Optical system imaging quality evaluation method and device, electronic equipment and storage medium

Abstract

The invention discloses an optical system imaging quality evaluation method and device, electronic equipment and a storage medium. The evaluation method comprises the steps of obtaining design parameters and actual processing test data of an optical system; constructing an actual processing three-dimensional model based on the design parameters and the test data; establishing an electromagnetic simulation model based on an actually processed three-dimensional model, and simulating phases actually generated by all structural units to obtain actual phase delay of the whole metamaterial lens; simulating the whole optical system and calculating an optical performance evaluation index based on the actual phase delay of the super-structure lens; and determining the acceptability of actual processing based on the optical performance evaluation index. According to the method, the influence of the processing error of the super-structure lens on the imaging quality of the optical system can be evaluated in advance, guidance is provided for design and assembly verification links in the research and development process, and the research and development speed of the folding-super hybrid optical system is increased.

Description

Technical Field

[0001] This invention relates to a method, apparatus, electronic device, and storage medium for evaluating the imaging quality of an optical system, belonging to the field of optical technology. Background Technology

[0002] With the continuous development of micro-nano fabrication technology, metalenses, as a novel type of optical element, have gradually attracted widespread attention. A metalens is a new type of optical element that arranges micro-nano structures on a two-dimensional plane in a certain way to deflect light. Metalenses can achieve the same function as traditional refractive lenses, and therefore can replace some lenses in traditional refractive optical systems. Compared with refractive optical systems, hybrid refractive-metalense optical systems (hereinafter referred to as hybrid refractive-metalense optical systems) have the advantages of reducing system size and improving image quality, and are now gradually being applied to infrared and visible light lenses.

[0003] Metalenses are fabricated using micro / nano-fabrication techniques to form arrays of micro / nano structures on a substrate surface. However, the actual fabricated micro / nano structures inevitably deviate from the designed structures. For example, currently designed metalens structural units are mostly cylinders with the same height but different diameters, arranged in a certain way on the substrate to form the metalens. However, errors are introduced during fabrication processes such as plate making, exposure, and etching, resulting in the actual fabricated cylinders having diameters, heights, and other characteristics that do not match the design. Manufacturing deviations can alter the function of the metalens and reduce the imaging quality of the entire optical system. Currently, research analyzing the impact of metalens fabrication errors on imaging quality is still relatively scarce. Existing technologies mainly rely on experimental verification after actual assembly, lacking systematic evaluation methods to predict and analyze the specific impact of fabrication errors on the performance of optical systems.

[0004] Therefore, developing a scientific and effective method, device, electronic equipment, and storage medium for evaluating the imaging quality of optical systems is the key to solving the above-mentioned technical problems. Summary of the Invention

[0005] To address the deficiencies and shortcomings in the aforementioned background technology, this invention has made improvements and innovations, aiming to provide a scientific and effective method, device, electronic device, and storage medium for evaluating the imaging quality of optical systems. This method can pre-assess the impact of meta-lens processing errors on the imaging quality of optical systems, provide theoretical guidance for the design and assembly verification stages of the R&D process, and accelerate the development of hybrid optical systems.

[0006] To solve the above problems and achieve the above-mentioned objectives, the present invention provides an optical system imaging quality assessment method, apparatus, electronic device, and storage medium, which are implemented by adopting the following design structure and the following technical solution:

[0007] An imaging quality assessment method for an optical system includes the following steps:

[0008] S1, obtain the design parameters and actual processing and testing data of the optical system;

[0009] S2, based on design parameters and test data, constructs a three-dimensional model for actual processing;

[0010] S3, based on the actual fabrication 3D model, establish an electromagnetic simulation model, simulate the actual phase generated by all structural units, and obtain the actual phase delay of the entire metalens;

[0011] S4, based on the actual phase delay of the metalens, simulates the entire optical system and calculates the optical performance evaluation index;

[0012] S5, based on optical performance evaluation indicators, determines the acceptability of actual processing.

[0013] Preferably, in step S1, the design parameters are the basic parameters of the optical system, including the working wavelength, field of view, f-number, thickness, aperture, and shape of each refractive lens, thickness, aperture, phase expression of the metalens, as well as the lens spacing and working distance.

[0014] The design parameters also include the design parameters of the meta-lens micro / nano structure unit: the shape and size of the micro / nano structure unit, the structural material, the substrate material, the cladding material, and the phase corresponding to each micro / nano structure unit;

[0015] The actual fabrication test data was obtained by measuring the key dimensions of the actual micro / nano structure using a scanning electron microscope. The actual fabrication test data included the height, lateral dimensions, sidewall verticality, and sidewall roughness of the micro / nano structure.

[0016] In cases where there are too many types of micro / nano structural units on metalenses and it is impossible to check the structural dimensions of each one, a "sampling-interpolation" method is used to obtain size information.

[0017] Preferably, in step S2, the actual processing three-dimensional model is constructed based on actual processing test data, and the actual processing three-dimensional model includes micro-nano structures and a substrate;

[0018] Each actual fabrication 3D model is established for a single structural unit of the metalens. For each micro / nano structural unit used in the metalens, a corresponding actual fabrication 3D model is established.

[0019] Preferably, in step S3, the electromagnetic simulation model is based on the actual processed three-dimensional model, with the addition of a simulation light source and a data monitoring surface, and the background medium is determined to be air. For a meta-lens operating in a wide band, an average of 5 to 10 wavelength points are selected within the operating band range, and simulation is performed at each wavelength point.

[0020] Preferably, the simulated light source is a plane wave light source, and the wavelength is determined according to the operating wavelength of the optical system being evaluated. The simulated light source is placed at the base end of the actual 3D model being processed; the data monitoring surface is placed at the air end of the actual 3D model being processed.

[0021] Specifically, the electromagnetic field data of a plane light wave propagating from the simulated light source to the data monitoring surface is calculated using the finite-difference time-domain method; the phase corresponding to the processed structural unit is calculated based on the obtained electromagnetic field data; and the phase distribution of the entire metalens is obtained based on the calculated phase of the structural unit.

[0022] Preferably, in step S4, the obtained discrete data is first subjected to polynomial fitting, and the expression of the polynomial is:

[0023]

[0024] Where φ is the actual phase of the metalens, Ai is the polynomial coefficient, r is the radial coordinate of the metalens, the origin of the coordinate system is the center of the metalens, and m is the number of polynomial terms.

[0025] Then, the fitted polynomial is used as the actual phase expression of the metalens and substituted into the optical system for calculation;

[0026] The imaging quality of the entire optical system is calculated using ray tracing.

[0027] The direction of light refraction on the surface of the metalens is determined according to the generalized Snell's law;

[0028] The modulation transfer function is used as an indicator to calculate image quality.

[0029] Before calculating the modulation transfer function, the working distance is optimized to place the system image plane in the optimal image plane position to compensate for the image plane offset caused by the processing error of the metalens.

[0030] Preferably, in step S5, the optical performance evaluation index is the modulation transfer function (MTF), which is compared with a predetermined degradation threshold for the MTF.

[0031] If the calculated modulation transfer function is lower than the preset threshold, the actual processed meta-lens is deemed unacceptable and the optical system is unusable; otherwise, it is deemed acceptable and the optical system is usable.

[0032] Preferably, this application also provides an optical system imaging quality evaluation device, the device comprising:

[0033] The input module is used to input the design parameters and actual processing test data of the optical system. The optical system consists of a refractive lens and a meta-lens. The actual processing test data is the test data of the completed meta-lens.

[0034] The calculation module is used to process and simulate based on the design parameters and processing test data to obtain the imaging quality evaluation index of the optical system.

[0035] The output module is used to output conclusions on the acceptability of the fabricated metalens and the usability of the optical system based on the imaging quality evaluation index.

[0036] Preferably, an electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements any of the methods described above.

[0037] Preferably, a computer-readable storage medium stores a computer program thereon, which, when executed by a processor, implements the method according to any one of claims 1 to 7.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] 1. This invention can pre-assess the impact of meta-lens processing errors on the imaging quality of optical systems, providing theoretical guidance for the design and manufacturing stages of the research and development process;

[0040] 2. This invention can assess the usability of an optical system without performing overall assembly, identify potential problems in the system in advance, avoid the situation where the optical system is found to be unusable after assembly, and significantly improve the efficiency and success rate of the research and development process.

[0041] 3. This invention can accelerate the development of hybrid optical systems by verifying the processing results of meta-lenses and other refractive lenses in advance, thereby reducing unnecessary assembly and debugging steps and shortening the product development cycle.

[0042] 4. This invention helps to optimize the processing quality of metalenses. By pre-evaluating processing errors, the manufacturing process can be adjusted in a timely manner to ensure that the quality of metalenses meets the requirements, thereby improving the stability and reliability of the entire optical system.

[0043] 5. This invention can significantly save time and cost in experimental verification. Through computer simulation and theoretical analysis, it reduces the need for actual assembly and multiple experiments, improves the utilization efficiency of R&D resources, and reduces R&D costs.

[0044] 6. This invention can reduce product development risks by identifying and correcting potential problems in the optical system at an early stage, ensuring the imaging quality and functional stability of the final product, thereby reducing the risk of product failure due to design or manufacturing problems. Attached Figure Description

[0045] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0046] Figure 1 This is a flowchart of the optical system imaging quality evaluation method of the present invention;

[0047] Figure 2 This is the modulation transfer function (design value) of the entire optical system in the embodiment of the present invention.

[0048] Figure 3 This is the phase change curve (design value) of the metalens in an embodiment of the present invention.

[0049] Figure 4 This is a curve showing the phase variation with radius of a micro / nano structure unit according to an embodiment of the present invention (design value).

[0050] Figure 5 This is a three-dimensional model diagram of the actual processing of the present invention;

[0051] Figure 6 This is an electromagnetic simulation model diagram of the present invention;

[0052] Figure 7 This is the phase-radius variation curve (evaluation value) of the micro / nano structure unit of the present invention.

[0053] Figure 8 This is the phase change curve (evaluation value) of the meta-lens of the present invention;

[0054] Figure 9 This is the transfer function (evaluation value) of the optical system in an embodiment of the present invention. Detailed Implementation

[0055] To make the technical means, inventive features, objectives, and effects of this invention readily understandable, the technical solution of this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0056] As per the instruction manual Figures 1 to 9 As shown, an imaging quality assessment method for an optical system includes the following steps:

[0057] S1, obtain the design parameters and actual processing and testing data of the optical system;

[0058] S2, based on design parameters and test data, constructs a three-dimensional model for actual processing;

[0059] S3, based on the actual fabrication three-dimensional model, establish an electromagnetic simulation model, simulate the phase response of all structural units, and obtain the actual phase delay of the entire meta-lens;

[0060] S4, based on the actual phase of the metalens, simulates the entire optical system and calculates the optical performance evaluation index;

[0061] S5, based on optical performance evaluation indicators, determines the acceptability of the fabricated metalens and the usability of the optical system.

[0062] Furthermore, in step S1, the design parameters are the basic parameters of the optical system, including the working wavelength, field of view, f-number, thickness, aperture, and surface shape of each refractive lens, thickness, aperture, phase expression of the metalens, as well as the lens spacing and working distance.

[0063] The design parameters also include the design parameters of the meta-lens micro / nano structure unit: the shape and size of the micro / nano structure unit, the structural material, the substrate material, the cladding material, and the phase corresponding to each micro / nano structure unit;

[0064] The actual fabrication test data was obtained by measuring the key dimensions of the actual micro / nano structure using a scanning electron microscope. The actual fabrication test data included the height, lateral dimensions, sidewall verticality, and sidewall roughness of the micro / nano structure.

[0065] In cases where there are too many types of micro / nano structural units on metalenses and it is impossible to check the structural dimensions of each one, a "sampling-interpolation" method is used to obtain size information.

[0066] In this invention, the structural forms of the micro-nano structures include, but are not limited to, cylinders, elliptical cylinders, rectangular cylinders, and cross-shaped cylinders;

[0067] Each structural form has its own specific set of lateral dimensions, which uniquely determine its shape and geometric features:

[0068] For a cylinder, its transverse dimension includes the cylinder diameter;

[0069] For an elliptical cylinder, its lateral dimensions include the length of the major axis and the length of the minor axis.

[0070] For a rectangular column, its lateral dimension includes the length of each side of the rectangle;

[0071] For a cross-shaped column, its lateral dimension includes the lengths of each side of the cross.

[0072] Specifically, the "sampling-interpolation" method is used to obtain size information. This involves first collecting the size of some micro / nano structural units, obtaining the coupling relationship between structural sizes through fitting, and then interpolating to obtain the structural size information of the uncollected units.

[0073] Furthermore, in step S2, the actual processing three-dimensional model is constructed based on the actual processing test data, and the actual processing three-dimensional model includes micro-nano structures and substrates;

[0074] Each actual fabrication 3D model is established for a single structural unit of the metalens. For each micro / nano structural unit used in the metalens, a corresponding actual fabrication 3D model is established.

[0075] In this invention, the actual number of three-dimensional models processed is not unique; the actual number of three-dimensional models processed is not fixed, but varies depending on the type and number of micro-nano structural units used in the meta-lens design.

[0076] Furthermore, in step S3, the electromagnetic simulation model adds a simulation light source and a data monitoring surface to the actual processed three-dimensional model, and determines the background medium as air. For a meta-lens operating in a wide band, an average of 5 to 10 wavelength points are selected within the working range, and simulation is performed at each wavelength point.

[0077] In this invention, step S3 is to establish an electromagnetic simulation model based on the actual three-dimensional model, calculate the phase response of each simulation structural unit, and obtain the overall phase distribution of the meta-lens through global phase synthesis. This overall phase distribution is discrete data.

[0078] Specifically, the simulated light source is a plane wave light source, and the wavelength is determined according to the operating wavelength of the optical system being evaluated. The simulated light source is placed at the base end of the actual 3D model being processed; the data monitoring surface is placed at the air end of the actual 3D model being processed.

[0079] Specifically, the electromagnetic field data of a plane light wave propagating from the simulated light source to the data monitoring surface is calculated using the finite-difference time-domain method; the actual phase generated by the processed structural unit is calculated based on the obtained electromagnetic field data; and the phase distribution of the entire metalens is obtained based on the calculated phase of the structural unit.

[0080] Preferably, the electromagnetic simulation model includes the following specific steps:

[0081] Step 1: Obtain the actual 3D model, planar light source, and data monitoring surface; the actual 3D model contains three regions: base layer, structural layer, and air layer, where the planar light source is placed in the base layer and the data monitoring surface is placed in the structural layer;

[0082] Step 2: Use the finite-difference time-domain method (FDTD) to calculate the simulated plane wave propagating perpendicularly from the plane light source to the base surface, passing through the structural layer, to obtain the electromagnetic field distribution on the data monitoring surface;

[0083] Step 3: Calculate the actual phase of the micro / nano structure unit based on the electric field data;

[0084] Step 4: Based on the actual phase of the obtained micro / nano structural units, the actual phase distribution of the entire metalens is obtained according to the arrangement of the micro / nano structural units in the metalens; the phase distribution data is in the form of three-dimensional discrete data, including two-dimensional coordinate data and one-dimensional phase data, which correspond one-to-one; the coordinate data takes the center of the metalens as the origin.

[0085] Step 5: For metalenses operating on a single wavelength, perform Step 3 only at the corresponding wavelength; for metalenses covering multiple wavelengths, select n wavelength points on average within the operating wavelength range, perform Step 3 for each wavelength point, and obtain n sets of phase data.

[0086] Furthermore, in step S4, the obtained discrete data is first subjected to polynomial fitting, and the expression of the polynomial is:

[0087]

[0088] Where φ is the actual phase of the metalens, Ai is the polynomial coefficient, r is the radial coordinate of the metalens, the origin of the coordinate system is the center of the metalens, and m is the number of polynomial terms.

[0089] Then, the fitted polynomial is used as the actual phase expression of the metalens and substituted into the optical system for calculation;

[0090] The imaging quality of the entire optical system is calculated using ray tracing.

[0091] The direction of light refraction on the surface of the metalens is determined according to the generalized Snell's law;

[0092] The modulation transfer function is used as an indicator to calculate image quality.

[0093] Before calculating the modulation transfer function, the working distance is optimized to place the system image plane in the optimal image plane position to compensate for the image plane offset caused by the processing error of the metalens.

[0094] In this invention, 1. the fitted polynomial is used as the actual phase expression of the metalens and substituted into the optical system for calculation.

[0095] The function is to introduce the actual phase of the metalens, obtained through electromagnetic simulation calculations (using polynomial fitting), into the optical system for further calculations of optical performance. The purpose is to more accurately represent the phase characteristics of the metalens in the modeling of the optical system through the fitted phase expression, thus making the analysis of the entire optical system more realistic and precise.

[0096] 2. Calculate the imaging quality of the entire optical system using ray tracing.

[0097] Function: Using ray tracing, this function simulates the propagation of light rays in an optical system, calculating the behavior of light rays within a lens system and the final imaging effect. Purpose: Ray tracing is a commonly used method for analyzing optical systems. It can accurately predict information such as image quality, distortion, and focal position, helping to evaluate whether a lens design meets the expected imaging requirements.

[0098] 3. Determine the direction of light refraction on the surface of the metalens using the generalized Snell's law.

[0099] Function: Calculates the propagation direction of incident light rays when refracted at the surface of a metalens, based on the generalized Snell's law. Purpose: The generalized Snell's law takes into account the special material properties and geometry of metalenses, accurately describing the refraction or deflection of light rays at the metalens surface, thus affecting the accuracy of image quality evaluation metrics.

[0100] 4. The modulation transfer function (MTF) is used as an indicator to calculate image quality.

[0101] Function: To evaluate the imaging quality of an optical system by calculating the Modulation Transfer Function (MTF). Purpose: MTF is a key indicator of the imaging quality of an optical system, reflecting how the system transmits information at different spatial frequencies. By calculating the MTF, the system's imaging performance, such as resolution and contrast, can be assessed, helping to identify potential imaging problems (such as blurring and distortion).

[0102] 5. Optimize the working distance before calculating the modulation transfer function to ensure the system image plane is in the optimal position, thus compensating for image plane offset caused by manufacturing errors of the metalens.

[0103] Function: Before calculating MTF, the working distance of the optical system is optimized to ensure the image plane is in the optimal position, thereby eliminating image plane offset caused by metalens manufacturing errors. Purpose: Manufacturing errors in the metalens can cause image plane position offsets, which affect image quality. By optimizing the working distance, the image plane position of the system can be adjusted, ensuring that the calculated image quality indicators are more accurate.

[0104] The working distance refers to the distance between the center of the last surface of the last glass element of the lens and the surface of the detector. The purpose of optimizing the working distance is to make the calculated imaging quality evaluation index more accurate, not to optimize the optical system.

[0105] In summary, these steps constitute a complete process for analyzing the optical performance of metalenses. The function of each step revolves around accurately calculating image quality, from the actual phase expression obtained by polynomial fitting, to evaluating image quality through ray tracing and modulation transfer function, and then to optimizing image plane position to compensate for errors. All of these can effectively improve the accuracy of image quality evaluation.

[0106] In this invention, step 4, based on the actual phase of the metalens, the simulation process of the entire optical system includes multiple steps such as the introduction of phase data, simulation of ray tracing, calculation of deflection direction, optimization of image plane MTF to evaluation of MTF; the role of each step is to ensure that the final optical performance evaluation is accurate and reliable, and the ultimate goal is to accurately evaluate the imaging effect of metalens design and its application.

[0107] Furthermore, the specific steps for calculating the imaging quality of the entire optical system using ray tracing are as follows:

[0108] 1. Calculate the pupil function. First, calculate the position of the exit pupil of the entire system. Using the ideal image point with zero field of view as the center, construct a sphere tangent to the plane of the exit pupil as a reference sphere. Traverse the zero field of view ray to the image plane position, and then trace it backward from the image plane position back to the exit pupil position. Calculate the pupil function at the exit pupil based on the tracing data. :

[0109]

[0110] in, It is the amplitude. It refers to the phase. The phase is calculated based on the optical path difference of the light ray relative to the reference sphere.

[0111] 2. Calculate the point spread function. Calculate the complex amplitude distribution on the image plane based on the pupil function. :

[0112]

[0113] in, Indicates Fourier transform, These are the coordinates on the image plane.

[0114] Complex amplitude distribution Taking the square of the modulus yields the point spread function. :

[0115]

[0116] 3. Calculate the modulation transfer function. Perform a Fourier transform on the point spread function and take the modulus to obtain the modulation transfer function.

[0117]

[0118] in, For spatial frequency, take The MTF value on the positive half-axis is used as the final optical performance evaluation index.

[0119] Optimizing the working distance: The evaluation function during optimization is the MTF value at the target spatial frequency. The ultimate goal of optimization is to find the working distance that maximizes the MTF value at the target spatial frequency.

[0120] Furthermore, in step S5, the optical performance evaluation index is the modulation transfer function (MTF), which is compared with a predetermined degradation threshold for the MTF.

[0121] If the calculated modulation transfer function is lower than the preset threshold, the actual processed meta-lens is deemed unacceptable and the optical system is unusable; otherwise, it is deemed acceptable and the optical system is usable.

[0122] The present invention also proposes an imaging quality evaluation device for an optical system, the device comprising:

[0123] The input module is used to input the design parameters and actual processing test data of the optical system. The optical system consists of a refractive lens and a meta-lens. The actual processing test data is the test data of the completed meta-lens.

[0124] The calculation module is used to process and simulate based on the design parameters and processing test data to obtain the imaging quality evaluation index of the optical system.

[0125] The output module is used to output conclusions on the acceptability of the fabricated metalens and the usability of the optical system based on the imaging quality evaluation index.

[0126] In this invention, the calculation module can also be used to compare the modulation transfer function with a predetermined degradation threshold of the modulation transfer function to determine whether it is usable, and finally output the usability conclusion through the output module.

[0127] The present invention also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method described thereon.

[0128] The present invention also proposes a computer-readable storage medium having a computer program stored thereon, the computer program being executed by a processor to describe the method.

[0129] The present invention will be further illustrated below through embodiments:

[0130] This is a long-wave infrared hybrid lens with a focal length of 13mm, compatible with a 640×512 detector, operating in the 8μm-14μm wavelength range. It comprises three lenses: the first and third lenses are refractive lenses made of chalcogenide glass, with aspherical surfaces for light transmission. The second lens is a metalens made of silicon, with a planar front surface and a metasurface rear surface. The expression for aspherical surfaces uses even-order aspherical surfaces, and the relationship for even-order aspherical surfaces is shown below:

[0131]

[0132] Where Z is the arc height along the optical axis, with the vertex of the sphere as the origin of the coordinate system; ρ is the vertex curvature, ρ=1 / r, where r is the radius; k is a quadratic constant; y is the distance between the coordinate point and the vertex of the lens sphere; A, B, C, and D are the aspherical coefficients of the corresponding orders.

[0133] The phase plane of the meta-lens is defined by the following formula:

[0134]

[0135] Where a1 to a5 are phase coefficient variables, and λ0 is the center wavelength.

[0136] The lens parameters are listed below:

[0137] surface Surface type Radius (mm) Thickness (mm) Material S1 surface unlimited unlimited － S2 aspherical 9.531 3.7 Chalcogenide Glass S3 aspherical 8.586 3.4 － S4 spherical aperture (aperture) unlimited 0.5 Silicon S5 Metasurface unlimited 1.2 － S6 aspherical -273.121 4 Chalcogenide Glass S7 aspherical -20.717 8.5 － S8 Image unlimited — －

[0138] Table 1 Structural parameters of large-aperture hyperrefractive hybrid optical systems

[0139] Surface serial number Surface type Phase coefficient or aspherical coefficient S2 aspherical k=0A=3.2817482997150000E-005B=1.6562065742920000E-006C=-1.471856176881000E-007D=3.999389216655000E-009 S3 aspherical k=-4.023454357150390E-001A=4.0709322105190000E-004B=-1.4711945 88846000E-005C=8.7012257746910000E-007D=-3.193684089866000E-008 S4 Metasurface a1=-1.077445317852000E+00a2=3.379524955088000E-002a3=-8.142086 81566500E-004a4=6.489206815152001E-005a5=-2.68121465458500E-006 S6 aspherical k=0A=-5.390172967552000E-004B=5.1791314071110000E-005C=-5.442892527024000E-006D=2.390815470487000E-007 S7 aspherical k=0A=-1.145790943142000E-004B=-8.870073798747000E-006C=3.1752154848200000E-007D=-1.018540560847000E-008

[0140] Table 2. Phase coefficients and aspherical coefficients of metasurfaces

[0141] As attached Figure 2 The calculated modulation transfer function of the entire optical system is shown; the transfer function is 0.41 at 42 lp / mm, which is close to the diffraction limit.

[0142] As attached Figure 3 The figure shows the phase change curve of the designed metalens; the horizontal axis is the radial distance from the center of the metalens; the phase change exceeds 4π rad.

[0143] The metaatoms used in the metalens are all cylindrical, with a height of 10 μm, a period of 3.5 μm, and a gradually changing diameter. (See attached image.) Figure 4 The relationship between phase and cylinder radius was demonstrated. Electron microscopy was used to examine the actual machined metalens, and the following cylinder diameters were measured: 2.36 μm, 2.58 μm, 2.76 μm, 2.92 μm, 3.05 μm, and 3.17 μm. These correspond to the design values ​​of 2.04 μm, 2.30 μm, 2.52 μm, 2.71 μm, 2.86 μm, and 3 μm. Based on these two sets of data, a polynomial fitting was used to obtain the relationship between the design diameter and the actual machined diameter, as shown in the following equation:

[0144]

[0145] in, This is the actual machining diameter value. For the design diameter value;

[0146] Different groove widths between cylinders lead to different etching depths due to etching hysteresis effects. Based on electron microscopy images, the etching depths corresponding to cylinders with diameters of 2.36 μm, 2.58 μm, 2.76 μm, 2.92 μm, 3.05 μm, and 3.17 μm are determined to be 10.05 μm, 9.90 μm, 9.71 μm, 9.40 μm, 9.04 μm, and 8.50 μm, respectively.

[0147] Based on the above etching depth and diameter data, using polynomial fitting, the relationship between etching depth and actual machining diameter can be obtained as follows:

[0148]

[0149] Where H is the etching depth and D is the cylinder diameter.

[0150] Since the working wavelength is long-wave infrared, and the difference between the maximum and minimum values ​​of the sidewall undulations measured by electron microscopy is 20 nm, which is much lower than the working wavelength, the sidewalls are set to smooth when constructing the actual processing 3D model.

[0151] A three-dimensional model of the actual processing is established based on the fitted relationship, as shown in the attached figure. Figure 5 This demonstrates one of the actual 3D models of the fabrication process, which includes the structure and the substrate.

[0152] An electromagnetic simulation model was established based on the actual processing model, as shown in the attached figure. Figure 6 The diagram shows the established electromagnetic simulation model. The phase generated by the actual fabricated micro / nano structure units was obtained through simulation at wavelengths of 8μm, 9μm, 10μm, 11μm, and 12μm. The phase difference at different wavelengths was less than 0.78 rad. Here, the phase at 10μm is used to represent the phase across the entire working wavelength range. The phase generated at 10μm is shown in the attached diagram. Figure 7 As shown. Due to the large etching error in the radius, the simulated phase difference between the fabricated and designed micro / nano structure units exceeds 3.2 rad.

[0153] In this embodiment, the metalens exhibits rotational symmetry. Based on the arrangement of the metalens during design, the actual phase discrete data of the metalens in a certain radial direction is obtained, and a curve is plotted as follows. Figure 8 As shown, the fitting is performed according to step three. The coefficient of the fitting formula is set to 20. The coefficients in the phase relationship formula of the superlens are shown below. The coefficient A0 can be ignored when calculating the optical system and will not be given here.

[0154] coefficient value A1 -3.323996357E+00 A2 2.623735828E+01 A3 -1.004014604E+02 A4 2.005853331E+02 A5 -2.406035569E+02 A6 1.889867535E+02 A7 -1.029656432E+02 A8 4.049554626E+01 A9 -1.182546478E+01 A10 2.615278053E+00 A11 -4.438579038E-01 A12 5.824890968E-02 A13 -5.924125523E-03 A14 4.653500173E-04 A15 -2.794908691E-05 A16 1.259154583E-06 A17 -4.117057344E-08 A18 9.222158980E-10 A19 -1.265537176E-11 A20 8.022053836E-14

[0155] Table 3 Phase Relationships of Metalenses

[0156] The above coefficients are used to replace the original binary phase coefficients of the metalens, and the working distance is optimized to position the system image plane at the optimal image plane. Then, the modulation transfer function of the system is calculated, such as... Figure 9 The calculated modulation transfer function is shown.

[0157] Finally, the acceptability of the actually fabricated metalens and the usability of the optical system were determined. The degradation threshold of the modulation transfer function was set as follows: the MTF of the axial transfer function at 42 lp / mm is greater than 0.25. According to the calculated modulation transfer function graph, the value of the axial transfer function at 42 lp / mm is 0.269, which is not lower than the degradation threshold. Therefore, the actually fabricated metalens is deemed acceptable and the optical system is usable.

[0158] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for evaluating the imaging quality of an optical system, characterized in that: It includes the following steps: S1, obtain the design parameters and actual processing and testing data of the optical system; S2, based on design parameters and test data, constructs a three-dimensional model for actual processing; S3, based on the actual fabrication 3D model, establish an electromagnetic simulation model, simulate the actual phase generated by all structural units, and obtain the actual phase delay of the entire metalens; S4, based on the actual phase delay of the metalens, simulates the entire optical system and calculates the optical performance evaluation index; S5, based on optical performance evaluation indicators, determines the acceptability of actual processing.

2. The method for evaluating the imaging quality of an optical system according to claim 1, characterized in that: In step S1, the design parameters are the basic parameters of the optical system, including the working wavelength, field of view, f-number, thickness, aperture, and shape of each refractive lens, thickness, aperture, phase expression of the metalens, as well as the lens spacing and working distance. The design parameters also include the design parameters of the meta-lens micro / nano structure unit: the shape and size of the micro / nano structure unit, the structural material, the substrate material, the cladding material, and the phase corresponding to each micro / nano structure unit; The actual fabrication test data was obtained by measuring the key dimensions of the actual micro / nano structure using a scanning electron microscope. The actual fabrication test data included the height, lateral dimensions, sidewall verticality, and sidewall roughness of the micro / nano structure. In cases where there are too many types of micro / nano structural units on metalenses and it is impossible to check the structural dimensions of each one, a "sampling-interpolation" method is used to obtain size information.

3. The method for evaluating the imaging quality of an optical system according to claim 1, characterized in that: In step S2, the actual processing three-dimensional model is constructed based on the actual processing test data. The actual processing three-dimensional model includes micro-nano structures and a substrate. Each actual fabrication 3D model is established for a single structural unit of the metalens. For each micro / nano structural unit used in the metalens, a corresponding actual fabrication 3D model is established.

4. The method for evaluating the imaging quality of an optical system according to claim 1, characterized in that: In step S3, the electromagnetic simulation model adds a simulation light source and a data monitoring surface to the actual processed three-dimensional model, and determines the background medium as air. For a meta-lens operating in a wide band, an average of 5 to 10 wavelength points are selected within the operating band range, and simulation is performed at each wavelength point.

5. The method for evaluating the imaging quality of an optical system according to claim 4, characterized in that: The simulated light source is a plane wave light source, and its wavelength is determined according to the operating wavelength of the optical system being evaluated. The simulated light source is placed at the base end of the actual 3D model being processed; the data monitoring surface is placed at the air end of the actual 3D model being processed. Specifically, the electromagnetic field data of a plane light wave propagating from the simulated light source to the data monitoring surface is calculated using the finite-difference time-domain method; the phase corresponding to the processed structural unit is calculated based on the obtained electromagnetic field data; and the phase distribution of the entire metalens is obtained based on the calculated phase of the structural unit.

6. The method for evaluating the imaging quality of an optical system according to claim 1, characterized in that: In step S4, the obtained discrete data is first subjected to polynomial fitting, and the expression of the polynomial is: ； Where φ is the actual phase of the metalens, Ai is the polynomial coefficient, r is the radial coordinate of the metalens, the origin of the coordinate system is the center of the metalens, and m is the number of polynomial terms. Then, the fitted polynomial is used as the actual phase expression of the metalens and substituted into the optical system for calculation; The imaging quality of the entire optical system is calculated using ray tracing. The direction of light refraction on the surface of the metalens is determined according to the generalized Snell's law; The modulation transfer function is used as an indicator to calculate image quality. Before calculating the modulation transfer function, the working distance is optimized to place the system image plane in the optimal image plane position to compensate for the image plane offset caused by the processing error of the metalens.

7. The method for evaluating the imaging quality of an optical system according to claim 1, characterized in that: In step S5, the optical performance evaluation index is the modulation transfer function (MTF), which is compared with a predetermined degradation threshold for the MTF. If the calculated modulation transfer function is lower than the preset threshold, the actual processed meta-lens is deemed unacceptable and the optical system is unusable; otherwise, it is deemed acceptable and the optical system is usable.

8. An imaging quality evaluation device for an optical system, characterized in that: The device includes: The input module is used to input the design parameters and actual processing test data of the optical system. The optical system consists of a refractive lens and a meta-lens. The actual processing test data is the test data of the completed meta-lens. The calculation module is used to process and simulate based on the design parameters and processing test data to obtain the imaging quality evaluation index of the optical system. The output module is used to output conclusions on the acceptability of the fabricated metalens and the usability of the optical system based on the imaging quality evaluation index.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, it implements the method of any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method described in any one of claims 1 to 7.

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