Design evaluation method for optical system with mixed large-aperture super-structure lens and refraction lens

Abstract

The invention discloses a large-aperture super-structure lens and refraction lens mixed optical system design evaluation method, which comprises the following steps: (1) carrying out ray tracing optimization design based on a phase surface of a large-aperture super-structure lens and a refraction lens to obtain a target phase equation of the phase surface of the super-structure lens; (2) establishing a metasurface unit database forming the metasurface lens, and arranging metasurface units to fit a target phase of the large-aperture metasurface lens; (3) evaluating the phase fitting degree and the imaging quality of the optical system by using a large-aperture super-structure lens full-wave simulation substitution method, and evaluating the imaging quality of the optical system by using a ray tracing method; evaluating the image quality indexes of the super-structure lens and the hybrid optical system, and if the image quality indexes meet the technical requirements, completing the design of the folding and super hybrid optical system; and if the technical requirements are not met, returning to the step (1) to carry out design optimization. By using the method provided by the invention, the imaging quality of the super-structure lens in the hybrid system can be effectively evaluated.

Description

Technical Field

[0001] This invention belongs to the field of optical system technology, and relates to a design and evaluation method for an optical system that combines a large-aperture meta-lens with a refractive lens, and particularly to a design and evaluation method for a hybrid optical system that combines a large-aperture meta-lens with a refractive lens. Background Technology

[0002] Metalenses are a specific application of metasurfaces, using arrayed metacells to modulate the amplitude, frequency, and phase of incident light. Combining metalenses with traditional refractive lenses can overcome existing performance bottlenecks in optical systems, improve image quality, and reduce system size. Therefore, hybrid optical systems combining metalenses and refractive lenses (referred to as hybrid super-refractive systems) have promising application prospects.

[0003] Because the analytical and computational methods required for refracting lenses and metalenses differ (e.g., traditional refracting lenses use geometric optics analysis and ray tracing calculations, while metalenses use Maxwell's equations and the finite-difference time-domain method), traditional optical system design methods are difficult to apply to the design optimization and evaluation of hybrid refracting-metalenses. Metacells exist at the subwavelength scale; the metacells of typical long-wave infrared metalenses are micrometer-scale, while the aperture of metalenses in hybrid systems is typically millimeter-scale. Apertures > 1 mm can be considered large-aperture metalenses, and the number of metacells in large-aperture metalenses can reach millions. The computational load required for full-wave simulation is enormous, sometimes even requiring a supercomputer to handle the calculations. Furthermore, existing methods do not address how to evaluate the imaging quality of the metalens in the hybrid system during the design process. For example, CN117075333A discloses a design method and optical device for an optical system, calculating the focal length of the metalens based on the operating wavelength and target performance parameters to construct the initial structure of a hybrid refracting-meta-optical system; CN117687203A discloses a design method for a hybrid optical system combining a metalens and a refractive lens, using a particle swarm optimization algorithm to improve phase fitting accuracy, but requiring high computational power for large-aperture metalenses. Neither of these methods addresses how to evaluate the imaging quality of the metalens in the hybrid system during the design process.

[0004] To ensure that the imaging quality of large-aperture metalenses in hybrid systems matches the design results of ray tracing, an alternative method for full-wave simulation of large-aperture metalenses is needed. This method can easily evaluate the phase fit and imaging quality, compensate for the shortcomings of existing design methods, and accurately analyze whether the imaging quality of the hybrid system is affected by the refracting lens or the metalens. It is applicable to general hybrid optical systems combining large-aperture metalenses and refracting lenses. Summary of the Invention

[0005] The technical problem to be solved by this invention is:

[0006] Current design methods for hybrid optical systems lack imaging evaluation of metalenses in hybrid systems, and the design methods used require high computing power and have high design costs.

[0007] This invention provides a design method for a hybrid optical system combining a large-aperture metalens and a refractive lens, the design method comprising the following steps:

[0008] Step 1: Optimize the design of ray tracing based on the phase surface of the large-aperture metalens and the refracting lens to obtain the target phase equation of the metalens phase surface;

[0009] Step 2: Establish a database of meta-units that constitute the metalens, and arrange the meta-units to fit the target phase of the large-aperture metalens;

[0010] Step 3: Use the full-wave simulation method of large-aperture metalenses to evaluate the phase fit and imaging quality, and use the ray tracing method to evaluate the imaging quality of the optical system.

[0011] Proceed sequentially through steps 1-3. After completion, evaluate the image quality parameters of the meta-lens and hybrid optical system. If the image quality parameters meet the technical requirements, the design of the super-refractive hybrid optical system is complete, and the structural parameters of the optical system are obtained. If they do not meet the technical requirements, return to step 1 and repeat the steps for design optimization.

[0012] Furthermore, the aperture of the large-aperture meta-lens is greater than 5mm.

[0013] Further, step 1 includes the following steps:

[0014] Step 101: Based on the technical requirements, use the PW decomposition method (to solve the optical system based on the relationship between aberration theory and structural parameters) to design the initial structure of the optical system; or refer to existing lenses to design the initial structure of the optical system. The initial structure includes at least one metalens, the phase plane of the metalens is replaced by a diffraction phase plane, and the phase of the metalens adopts a centrally rotationally symmetric phase distribution;

[0015] The phase distribution equation of a metalens can be obtained using any of the following formulas:

[0016] ;

[0017] ;

[0018] ;

[0019] Where λ is the wavelength, a i and b i Let r be the phase coefficient variable, and r be the distance from the center of the phase plane of the metalens to any position.

[0020] Step 102: When optimizing the design using ray tracing, the phase planes of the refracting lens and the meta-lens are analyzed and calculated according to the generalized Snell's law, which is as follows:

[0021] ;

[0022] in, , Here, represents the refractive index of the incident medium and the refractive medium, respectively. , Here, θ represents the angle of incidence and the angle of refraction, λ represents the wavelength, and r represents the distance from the center of the phase plane of the metalens to any arbitrary position. Let be the phase gradient along the radial direction of the phase surface of the metalens, and be the phase gradient on the surface of the refracting lens. The right side of the equation is a constant 0.

[0023] Step 103: Based on the technical requirements and imaging quality performance parameters of the optical system, establish a comprehensive evaluation system for the optical system and construct an image quality evaluation function. The formula for the image quality evaluation function is:

[0024] ;

[0025] Among them, V i T represents the current performance parameter of the i-th type. i w represents the desired performance parameter of the i-th type. i The weight represents the difference between the current performance parameter and the expected performance parameter in the i-th case.

[0026] Step 104: Optimize the optical system in the direction that the evaluation function tends to zero to obtain the ideal phase distribution of the metalens and the structural parameters of the hybrid optical system.

[0027] Furthermore, step 2 includes the following steps:

[0028] Step 201: Use the finite-difference time-domain method to scan the structural parameters of the meta-units constituting the meta-lens to obtain the phase and transmittance under different structural parameters. The phase coverage range is at least greater than 2π, and the transmittance is at least greater than 80%.

[0029] The meta-unit phase modulation method is a polarization-insensitive and low-loss transmission phase method, and the transmission phase formula is:

[0030] ;

[0031] in, where λ is the wavelength and h is the height of the metaunit. eff The equivalent refractive index is determined by the material, shape, period, height, and size of the metaunit.

[0032] The meta-unit adopts a column structure of the same height, and its cross-section adopts a polarization-insensitive pattern structure with C4 symmetry, including circular, square, cross-shaped, annular, hollow square, regular hexagon, etc.

[0033] Step 202: Select metaunit combinations with transmittance greater than 80% and phase coverage greater than 2π, and divide them into 360 metaunits according to phase size to form a metaunit database, which includes metaunit structural parameters (period, height, size), corresponding phase values, and transmittance.

[0034] Step 203: Fold the rotationally symmetric target phase from the center to both sides in the range of 0 to 2π. At the same time, mesh the surface of the metalens with the period of the metacells in step 202. Each discrete surface mesh corresponds to a discrete target phase. Calculate the distance from each discrete phase point to the phase center and match it with the metacells in the metacell database. Arrange the metacells to fit the target phase of the metalens.

[0035] Furthermore, step 3 includes the following steps:

[0036] Step 301: Fit the target phase of the small-aperture metalens using the same metacell database and arrangement method, and adopt the same type of phase equation expression as the large-aperture metalens.

[0037] The maximum phase gradient of a small-aperture meta-lens should not be less than the maximum phase gradient of a large-aperture meta-lens, which is the maximum phase gradient limitation principle.

[0038] Step 302: Use the finite-difference time-domain method to analyze the actual fitted phase of the small-aperture metalens and evaluate the phase fitting degree of the small-aperture metalens. This is an alternative evaluation method for the phase fitting degree of the large-aperture metalens through full-wave simulation. The aperture of the small-aperture metalens is less than 0.2 mm.

[0039] Step 303: Analyze and calculate the ideal focal length of the phase plane of the small-aperture metalens using optical tracing methods; simultaneously, analyze the far-field projection of the small-aperture metalens along the Z-axis using the finite-difference time-domain method to calculate the actual focal length of the small-aperture metalens; evaluate the focal length error of the small-aperture metalens, which is an alternative evaluation method for full-wave simulation of the focal length error of large-aperture metalenses.

[0040] Step 304: Evaluate the imaging quality of the large-aperture hyperfoil hybrid system using ray tracing methods.

[0041] Based on the simulation results, the focal intensity distribution of the focal plane is extracted, and the point spread function (PSF) is obtained by normalization. The modulation transfer function (MTF) is then further extracted.

[0042] The RMS radius and various aberrations (field curvature, distortion) and chromatic aberration are evaluated based on the focal intensity distribution of the focal plane.

[0043] Furthermore, the structural parameters of the hybrid optical system include the material, thickness, aperture, number, inter-lens distance, curvature, and aspherical coefficient of the refractive lens and the metalens.

[0044] The beneficial effects of this invention are:

[0045] Compared with existing technologies, the design method of the hybrid optical system combining a large-aperture metalens and a refractive lens of this invention can efficiently, quickly, and cost-effectively complete the design optimization and simulation verification of the hybrid optical system. The full-wave simulation replacement method of the large-aperture metalens can analyze and evaluate the phase fitting degree and imaging quality of the large-aperture metalens at low cost, making up for the shortcomings of existing technologies and ensuring that its imaging quality in the hybrid system meets the design results of ray tracing. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the design method of the hybrid optical system combining a large-aperture metalens and a refractive lens according to the present invention.

[0047] Figure 2 This is a schematic diagram of the structure of a large-aperture refractive-hybrid optical system obtained by ray tracing in an embodiment of the present invention.

[0048] Figure 3 This is a schematic diagram of the structure of the metaunit in an embodiment of the present invention.

[0049] Figure 4 This is a database schematic diagram of a hyperstructure unit in an embodiment of the present invention.

[0050] Figure 5 This is a phase curve diagram of the target large-aperture metalens in an embodiment of the present invention.

[0051] Figure 6 This is a phase curve diagram of the target small-aperture metalens in an embodiment of the present invention.

[0052] Figure 7 This is a schematic diagram of the fitted phase in the full-wave simulation of the small-aperture metalens in an embodiment of the present invention.

[0053] Figure 8 This is a schematic diagram of the focal length of the far-field projection of the small-aperture metalens in an embodiment of the present invention.

[0054] Figure 9 This is a modulation transfer function diagram of a large-aperture hyperrefractive hybrid optical system in an embodiment of the present invention.

[0055] Figure 10This is a diffuse speckle diagram of a large-aperture hyperrefractive hybrid optical system in an embodiment of the present invention.

[0056] Figure 11 This is a schematic diagram of the field curvature and distortion of a large-aperture hyperrefractive hybrid optical system in an embodiment of the present invention.

[0057] Figure 12 This is a diagram showing the chromatic aberration curve of a large-aperture super-refractive hybrid optical system in an embodiment of the present invention. Detailed Implementation

[0058] The following is an illustration of an embodiment of the present invention. Figures 1-11 The technical solutions in this invention will be further explained and described.

[0059] Example 1

[0060] The first aspect of this application provides a design evaluation method for an optical system that combines a large-aperture metalens with a refractive lens, such as... Figure 1 As shown, a large-aperture metalens refers to a metalens with a light-transmitting aperture greater than 5 mm. A design method for a hybrid optical system combining a large-aperture metalens and a refractive lens includes the following steps:

[0061] Step 1: Optimize the design of ray tracing based on the phase surface of the large-aperture metalens and the refracting lens to obtain the target phase equation of the metalens phase surface;

[0062] Step 2: Establish a database of meta-units that constitute the metalens, and arrange the meta-units to fit the target phase of the large-aperture metalens;

[0063] Step 3: Use the full-wave simulation method of large-aperture metalenses to evaluate the phase fit and imaging quality, and use the ray tracing method to evaluate the imaging quality of the optical system.

[0064] Proceed sequentially through steps 1-3. After completion, evaluate the image quality parameters of the meta-lens and hybrid optical system. If the image quality parameters meet the technical requirements, the design of the super-refractive hybrid optical system is complete, and the structural parameters of the optical system are obtained. If they do not meet the technical requirements, return to step 1 and repeat the steps for design optimization.

[0065] Step 1 includes the following steps:

[0066] Step 101: Design the initial structure of the optical system according to the technical requirements using the PW decomposition method or by referring to existing lenses. The initial structure includes at least one metalens. The phase plane of the metalens is replaced by a diffraction phase plane, and the phase of the metalens adopts a central rotationally symmetric phase distribution.

[0067] The phase distribution equation of a metalens can be obtained using any of the following formulas:

[0068] ;

[0069] ;

[0070] ;

[0071] Where λ is the wavelength, a i and b i Let r be the phase coefficient variable, and r be the distance from the center of the phase plane of the metalens to any position.

[0072] Step 102: When optimizing the design using ray tracing, the phase planes of the refracting lens and the meta-lens are analyzed and calculated according to the generalized Snell's law, which is as follows:

[0073] ;

[0074] in, , Here, represents the refractive index of the incident medium and the refractive medium, respectively. , Here, θ represents the angle of incidence and the angle of refraction, λ represents the wavelength, and r represents the distance from the center of the phase plane of the metalens to any arbitrary position. Let be the phase gradient along the radial direction of the phase surface of the metalens, and be the phase gradient on the surface of the refracting lens. The right side of the equation is a constant 0.

[0075] Step 103: Based on the technical requirements and imaging quality performance parameters of the optical system, establish a comprehensive evaluation system for the optical system and construct an image quality evaluation function. The formula for the image quality evaluation function is:

[0076] ;

[0077] Where Vi represents the current performance parameter of the i-th type, Ti represents the expected performance parameter of the i-th type, and wi represents the weight corresponding to the difference between the current performance parameter and the expected performance parameter of the i-th type;

[0078] Step 104: Optimize the optical system in the direction that the evaluation function tends to zero to obtain the ideal phase distribution of the metalens and the structural parameters of the hybrid optical system.

[0079] Step 2 includes the following steps:

[0080] Step 201: Use the finite-difference time-domain method to scan the structural parameters of the meta-units constituting the meta-lens to obtain the phase and transmittance under different structural parameters. The phase coverage range is at least greater than 2π, and the transmittance is at least greater than 80%.

[0081] The meta-unit phase modulation method is a polarization-insensitive and low-loss transmission phase method, and the transmission phase formula is:

[0082] ;

[0083] in, where λ is the wavelength and h is the height of the metaunit. eff is the equivalent refractive index, which is determined by the material, shape, period, height, and size of the metaunit.

[0084] The meta-unit adopts a column structure of the same height, and its cross-section adopts a polarization-insensitive pattern structure with C4 symmetry, including circular, square, cross-shaped, annular, hollow square, regular hexagon, etc.

[0085] Step 202: Select metaunit combinations with transmittance greater than 80% and phase coverage greater than 2π, and divide them into 360 metaunits according to phase size to form a metaunit database, which includes metaunit structural parameters (period, height, size), corresponding phase values, and transmittance.

[0086] Step 203: Fold the rotationally symmetric target phase from the center to both sides in the range of 0 to 2π. At the same time, mesh the surface of the metalens with the period of the metacells in step 202. Each discrete surface mesh corresponds to a discrete target phase. Calculate the distance from each discrete phase point to the phase center and match it with the metacells in the metacell database. Arrange the metacells to fit the target phase of the metalens.

[0087] Step 3 includes the following steps:

[0088] Step 301: Fit the target phase of the small-aperture metalens using the same metacell database and arrangement method, and adopt the same type of phase equation expression as the large-aperture metalens.

[0089] The maximum phase gradient of a small-aperture meta-lens should not be less than the maximum phase gradient of a large-aperture meta-lens, which is the maximum phase gradient limitation principle.

[0090] Step 302: Use the finite-difference time-domain method to analyze the actual fitted phase of the small-aperture metalens and evaluate the phase fitting degree of the small-aperture metalens. This is an alternative evaluation method for the phase fitting degree of the large-aperture metalens through full-wave simulation. The aperture of the small-aperture metalens is less than 0.2 mm.

[0091] Step 303: Analyze and calculate the ideal focal length of the phase plane of the small-aperture metalens using optical tracing methods; simultaneously, analyze the far-field projection of the small-aperture metalens along the Z-axis using the finite-difference time-domain method to calculate the actual focal length of the small-aperture metalens; evaluate the focal length error of the small-aperture metalens, which is an alternative evaluation method for full-wave simulation of the focal length error of large-aperture metalenses.

[0092] Step 304: Evaluate the imaging quality of the large-aperture hyperfoil hybrid system using ray tracing methods.

[0093] Based on the simulation results, the focal intensity distribution of the focal plane is extracted, and the point spread function (PSF) is obtained by normalization. The modulation transfer function (MTF) is then further extracted.

[0094] The RMS radius and various aberrations (field curvature, distortion) and chromatic aberration are evaluated based on the focal intensity distribution of the focal plane.

[0095] The structural parameters of the hybrid optical system include the material, thickness, aperture, number, inter-lens distance, curvature, and aspherical coefficient of the refractive lens and the metalens.

[0096] In Example 1, an exemplary optical system design is performed, such as... Figure 2 As shown. The optical system operates in the 8μm to 12μm band, is suitable for 640×512 uncooled long-wave infrared detectors, has a pixel pitch of 12μm, an effective focal length of 13.0mm, a diagonal field of view ≥40°, an F / # ≤1.03, and a total optical length ≤20mm.

[0097] The specific design of the large-aperture super-refractive optical system is carried out in three steps according to the technical solution.

[0098] The first step involves optimizing the ray tracing design based on the phase plane of the large-aperture metalens and the refractive lens to obtain the target phase equation of the metalens's phase plane. The hybrid refractive-meta-optical system is then designed and optimized using the optical design software Zemax. Basic system parameters are set in the software: the system aperture image-side F-number is 1.0; wavelengths are 8μm, 10μm, and 12μm; field-of-view image-side heights are 0mm, 1.476mm, 2.459mm, 3.443mm, and 4.918mm; and the number and distribution of ray tracing samples are also set.

[0099] Referring to the initial structure of existing lenses, a three-element structure is selected, with the meta lens located in the second element. The phase plane of the meta lens is formulated using the following formula:

[0100] ;

[0101] Where a1 to a5 are phase coefficient variables.

[0102] Subsequently, optical tracking simulations were performed on three wavelengths and five fields of view based on the generalized Snell's law. A comprehensive evaluation system was established based on the technical requirements and imaging quality performance parameters of the optical system. The objective functions used for evaluation included: effective focal length, total system length, RMS radius of the speckle, field curvature, distortion, chromatic aberration, and MTF index. Appropriate weights were assigned to the objective functions to construct the evaluation function.

[0103] The refractive lens is chosen to be an aspherical surface, and the equation of the aspherical surface is as follows:

[0104] ;

[0105] 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.

[0106] By selecting variables including the phase coefficient of the metalens's phase plane, the materials of the metalens and refractive lenses, the surface curvature and thickness of the refractive lens, the distance between the lens groups, and the aspherical coefficient of the refractive lens, multiple optimization designs were performed to ultimately ensure that the optical system met the technical requirements. The resulting ray tracing diagram of a hybrid super-refractive system is shown below. Figure 2 As shown.

[0107] The specific parameters of the system are shown in Table 1 and Table 2.

[0108] Table 1 Structural parameters of large-aperture hyperrefractive hybrid optical systems

[0109] .

[0110] Table 2. Phase coefficients and aspherical coefficients of metasurfaces

[0111] .

[0112] The second step involves establishing a database of metaunits that constitute the metalens, arranging these metaunits to fit the target phase of the large-aperture metalens. Microstructures made of silicon are selected for both the substrate and the metaunits, using cylindrical structures of the same height. The cross-section is chosen as a C4-symmetric, polarization-insensitive circle, and the substrate is selected as a closely packed square. Figure 3 As shown, the finite-difference time-domain method was used to scan the structural parameters of the meta-elements, obtaining the phase and transmittance under different structural parameters. Finally, based on the processing technology level, combinations of meta-elements with transmittance greater than 80% and phase coverage greater than 2π were selected to construct a meta-element database, such as... Figure 4 As shown, its period p is 3.2 μm and its height h is 9.5 μm.

[0113] Fold the target phase from the center outwards to the range of 0 to 2π in step 1, as follows: Figure 5 As shown. Simultaneously, the metasurface is meshed with a period of 3.2 μm. Each discrete surface mesh corresponds to a discrete target phase. The distance from each discrete phase point to the phase center is calculated and matched with metacells in the metacell database. The metacells are arranged to fit the target phase of the metalens.

[0114] The third step involves evaluating the phase fit and imaging quality of a large-aperture metalens using full-wave simulation, and evaluating the imaging quality of the optical system using ray tracing. The target phase of a small-aperture metalens, with a aperture less than 0.2 mm, is fitted using the aforementioned metacell database and arrangement method. The phase equation expression is as follows:

[0115] ;

[0116] That is, a1 is -0.0696, and the phase equation expression is consistent with the type of large-aperture metalens; the target phase of the small-aperture metalens is folded from the center to both sides to the range of 0 to 2π.

[0117] like Figure 6 As shown, the maximum phase gradient of the small-aperture metalens is located at an edge radius of approximately 53 μm to 75 μm, with a phase change of 2π within this range, and approximately 7 metaunits are arranged. Figure 5 As shown, the maximum phase gradient of the large-aperture metalens is located between 2.8 mm and 4.2 mm in radius, varying by approximately 2π units, with about 438 metaunits arranged within this range. Meeting the maximum phase gradient constraint principle—the maximum phase gradient of the small-aperture metalens is not less than that of the large-aperture metalens—this small-aperture metalens can be used to evaluate the phase fit of the large-aperture metalens, thus ensuring the goodness of phase fit at the location of the most drastic phase change in the large-aperture metalens.

[0118] The actual fitted phase of a small-aperture metalens is analyzed using the finite-difference time-domain method, such as... Figure 7 As shown, the deviation of the fitted phase from the target phase at each wavelength is less than 1 rad, and the deviation of the fitted phase from the target phase at the center wavelength of 9.6 μm is less than 0.3 rad.

[0119] The focal length of each lens is crucial in an optical system, directly affecting the overall imaging performance and aberration correction capabilities. Therefore, full-wavelength simulated focal length is used to evaluate whether the designed metalens meets the imaging requirements of a hybrid optical system. Optical tracing methods are used to analyze and calculate the ideal focal length of the phase plane of the small-aperture metalens; simultaneously, the finite-difference time-domain method is used to analyze the far-field projection of the small-aperture metalens along the Z-axis, calculating the simulated focal length of the small-aperture metalens. Figure 8As shown in Table 3, the error between the ideal focal length and the simulated focal length of the small-aperture metalens is evaluated. Based on the error, it is determined whether the designed metalens model meets the imaging requirements of the hybrid optical system.

[0120] Table 3. Focal length error of small-aperture metalenses

[0121] .

[0122] The focal length error between the ideal focal length and the simulated focal length at each wavelength is ≤6.7%. This is an alternative evaluation method for full-wavelength simulation of focal length error of large-aperture metalenses, and the meta-unit database and arrangement method meet the design requirements.

[0123] The imaging quality of a large-aperture hybrid optical system was evaluated using ray tracing. Based on simulation results, the focal intensity distribution on the focal plane was extracted and normalized to obtain the point spread function (PSF). The modulation transfer function (MTF) was then further extracted. Given a pixel pitch of 12 μm for the uncooled infrared detector, the system cutoff frequency was determined to be 42 lp / mm. The resulting MTF curve of the hybrid optical system is shown below. Figure 9 As shown in Table 4, the MTF is greater than 0.3 at the cutoff frequency of 42 lp / mm.

[0124] Table 4 MTF of large-aperture hyperrefractive hybrid optical systems

[0125] .

[0126] The RMS radius and various aberrations (field curvature, distortion) and chromatic aberration are evaluated based on the focal intensity distribution at the focal plane. A diffusion speckle pattern of a large-aperture hybrid optical system is shown below. Figure 10 As shown, the blur spot in the central field of view is within one pixel size, while the blur spot in the off-axis field of view is approximately within two pixel sizes. Figure 11 As shown, the field curvature is controlled within the range of -0.1mm to +0.1mm. For example... Figure 3 As shown, distortion is controlled within -4.6%. Figure 12 As shown, the vertical chromatic difference is controlled within the range of the Airy spot.

[0127] According to a second aspect of this application, embodiments of the present invention also provide an optical device comprising an optical system designed according to the design method of any of the above embodiments.

[0128] Although the present invention has been described herein with reference to illustrative embodiments, the above embodiments are merely preferred embodiments of the present invention, and the implementation of the present invention is not limited to the above embodiments. It should be understood that those skilled in the art can design many other modifications and implementations, all of which fall within the protection scope of the present invention.

Claims

1. A method for evaluating a hybrid optical system design of a large-aperture meta-lens and a refractive lens, characterized by, Comprise: Step 1, the optimization design of ray tracing based on the phase surface of super lens and refractive lens, obtaining the target phase equation of the phase surface of super lens; Step 2, establishing the super unit database constituting the super lens, arranging the super unit to fit the target phase of the super lens; Step 3, using the full wave simulation of super lens instead of method to evaluate the phase fitting degree and imaging quality, using ray tracing method to evaluate the imaging quality of optical system; including: Step 301, using the same super unit database and arrangement method to fit the target phase of small aperture super lens, the phase equation expression adopts the same type as the large aperture super lens; The maximum phase gradient of small aperture super lens is not less than that of large aperture, that is, the maximum phase gradient limitation principle; Step 302, using finite difference time domain method to analyze the actual fitting phase of small aperture super lens, evaluating the phase fitting degree of small aperture super lens, which is the substitute evaluation method for full wave simulation of large aperture super lens phase fitting degree; Step 303, using optical tracing method to analyze and calculate the ideal focal length of small aperture super lens phase surface; at the same time, using finite difference time domain method to analyze the far field projection of small aperture super lens along Z axis, calculating the actual focal length of small aperture super lens; evaluating the focal length error of small aperture super lens, which is the substitute evaluation method for full wave simulation of large aperture super lens focal length error; Step 304, using ray tracing method to evaluate the imaging quality of large aperture super hybrid system; based on the simulation results, the focal point intensity distribution of focal plane is extracted, normalized to obtain point spread function PSF, and modulation transfer function MTF is further extracted; based on the focal point intensity distribution of focal plane, the RMS radius and various aberrations and chromatic aberrations are evaluated; Step 4, if the imaging quality meets the technical requirements, the design of super hybrid optical system is completed, and the structure parameters of optical system are obtained; if it does not meet the technical requirements, return to step 1 for design optimization.

2. The design evaluation method according to claim 1, characterized by, The super lens is a large aperture lens, and the clear aperture of the large aperture lens is greater than 5mm.

3. The design evaluation method according to claim 2, characterized by, The step 1 comprises: Step 101, according to the technical requirements, using PW decomposition method or referring to the initial structure of the existing lens design optical system, the initial structure contains at least one super lens, the phase surface of the super lens is replaced by the diffraction phase surface, and the phase of the super lens adopts the central rotationally symmetric phase distribution; The phase distribution equation of super lens uses any of the following formulas: ； ； ； where λ is the wavelength, a i and b i are phase coefficient variables, and r is the distance from the center of the phase plane of the superlens to any position. Step 102, when using ray tracing optimization design, the phase surface of refractive lens and super lens is analyzed and calculated according to the generalized Snell's law as follows: ； wherein, , are the refractive indices of the incident medium and the refractive medium, respectively, , are the incident angle and the refractive angle, respectively, λ is the wavelength, and r is the distance from the center of the phase surface of the superlens to any position, is the phase gradient of the phase surface of the superlens along the radial direction, the surface of the refractive lens has no phase gradient, and the right side of the equation is a constant 0; Step 103, according to the technical requirements and the performance parameters of the imaging quality of optical system, a comprehensive optical system evaluation system is established, and an image quality evaluation function is constructed, and the formula of the image quality evaluation function is: ； wherein V i represents the ith current performance parameter, T i represents the ith desired performance parameter, w i represents the weight corresponding to the difference between the ith current performance parameter and the desired performance parameter; Step 104, the optical system is optimized according to the direction of the evaluation function tending to zero, and the ideal phase distribution of the super lens and the structure parameters of the hybrid optical system are obtained.

4. The design evaluation method according to Claim 2, characterized by The step 2 comprises: Step 201, using the finite difference time domain method to scan the structure parameters of the super unit constituting the super lens, and obtaining the phase and transmittance under different structure parameters; The phase control mode of the super unit is a polarization-insensitive and low-loss transmission phase mode, and the transmission phase formula is:

5. wherein, is the wavelength, h is the height of the supercell, eff is the effective refractive index, which is determined by the material, shape, period, height, size of the supercell; The super unit adopts a column structure with the same height, and the cross section selects a polarization-insensitive pattern structure with C4 symmetry; Step 202, selecting a super unit combination with a transmittance greater than 80% and a phase coverage greater than 2pi, dividing the super unit into several groups according to the phase size, and constructing a super unit database.

6. The design evaluation method according to Claim 4, characterized by The step 2 further comprises: Step 203, folding the rotationally symmetric target phase in step 1 from the center to both sides to the range of 0-2pi, at the same time, meshing the surface of the super lens with the period of the super unit in step 202, each discrete surface grid corresponds to a discrete target phase, calculating the distance from each discrete phase point to the phase center and matching the super unit database of the super unit, and arranging the super unit to fit the target phase of the super lens.

7. The design evaluation method according to Claim 1, characterized by The small-aperture super lens has an optical aperture less than 0.2mm.

8. The design evaluation method according to Claim 4, characterized by According to the phase size, 360 super units are divided.

9. The design evaluation method according to Claim 1, characterized by, The super unit database comprises super unit structure parameters and corresponding phase values and transmittances, and the super unit structure parameters comprise period, height and size.

10. The design evaluation method according to any one of claims 1 to 8, characterized by, The structure parameters of the hybrid optical system comprise the material, thickness, aperture, number, distance between mirror groups, curvature of the refractive lens, and aspherical coefficient of the refractive lens.

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