS spot radius is 1.54 um, the maximum spot radius is 2.99 um, and the RMS spot radius is less than one half of the Airy disk radius. Therefore, it can be seen that the infrared optical system has good image quality under the set field of view.

[0065] In addition, for the optical transfer function curve of the optical system, the MTF value is greater than 0 and less than 1, and the closer the MTF value is to 1, the better the performance of the optical system. Moreover, the closer the actual optical transfer function curve of the optical system is to the diffraction limit curve, the better the imaging quality. At the same time, since the spatial frequency (such as 10 line pairs / mm) value represents the contrast characteristic of the optical system, the higher the value, the greater the contrast of the optical system, and the higher the spatial frequency (such as 30 line pairs / mm) value, the higher the resolution of the optical system. For this reason, in Figure 8 (b), the actual optical transfer function curve of the infrared optical system is very close to the diffraction limit curve, and the normalized value is 0.91 when the spatial frequency is 10 line pairs per millimeter, and the normalized value is still higher than 0.7 when the spatial frequency is 30 line pairs / mm. Therefore, it can be seen that the infrared optical system obtained by the achromatic method of the infrared optical system of the present application has excellent contrast, resolution and other performances.

[0066] Furthermore, while keeping the shape and total optical length of the refractive lens 11 substantially unchanged, the distance d between the refractive lens 11 and the metalens 12 is adjusted. In addition, to obtain optimal focusing effect, the radius of the metalens 12 and the phase coefficient of its binary surface are adjusted accordingly, and the infrared optical system is achromatic processed using the achromatic method described above. The relationship between the distance between the refractive lens 11 and the metalens 12 and the size of the metalens is as follows:

[0067] r' = r[1 + (d - d')]

[0068] Where, r ′ d represents the adjusted radius of the metalens. ′ d represents the distance between the adjusted refractive lens 11 and the meta-lens 12, r represents the distance between the original refractive lens 11 and the meta-lens 12, and r represents the radius of the original meta-lens.

[0069] As can be seen from the above formula, in this invention, when the distance between the refractive lens and the metalens is reduced, the radius of the metalens increases. This is because the smaller the size of the metalens relative to the entire infrared optical system, the larger the infrared optical system that can be fabricated will be. Therefore, a larger distance between the refractive lens and the metalens is more conducive to the design and optimization of the entire infrared optical system, and thus makes it easier to obtain an infrared optical system with good image quality.

[0070] In a specific embodiment, such as Figures 9-10 As shown, this embodiment presents imaging quality data of an infrared optical system with an entrance pupil diameter of 20 mm obtained using the achromatic aberration method described above in this invention, within optical design software (such as ZEMAX optical design software). Wherein, Figure 9 The diagram shows the dot plot variation and optical transfer function (MTF) curve of the infrared optical system obtained by the achromatic method described above in this invention under different spacing conditions between the refracting lens and the metalens. Figure 10 It shows Figure 9 A bar chart of the various data.

[0071] Specifically, in Figures 9-10When the distance between the refractive lens and the metalens is 10 mm, the Airy disk radius of the infrared optical system obtained after achromatic processing using the above-described achromatic method of the present invention is 7.91 μm, the RMS spot radius is 1.54 μm, the maximum spot radius is 2.99 μm, and the total optical length is 19.92 μm. When the distance between the refractive lens and the metalens is 8 mm, the Airy disk radius of the infrared optical system obtained after achromatic processing using the above-described achromatic method of the present invention is 8.38 μm, the RMS spot radius is 2.07 μm, the maximum spot radius is 3.6 μm, and the total optical length is 18.91 μm. When the distance between the refractive lens and the metalens is 6 mm, the Airy disk radius of the infrared optical system obtained after achromatic processing using the above-described achromatic method of the present invention is 8.6 μm, the RMS spot radius is 4.79 μm, the maximum spot radius is 9.36 μm, and the total optical length is 18.82 μm. When the distance between the refractive lens and the metalens is 4 mm, the Airy disk radius of the infrared optical system obtained after achromatic processing using the above-described achromatic method of the present invention is 8.75 μm, the RMS spot radius is 7.25 μm, the maximum spot radius is 14.29 μm, and the total optical length is 18.75 μm. Therefore, it can be seen that when the distance between the refractive lens and the metalens of the infrared optical system gradually decreases from 10mm to 8mm, 6mm, and 4mm, the RMS spot radius and the maximum spot radius of the infrared optical system obtained after achromatic processing using the above-mentioned achromatic method of the present invention show a significant increasing trend, and the optical transfer function curve also significantly deviates from the diffraction limit. The reason for this is...

[0072] ′

[0073] The reason for this situation is as follows: Figure 11 As shown in the figure, H1 and f1 are the principal optical planes and focal length of the refracting lens, respectively, and H2 and f2 are... ′The optical main surface and focal length of the superlens respectively, f' is the focal length of the infrared optical system, U1 and U2 respectively represent the focusing ability of the refractive lens and the superlens, i.e., optical power, the height of the light ray when incident to the refractive lens and the superlens is h1 and h2 respectively, when the distance between the refractive lens and the superlens is small, because the light group focal point positions corresponding to the refractive lens and the superlens become close, the difference between the focal lengths of the two lenses will be smaller, the focusing effect of the light provided by the superlens is reduced, the chromatic aberration required to be corrected by the superlens is smaller, and then the increase of the size of the superlens reduces the compensation ability for the aberration introduced by the refractive lens, and the introduced spherical aberration is obviously larger, therefore, even if the infrared optical system is optimized by using the achromatic method of the application in the optical design software, the refractive lens and the superlens cannot reach the ideal state, and then the image quality of the corresponding infrared optical system is poor, and a good imaging effect cannot be obtained. Therefore, under the condition that the distance between the refractive lens and the superlens is large, the application is easier to obtain an infrared optical system with good image quality.

[0074] Compared with the prior art, the achromatic method of the infrared optical system of the application realizes high light transmittance and accurate phase of the superlens by inversely optimizing the parameters of the nano atoms arranged on the surface of the superlens by using the focusing efficiency of the infrared optical system, and then realizes the achromatism of the infrared optical system, so that the infrared optical system can realize good focusing imaging in the 8-12um wave band, the focusing efficiency is improved, and the imaging quality is good. At the same time, in the application, the positive dispersion effect of the refractive infrared optical lens is matched with the negative dispersion effect of the superlens, which is more conducive to realizing the achromatism of the infrared optical system. In addition, in the application, the superlens and the refractive lens are combined, compared with the traditional optical system, the number of optical elements is reduced, and the volume and weight of the optical system are reduced, which is more advantageous for the infrared optical system which has less selectable materials and higher requirements for system volume and weight. Compared with the superlens field, the application provides a new idea for the achromatism realization of the infrared optical system, and provides the possibility for the design of smaller and more complex infrared optical systems.

[0075] The above-mentioned embodiments only express several embodiments of the application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the application, a number of modifications and improvements can be made, and the application also intends to include these modifications and improvements.

Claims

1. An achromatization method for an infrared optical system, wherein, The infrared optical system comprises a refractive lens and a metasurface arranged in sequence from an object side to an image side, the metasurface comprises a substrate and a plurality of nano-atoms arranged on the surface of the substrate; characterized by comprising the following steps: S1, obtaining the phase distribution and light transmittance distribution of the nano-atoms within the size variation range of the nano-atoms, and obtaining the phase profile curve of the binary surface type of the metasurface; S2, obtaining the arrangement parameters of the nano-atoms on the metasurface according to the phase distribution and light transmittance distribution of the nano-atoms and the phase profile curve of the metasurface; S3, obtaining the parameters of the optimized infrared optical system according to the parameters of the infrared optical system and the arrangement parameters of the nano-atoms on the metasurface obtained in step S2; S4, FDTD simulation experiment, obtaining the focusing efficiency of the optimized infrared optical system; S5, when the focusing efficiency is greater than or equal to a set threshold, outputting the parameters of the optimized infrared optical system; when the focusing efficiency is less than a set threshold, returning to step S2 to adjust the arrangement parameters of the nano-atoms of the metasurface until the focusing efficiency is greater than or equal to the set threshold; After returning to step S2, the size of the nano-atoms and the interval between adjacent two nano-atoms are adjusted.

2. The achromatic method of claim 1, wherein: The nano-atoms comprise at least two of nano-ring columns, nano-cylinders and nano-square columns.

3. The achromatic method of claim 2, wherein: The inner diameter of the nano-ring column is 0.5-1 um, the outer diameter is 1.5-2 um, the radius of the nano-cylinder is 0.5-2 um, and the radius of the nano-square column is 1.5-4 um, and the height of the nano-ring column, the nano-cylinder and the nano-square column is 6 um.

4. The achromatic method of claim 3, wherein: In step S5, after returning to step S2, the adjustment of the size of the nano-atoms and the interval between adjacent two nano-atoms is specifically: setting the maximum radius of the nano-cylinder and the nano-ring column to be less than 2 um, the maximum side length of the nano-square column to be less than 4 um, and the interval between adjacent two nano-atoms to be greater than or equal to 4 um.

5. The achromatic method of claim 4, wherein: The interval between the refractive lens and the metasurface is 4-10 mm.

6. The achromatic method of claim 5, wherein: The interval between the refractive lens and the metasurface is 10 mm.

7. The achromatic method according to any one of claims 1 to 6, characterized in that: The refractive lens is a positive lens with double-sided aspheric surface, and the metasurface has a negative dispersion effect.

8. The achromatic method of claim 7, wherein: The material of the refractive lens is zinc selenide, the substrate is barium fluoride, and the nano-atoms are germanium.

9. An infrared optical system characterized by: The infrared optical system is obtained by the achromatic method of any one of claims 1-8.

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