A metasurface lens design method

Abstract

The application relates to the technical field of super-structure lens design methods, and discloses a super-structure lens design method, which comprises the following steps: according to focusing requirements, inversely designing the phase of a lens, simultaneously evaluating whether the phase has a suitable micro-element structure for matching, continuously optimizing, finally making each super-structure lens unit match the phase more in line with the focusing requirements and more in line with the phase that can be regulated by the actual micro-element structure, and thus the designed super-structure lens can have a larger aperture and a wider working waveband achromatic performance within the range of material and process limitations.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of super lens design method, in particular, to a super lens design method. BACKGROUND

[0002] Traditional optical lenses have chromatic aberration problems under wideband incident light due to the dispersion effect of device materials. The chromatic aberration caused by dispersion also adversely affects optical imaging systems, severely reducing focusing efficiency and imaging quality. At the same time, the traditional achromatic design method is to realize it by cascading multiple optical lenses with different surfaces. This method increases the volume, weight, complexity and cost of the optical system, and is not suitable for imaging fields such as nuclear industry, medicine and other fields that require high temperature resistance, radiation and light integration.

[0003] In order to provide clearer images and reduce color edges of images, researchers at home and abroad have proposed various design schemes of broadband achromatic super lenses. With the in-depth research of super surface in the field of light field regulation, super lens has attracted widespread attention. The super lens designed based on the principle of super surface is known for its flatness, thinness and the ability to efficiently control the amplitude, phase, polarization and frequency of light waves through sub-wavelength micro-element structures. It is composed of sub-wavelength micro elements and naturally does not have spherical aberration, has high control freedom and ultra-thin thickness, and is convenient for integration and miniaturization of optical devices, while having broadband achromatic focusing performance. And because of its light and thin structure, high diffraction efficiency, wide spectral range, and the use of materials such as silicon and germanium, super lens can be used in extreme environments such as high temperature and high radiation, laying a solid foundation for the research of miniaturized, high-performance imaging detection equipment suitable for nuclear facility environment.

[0004] However, most of the existing super lens design methods start from the ideal lens phase formula to calculate the phase of the super lens and design the structure of the super lens. This method is limited by the limited electromagnetic regulation ability of the micro-element structure. As the lens aperture increases, the micro-element structure cannot meet the phase regulation requirements of multiple wavelengths at the same time, so it is difficult to obtain a large-aperture, broadband, high-efficiency achromatic super lens. SUMMARY

[0005] The present application proposes a super lens design method. According to the focusing requirements, the lens phase is designed in reverse, and whether the phase has a suitable micro-element structure for matching is evaluated. Through continuous optimization, the matching phase of each super lens unit is more in line with the focusing requirements and more in line with the regulation phase that the actual micro-element structure can regulate. Therefore, the designed super lens can have larger aperture and wider working wavelength achromatic performance within the limits of materials and processes.

[0006] The technical scheme of the present application is as follows:

[0007] A superlens design method, comprising the following steps:

[0008] S100: determining suitable materials as the base and micro-element structure of the broadband achromatic superlens, and determining the lens size, focal length and working waveband;

[0009] S200: using a reverse optimization algorithm to perform reverse design on the phase arrangement of the superlens;

[0010] S300: importing the optimized phase into the micro-element structure database to obtain the actual matching phase, evaluating the focusing performance of the actual matching phase, and determining whether the design requirements are met; if the design requirements are not met, returning to S200 to re-optimize the phase; if the design requirements are met, entering S400;

[0011] S400: arranging the matched micro-elements according to the corresponding phase arrangement and performing simulation verification;

[0012] S500: completing the design through simulation verification.

[0013] Further, the working waveband determination method in step S100 is:

[0014] Determine the scanning range of the working waveband of the superlens, and select a plurality of discrete wavelengths from the continuous working waveband as the simulation calculation wavelengths based on the computer performance.

[0015] Further, the base determination method of the lens micro-element in step S100 is:

[0016] The length and width of the base of the lens micro-element are used as the period of the micro-element.

[0017] Further, the lens size determination method in step S100 is:

[0018] The size of the designed superlens is determined according to the number of micro-elements.

[0019] Further, the micro-element structure and material determination method in step S100 is:

[0020] S110: both the base and the nanometer column are selected from optical lens materials, and the optical lens materials can be silicon, titanium dioxide or quartz;

[0021] S120: the micro-element types are divided into five types: square column, cylindrical column, circular ring column, single base bearing four rectangular columns, and single base bearing four cylindrical columns; the geometric parameters of the rectangular column and the cylindrical column are the side length L and the radius R, respectively; the geometric parameters of the circular ring column are the inner diameter R1 and the outer diameter R2, and the geometric parameters of the last two are consistent with those of the single rectangular column and the single cylindrical column.

[0022] Further, the reverse optimization algorithm in step S200 includes:

[0023] S210: Optimize the lens phase surface;

[0024] S220: Fill in the optimized phase surface with the micro-element database;

[0025] S230: After filling the optimized phase surface into the micro-element structure, the super lens composed of the micro-element structure modulates the incident light field;

[0026] S240: Different wavelengths of incident light are modulated by the super lens to obtain corresponding focused light fields on the focusing plane;

[0027] S250: Calculate the loss between the actual focusing plane light field and the ideal focusing plane light field using the loss function;

[0028] S260: Return to step S210 by reverse iteration.

[0029] Further, the modulation method of step S230 includes:

[0030] The incident light field of the first wavelength passes through the super lens to obtain the output light field at the back surface of the super lens , and the modulation process formula of the phase is: ;

[0031] wherein, and respectively correspond to the output and input light field complex amplitudes under the first wavelength, is the imaginary unit;

[0032] represents the phase control of the lens on the input light field, and after calculating the loss between the actual output light field and the ideal output light field, the phase required for reverse update is updated according to the loss using the gradient descent algorithm.

[0033] Further, the loss function calculation formula in step S250 is:

[0034] ;

[0035] ;

[0036] ;

[0037] wherein, represents the calculation of the output light field corresponding to the first wavelength on the target diffraction plane after the super surface modulation the set target light field of the corresponding first wave length , square the difference between the two, and sum the values obtained at different wavelengths , represents the ideal complex amplitude distribution of the first wave length on the focal plane, defined as the ideal distribution of the incident light on the focal plane after passing through the super lens, characterized by all the energy converging in a designated area;

[0038] for evaluating the matching degree of the actual phase of the actual micro-element and the design phase, returning the corresponding loss value, and represents the optimized phase of the first wave length at the corresponding spatial position and the phase of the actual micro-element, represents the transmittance of the actual micro-element at the first wave length at the corresponding spatial position .

[0039] Further, the verification method in step S400 includes:

[0040] S410: Select achromatic super lens with working wavelength, focal length, micro-element period, height, lens size and corresponding numerical aperture, and the x-z plane light intensity distribution, focal plane light intensity distribution and two-dimensional normalized intensity distribution curve obtained after the incident light of different wavelengths passes through the designed device;

[0041] S420: Set the evaluation size of the focusing efficiency, obtain the focusing efficiency distribution graph of the super lens at different wavelengths and the focal length offset distribution graph of the super lens at each wavelength, and analyze;

[0042] S430: On the basis of the small size super lens, try to further enlarge the size of the super lens, and try to reduce the numerical aperture of the super lens to slow down the demand for micro-element regulation, and obtain the x-z plane light intensity distribution, focal plane light intensity distribution and two-dimensional normalized intensity distribution curve;

[0043] S440: After setting the evaluation size of the focusing efficiency, obtain the focusing efficiency distribution graph of the super lens at different wavelengths and the focal length offset distribution graph of the super lens at each wavelength, and analyze;

[0044] S450: Put this parameter into electromagnetic field vector analysis software, establish a complete super lens and use vector diffraction to simulate and verify, and observe the distribution of the outgoing light field.

[0045] The working principle and beneficial effects of the present application are:

[0046] The application discloses an end-to-end achromatic meta-lens reverse design method, and the achromatic meta-lens with wide waveband, high focusing efficiency and simple micro-element structure is obtained through scalar diffraction theory analysis, meta-lens theory and gradient descent algorithm analysis. The method fully utilizes the end-to-end advantages of the intermediate process of the reverse design algorithm, that is, no need to use the phase formula forward design and manual intervention adjustment, and the achromatic effect of the lens is improved by defining the metric index of the achromatic performance of the meta-lens, calculating and optimizing the lens phase and maximizing the index. Not only is the method simple and intuitive, but also the focusing effect is better than that of the traditional design method based on the phase formula. The meta-lens designed on the basis has good achromatic performance, is light and thin, has low cost, is convenient to design, can be used in extreme environments such as high temperature and high radiation, and can be used as an imaging device in a nuclear facility environment.

[0047] In order to overcome the limitations of aperture and achromatic performance caused by starting from the ideal lens phase formula and forward designing the meta-lens, the application provides an end-to-end achromatic meta-lens design method based on reverse design. According to the reverse design idea, the phase of the lens is iteratively optimized in reverse through defining the loss function and performance index, the matching degree of the micro-element structure is evaluated, and the achromatic effect of the meta-lens is improved by minimizing the loss function. According to the design requirements, the intermediate steps do not need manual intervention, the design process is greatly simplified, the phase of each micro-element position can be directly optimized according to the design target, the phase is further optimized according to the matching degree of the micro-element structure library, and finally the optimal micro-element arrangement of the meta-lens is obtained, so that the focusing efficiency of the wideband achromatic meta-lens is effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0048] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0049] Figure 1 A flowchart for optimizing and designing the meta-lens by the diffraction neural network algorithm;

[0050] Figure 2 A demonstration diagram of the actual optimization process of the achromatic meta-lens;

[0051] Figure 3 A top view of a lens with a size of 400 mu m (the number of micro-elements is 64*64);

[0052] Figure 4 x-z plane light intensity distribution, focal plane light intensity distribution and two-dimensional normalized intensity distribution curve diagrams of incident light of different wavelengths of the achromatic meta-lens with an aperture of 400 mu m after passing through the super-lens;

[0053] Figure 5 The focusing efficiency distribution diagram of the achromatic meta-lens for each wavelength when the aperture is 400 mu m;

[0054] Figure 6 The focal length offset (percentage) distribution diagram of the achromatic meta-lens for each wavelength when the aperture is 400 mu m;

[0055] Figure 7 The simulation analysis result diagram of the broadband achromatic meta-lens with an aperture of 1600 mu m (the number of micro units is 256*256);

[0056] Figure 8 The x-z plane light intensity distribution, focal plane light intensity distribution and two-dimensional normalized intensity distribution curve diagram of the incident light of different wavelengths of the achromatic meta-lens with an aperture of 1600 mu m after passing through the meta-lens;

[0057] Figure 9 The focal length offset (percentage) distribution diagram of the achromatic meta-lens for each wavelength when the aperture is 1600 mu m;

[0058] Figure 10 The top view of the lens with an aperture of 1600 mu m (the number of micro units is 256*256) (partly taken due to too many micro units). DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0060] As shown in Figures 1-9 A meta-lens design method is composed of a plurality of micro unit structures arranged in an array, the micro unit structure includes a substrate and a micro unit arranged on the substrate, and micro units of different shapes and sizes can control the phase of incident light in different ways. The optimization design method can design the phase and structure of the meta-lens end to end according to the performance requirements, so that the incident light in the target wave band is focused at the same position, achieving the effect of broadband achromatic, and the focusing performance is not sensitive to the polarization characteristics of the incident light, which can be applied to the fields of thermal imaging, medical diagnosis, etc.

[0061] A preferred embodiment of the present application is a long infrared wide band polarization insensitive achromatic meta-lens design. In the long infrared wave band, due to its longer working wave band, the size of the micro unit of the meta-lens can be designed to be in the micron level, which can reduce the difficulty of manufacturing the meta-lens.

[0062] Specifically comprising the following steps:

[0063] S100: determining suitable materials as the base and micro-element structure of the broadband achromatic superlens, and determining the lens size, focal length and working wavelength range;

[0064] The working wavelength range determination method is:

[0065] The scanning range for determining the working wavelength range of the superlens is Based on the limitation of computer performance, 7 discrete wavelengths are selected from the continuous working wavelength range as the simulation calculation wavelengths.

[0066] The base determination method of the lens micro-element is:

[0067] The length and width of the base of the lens micro-element are fixed as the period of the micro-element , and the height of the micro-element is fixed as .

[0068] The lens size determination method in step S100 is:

[0069] The size of the designed superlens is determined according to the number of micro-elements, such as or or .

[0070] Since the phase control ability of the micro-element is limited, the designed lens is too large to cause the focusing efficiency and achromatic performance to be reduced, so the appropriate size of the lens is selected to ensure good achromatic performance. In this example, the designed (aperture about 400 μm), (aperture about 1600 μm) are taken as representatives.

[0071] The micro-element structure and material determination method is:

[0072] S110: The base and nanometer column are both selected as optical lenses, and the optical lens material can be silicon, titanium dioxide or quartz, etc.

[0073] The refractive index of silicon in the long infrared wavelength range is about 3.4, which is low in cost and easy to process, and has high transmittance and phase modulation ability, which is an ideal medium material.

[0074] S120: The micro-element type is divided into five types: square column, cylindrical column, circular ring column, single base bearing four rectangular columns, and single base bearing four cylindrical columns. The geometric parameters of the rectangular column and the cylindrical column are the side length L and the radius R, respectively. The geometric parameters of the circular ring column are the inner diameter R1 and the outer diameter R2, and the latter two are consistent with the geometric parameters of the single rectangular column and the single cylindrical column.

[0075] The geometric parameters of the micro-element structure are all adjustable variables to control the phase. The micro-element structure has high rotational symmetry, so that the super lens has a polarization-independent characteristic.

[0076] S200: using a reverse optimization algorithm to perform reverse design on the phase arrangement of the super lens, each micro-element corresponding to a phase unit to be optimized Each phase unit controlled by the micro-element is regarded as an optimization object, and the focusing process is the free-space diffraction of the incident light through the super lens. After obtaining the output light field at each wavelength, the system loss value can be calculated according to the loss value.

[0077] In this embodiment, the phase control of the super lens is regarded as an optimization object, and the loss obtained by calculation is optimized. The reverse optimization algorithm includes the following steps:

[0078] S210: optimizing the phase surface of the lens

[0079] S220: filling the optimized phase surface into the micro-element database

[0080] S230: after filling the optimized phase surface into the micro-element structure, the super lens composed of the micro-element structure performs wavefront modulation on the incident light field

[0081] In order to make full use of the micro-element structure with limited types and control ability, and further improve the focusing imaging performance of the super lens by optimizing the measurement index, the present application attempts to take the incident light plane and the focusing plane as the input and output of the system respectively, and takes the phase of the super lens as an intermediate variable. The difference between the ideal output and the actual output is used to reverse optimize the intermediate variable, that is, the micro-element arrangement of the lens, so as to obtain a super lens with better focusing effect. Here, we use the gradient descent algorithm to optimize, and use the form of complex amplitude light field to represent the input and output light signals. The phase modulation method of the super lens on the light field can be expressed as:

[0082] The incident light field of the first wavelength passes through the super lens, and the output light field at the back surface of the super lens can be obtained , then the modulation process formula of the phase is: ;

[0083] wherein, and correspond to the output and input light field complex amplitudes of the first wavelength, is an imaginary unit; represents the phase control of the lens on the input light field, and when the loss between the actual output light field and the ideal output light field is calculated, the phase to be controlled is updated in the reverse direction according to the loss using the gradient descent algorithm ;

[0084] Indicates the first The ideal complex amplitude distribution of a wavelength in the focal plane is defined as the ideal distribution of incident light in the focal plane after passing through a metalens. The characteristic of this distribution is that all energy is concentrated in a specified region (the specified region is generally set to a micro-element size).

[0085] The image formed by focusing all incident light into a designated area on the focal plane after passing through the metalens is taken as the target image of the end-to-end system. If all light is focused within the designated area, the lens is considered to have achieved the target focusing effect. A loss function is established based on this, primarily including the difference between the actual image obtained after incident light passes through the metalens and the target image, as well as the matching difference between the designed micro-element structure and the optimized phase surface. After calculating the loss, the phase of the micro-element of the metalens is continuously adjusted using a gradient descent algorithm, making the actual output light field increasingly closer to the target output light field, and focusing light in the working wavelength band at the same position as much as possible. Finally, the most suitable micro-element structure is filled into the trained phase surface to achieve the achromatic function of a single-layer metalens. Compared with traditional methods, this inverse phase optimization algorithm not only simplifies the device design process as much as possible through end-to-end optimization, but also provides the optimal micro-element arrangement under the limited modulation capability of the micro-element, further improving the focusing effect of the lens and providing an effective approach for developing wide-band achromatic metalenses.

[0086] S240: Incident light of different wavelengths is modulated by a metalens to obtain a corresponding focused light field on the focusing plane;

[0087] S250: Calculate the loss between the actual focusing plane optical field and the ideal focusing plane optical field using the loss function;

[0088] The formula for calculating the loss function in step S250 is as follows:

[0089] ;

[0090] ;

[0091] The first part of the loss function The loss value is determined by the difference between the actual output light field and the ideal output light field formed by focusing all the input light into a specified area, and returns the corresponding loss value; among which, This indicates the calculation of the first [item] after metasurface modulation. The light field distribution of the emitted light corresponding to each wavelength on the target diffraction plane With the corresponding number The target light field with a set wavelength The square of the difference between them is then summed with the values ​​obtained at different wavelengths. , Indicates the first The ideal complex amplitude distribution of a wavelength in the focal plane is defined as the ideal distribution of incident light in the focal plane after passing through the metalens. This distribution is characterized by all energy converging in a specified region. When the phase is reduced, the optical field distribution on the optimized phase plane in the focal plane is closer to the target optical field distribution.

[0092] ;

[0093] This is used to evaluate the degree of matching between the actual controlled phase of the micro-element and the designed phase surface, and returns the corresponding loss value. and They represent the corresponding spatial positions. Place, No. The optimized phase at each wavelength and the phase of the actual infinitesimal elements. Indicates the corresponding spatial location At that location, the actual owner of the micro-element is at the [location missing]. The transmittance at each wavelength is calculated using an equation whose main purpose is to optimize the phase plane to closely approximate the actual tunable phase of the micro-element in the database. When As the phase is reduced until it stabilizes, the optimized phase surface closely approximates the actual phase surface obtained by the corresponding combination of metasurface micro-elements.

[0094] Through reasonable adjustment , The total loss is calculated by adding the weights of the two factors together. And use gradient descent in reverse iteration for optimization calculation. By repeatedly iterating and adjusting the phase units, the total loss value gradually decreases until convergence, and the lens focusing efficiency is improved again; setting indicators The corresponding meta-lenses, after being selected, transmit incident light of various wavelengths, resulting in different focusing efficiencies, energy levels, and other performance indicators at the focal plane. Through reasonable setting... and When the loss value decreases and these performance parameters increase, the results are saved for different wavelengths of output phase surface until no better results appear.

[0095] S260: Return to step S210 by reverse iteration.

[0096] S300: Import the optimized phase into the micro-element structure database for matching to obtain the actual matching phase. Evaluate the focusing performance of the actual matching phase to determine whether it meets the design requirements. If it does not meet the design requirements, return to S200 to re-optimize the phase. If it meets the design requirements, proceed to S400.

[0097] S400: After the matched micro-elements are arranged according to the corresponding phases, simulation verification is performed to observe the actual focusing and achromatic effect in the working waveband. In this embodiment, the most suitable micro-elements are selected from the owned micro-elements to fill in each phase unit, and a complete metasurface lens can be obtained.

[0098] The corresponding micro-elements can be selected to fill in the metasurface lens to simulate the actual situation, perform simulation verification, and observe the actual focusing and achromatic effect in the working waveband.

[0099] The metasurface lens device is manufactured according to the obtained device parameters through micro-nano manufacturing technology, and then a test optical system is built to experimentally test and research the function and performance of the metasurface lens device.

[0100] The above verification method establishes design of two metasurface lenses with different aperture sizes, which specifically includes:

[0101] S410: 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, and 12 μm are selected as the working wavelengths, the focal length is f = 800 μm, the micro-element period is , and the height is 8 μm; the lens size is 64x64 (the aperture is about 400 μm), the corresponding numerical aperture NA is 0.33, and the achromatic metasurface lens. The x-z plane light intensity distribution, focal plane light intensity distribution, and two-dimensional normalized intensity distribution curve obtained after the incident light of different wavelengths passes through the device are as shown in Figure 4 .

[0102] The focusing efficiency distribution of the metasurface lens under different wavelengths is as shown in Figure 5 , and the focal length shift (percentage) distribution of the super lens under each wavelength is as shown in Figure 6 . Through comprehensive analysis of the picture and table data, the small-size metasurface lens with an aperture of 400 μm designed in this chapter basically realizes the achromatic focusing function in the wavelength range of 9-12 μm, has high focusing efficiency, achromatic ability, and a half-peak full width close to the diffraction limit.

[0103] S420: After the focusing efficiency evaluation size is set to 7x7, the focusing efficiency distribution graph of the metasurface lens under different wavelengths and the focal length shift distribution graph of the super lens under each wavelength are obtained, and analysis is performed;

[0104] S430: On the basis of the small-size metasurface lens, the size of the metasurface lens is further expanded, and the numerical aperture of the metasurface lens is tried to be reduced to slow down the demand for micro-element regulation and control. The x-z plane light intensity distribution, focal plane light intensity distribution, and two-dimensional normalized intensity distribution curve are as shown in Figure 4 ;

[0105] Specifically, the working wavelengths 9-12 μm, and 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm are selected as working wavelengths; focal length , the micro-element period and the height are constant, and the lens size is increased to (aperture is about 1600 μm), and the corresponding numerical aperture NA is 0.16 of the achromatic superlens.

[0106] S440: the evaluation size of the focusing efficiency is set to After that, the focusing efficiency distribution of the superlens at different wavelengths is as shown in Figure 5 , and the focal length offset (percentage) distribution of the superlens at each wavelength is as shown in Figure 6 , for analysis.

[0107] According to the comprehensive analysis of the above chart data, the superlens with an aperture of 1600 μm designed in the embodiment basically realizes the achromatic focusing function in the wavelength range of 9-12 μm, has high focusing efficiency, achromatic ability, and a full width at half maximum close to the diffraction limit.

[0108] S450: put this parameter into electromagnetic field vector analysis software, establish a complete superlens, and use vector diffraction for simulation verification, and observe the distribution of the outgoing light field.

[0109] The focusing effect obtained by using the finite time domain difference method to verify the obtained superlens is basically consistent with the diffraction simulation, which not only shows that the optimization design method and program are reliable, but also has better performance than the traditional phase formula design method, and can achieve good achromatic effect. The simulation verification result is sent to processing to obtain a superlens physical device, and an optical system is built using the obtained superlens for experiment, and the experimental result shows that the actual focusing efficiency of the superlens is consistent with the simulation, and has good wide-band achromatic effect.

[0110] S500: complete the design through simulation verification.

[0111] Compared with the existing conventional superlens design technology, the present application does not use the method of calculating the phase based on the conventional lens formula calculation imaging to calculate the phase, but through the reverse design phase optimization algorithm, the performance of the superlens is judged by setting the loss function and index, and the gradient descent reverse iteration is used to maximize the index and minimize the loss function, so that the phase and micro-element arrangement of the lens are optimized. The method uses an end-to-end design idea to directly optimize the exit light field from the incident light field without artificial design feature extraction or other intermediate steps, simplifying the design process of the superlens and reducing the cost of human intervention. Moreover, because the reverse design algorithm can accurately optimize each micro-element phase according to the difference between the actual phase surface and the ideal focusing effect phase surface, and optimize the micro-element arrangement according to the difference between the actual micro-element structure and the optimized phase surface, the algorithm can further improve the focusing effect and achromatic performance of the lens compared with the traditional design method. The wide-band achromatic polarization-insensitive superlens designed on this basis not only has a simple design, but also has good effect, a relatively simple micro-element structure, easy processing and batch production, which greatly reduces the manufacturing cost of the optical system. At the same time, because it is made of materials such as silicon and germanium, it can adapt to high temperature, high radiation and other environments, so it is also suitable for imaging in nuclear facility environment, and has strong practicability.

[0112] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A metasurface lens design method, characterized in that, The method comprises the following steps: S100: determining suitable materials as the base and micro-element structure of the broadband achromatic superlens, and determining the lens size, focal length and working wavelength; S200: using a reverse optimization algorithm to perform reverse design on the phase arrangement of the superlens; S300: importing the optimized phase into the micro-element structure database to obtain the actual matching phase, evaluating the focusing performance of the actual matching phase, and determining whether the design requirements are met; if not, returning to S200 to re-optimize the phase; if yes, entering S400; S400: arranging the matched micro-elements according to the corresponding phase, and then performing simulation verification; S500: completing the design through simulation verification; The reverse optimization algorithm in step S200 comprises: S210: optimizing the lens phase surface; S220: filling the optimized phase surface with the micro-element database; S230: after the optimized phase surface is filled into the micro-element structure, the superlens composed of the micro-element structure performs wavefront modulation on the incident light field; S240: different wavelengths of incident light are modulated by the superlens to obtain corresponding focused light fields on the focusing plane; S250: using a loss function to calculate the loss between the actual focusing plane light field and the ideal focusing plane light field; S260: returning to step S210 through reverse iteration; The modulation method in step S230 comprises: The incident light field of the first wavelength is obtained The incident light field of the first wavelength is obtained The exit light field at the rear surface of the super lens is obtained The modulation process formula of the phase is ; wherein, corresponding to the output and input optical field complex amplitudes at the lth wavelength, respectively, is the imaginary unit; representing the phase control of the lens to the input light field, when the loss between the actual output light field and the ideal output light field is calculated, the required phase control is updated in reverse according to the loss using the gradient descent algorithm ; The loss function calculation formula in step S250 is: ； ； ； in, This indicates the calculation of the first [item] after metasurface modulation. The light field distribution of the emitted light corresponding to each wavelength on the target diffraction plane With the corresponding number The target light field with a set wavelength The square of the difference between them is then summed with the values ​​obtained at different wavelengths. , Indicates the first The ideal complex amplitude distribution of a wavelength in the focal plane is defined as the ideal distribution of incident light in the focal plane after passing through the metalens. The characteristic of this distribution is that all energy is concentrated in a specified region. for evaluating the matching degree between the actual phase of the actual owned micro-element and the design phase plane, returning the corresponding loss value, and respectively represent the optimized phase at the corresponding spatial position , the phase of the actual owned micro-element at the first wavelength, respectively represent the optimized phase at the corresponding spatial position , the transmittance of the actual owned micro-element at the first wavelength, respectively represent the optimized phase at the corresponding spatial position , the transmittance of the actual owned micro-element at the first wavelength, 2. The method of designing a meta-lens of claim 1, wherein, The working wavelength determination method in step S100 is: Determining the scanning range of the working wavelength of the superlens, and selecting a plurality of discrete wavelengths from the continuous working wavelength as the simulation calculation wavelength based on the computer performance.

3. The method of designing a metamaterial lens according to claim 2, wherein, The base determination method of the lens micro-element in step S100 is: Taking the length and width of the base of the lens micro-element as the period of the micro-element.

4. The method of designing a metamaterial lens according to claim 3, wherein, The lens size determination method in step S100 is: Determining the size of the designed superlens according to the number of micro-elements.

5. The method of designing a metamaterial lens according to claim 4, wherein, The micro-element structure and material determination method in step S100 is: S110: both the base and the nanometer column are selected from optical lens materials, and the optical lens materials can be silicon, titanium dioxide or quartz; S120: the micro-element types are divided into five types: square column, cylindrical column, circular ring column, single base bearing four rectangular columns and single base bearing four cylindrical columns, the geometric parameters of the rectangular column and the cylindrical column are the side length L and the radius R respectively, the geometric parameters of the circular ring column are the inner diameter R1 and the outer diameter R2, and the geometric parameters of the last two types are consistent with those of the single rectangular column and the single cylindrical column.

6. The method of designing a metamaterial lens according to claim 1 or 2 or 3 or 4 or 5, wherein, The verification method in step S400 comprises: S410: selecting an achromatic superlens with a working wavelength, a focal length, a micro-element period, a height, a lens size and a corresponding numerical aperture, and obtaining the x-z plane light intensity distribution, the focal plane light intensity distribution and the two-dimensional normalized intensity distribution curve diagram of the incident light of different wavelengths after the device; S420: setting the evaluation size of the focusing efficiency, obtaining the focusing efficiency distribution diagram of the superlens under different wavelengths and the focal length offset distribution diagram of the superlens under each wavelength, and performing analysis; S430: On the basis of the small size superlens, try to further expand the size of the superlens, and try to reduce the numerical aperture of the superlens to slow down the demand for micro-element regulation and control ability, and get the x-z plane light intensity distribution, the light intensity distribution at the focal plane and the two-dimensional normalized intensity distribution curve diagram; S440: After setting the evaluation size of the focusing efficiency, the focusing efficiency distribution diagram of the superlens at different wavelengths and the focal length offset distribution diagram of the superlens at each wavelength are obtained for analysis; S450: Put this parameter into electromagnetic field vector analysis software, establish a complete superlens and use vector diffraction to simulate and verify, and observe the distribution of the outgoing light field.

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