Titanium dioxide super-lens large-view-field achromatic imaging method and device

Abstract

The invention discloses a titanium dioxide super-lens large-view-field achromatic imaging method and device, and the method comprises the steps: building a simulation model through a time domain finite difference method, and obtaining the phase amplitude corresponding relation of TiO2 nano-column units under different sizes; and according to a first target function preset by single-wavelength super-diffraction focusing, reversely designing and iteratively optimizing the surface phase of the TiO2 super-lens by using a genetic algorithm to obtain the single-wavelength super-diffraction super-lens. And then, optimizing the genetic algorithm, and reversely designing and optimizing the phase of the single-wavelength super-diffraction super-lens again in combination with a Rayleigh-Sommerfeld diffraction formula and a second target function preset by broadband achromatism to obtain the broadband achromatism super-diffraction super-lens. And finally, point spread functions with different off-axis degrees are optimized by means of an exhaustion algorithm and an angular spectrum theory, and large-view-field achromatic super-diffraction imaging is realized. The invention effectively solves the problems of large aberration, obvious chromatic aberration, limited resolution, difficulty in parameter regulation and control and poor off-axis imaging performance of the traditional optical lens and the existing super lens in large-view-field imaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of large-field achromatic imaging of superlenses, and particularly relates to a method and device for large-field achromatic imaging of a titanium dioxide superlens. Background Art

[0002] In the field of modern optical imaging, with the continuous improvement of the requirements for imaging quality and functions, traditional optical lenses gradually expose limitations in aspects such as large field of view, achromatism, and super-diffraction imaging.

[0003] It is difficult for traditional optical lenses to simultaneously achieve large-field and high-resolution imaging. When performing large-field imaging, the aberration problem is relatively prominent. Especially in the edge field-of-view region, obvious image distortion, blurring, etc. will occur, seriously affecting the imaging quality. Moreover, traditional lenses have a chromatic aberration problem. Lights of different wavelengths have different refractive indices in the lens, resulting in differences in the focal position and imaging size, making the imaging color reproduction inaccurate and difficult to meet the high-precision requirements in multi-color light imaging applications (such as color photography, spectral analysis, etc.).

[0004] In addition, limited by the optical diffraction limit, traditional optical lenses cannot resolve details smaller than half a wavelength scale, greatly restricting their applications in the field of microscopic imaging (such as biological cell observation, nanomaterial characterization, etc.).

[0005] As a new type of optical element, a superlens is composed of sub-wavelength-scale nanostructure units and can flexibly control the characteristics of light such as phase, amplitude, and polarization, providing a new way to solve the above problems. However, at present, superlenses still face many challenges in large-field achromatic super-diffraction imaging. On the one hand, it is difficult to design and fabricate superlenses with both large field of view, achromatism, and super-diffraction capabilities, and parameters such as the size, shape, and arrangement of nanostructure units need to be precisely controlled; on the other hand, the imaging performance optimization of existing superlenses at different off-axis degrees is not perfect enough, and it is difficult to achieve uniform high-quality imaging within a large field of view. Summary of the Invention

[0006] Therefore, the present invention provides a method and device for large-field achromatic imaging of a titanium dioxide superlens to solve the problems of large aberration in large-field imaging of traditional optical lenses, chromatic aberration, and difficulty in high-resolution due to the diffraction limit, as well as the problems of difficult parameter regulation and poor off-axis imaging performance of existing superlenses in large-field achromatic super-diffraction imaging.

[0007] To achieve the above object, the present invention provides the following technical solution: A method for large-field achromatic imaging of a titanium dioxide superlens, comprising:

[0008] Constructing a simulation model of superlens nanocylinder units according to the finite-difference time-domain method to obtain the phase-amplitude correspondence of TiO2 nanocylinder units at different sizes;

[0009] According to the preset first objective function for single-wavelength super-diffraction focusing, the genetic algorithm is used to inversely design the surface phase distribution of the TiO2 superlens, and through iterative optimization, a TiO2 superlens with single-wavelength super-diffraction is obtained;

[0010] Based on the inverse design strategy of the TiO2 superlens with single-wavelength super-diffraction, the genetic algorithm is optimized. Combining the optimized genetic algorithm with the Rayleigh-Sommerfeld diffraction formula, according to the broadband achromatic aberration preset second objective function, the surface phase distribution of the TiO2 superlens with single-wavelength super-diffraction is inversely designed and iteratively optimized again to obtain a TiO2 superlens with broadband achromatic aberration super-diffraction;

[0011] Through the phase distribution of the TiO2 superlens with broadband achromatic aberration super-diffraction, using the exhaustive algorithm combined with the angular spectrum theory, the point spread functions with different off-axis degrees are optimized to achieve achromatic aberration super-diffraction imaging within a large field of view.

[0012] As an optimized scheme for the large-field-of-view achromatic imaging method of the titanium dioxide superlens, the process of obtaining the phase-amplitude correspondence relationship of TiO2 nanocolumn units with different sizes:

[0013] According to the constructed simulation model of the TiO nanocolumn unit, simulation screening is carried out to obtain the phase-amplitude modulation amount of the nanocolumn at the set wavelength; based on the correspondence relationship between the nanocolumn unit and the phase modulation amount, a wavelength-size-phase database of the nanocolumn unit is constructed;

[0014] Based on the wavelength-size-phase database, the genetic algorithm and the exhaustive algorithm are used to iteratively optimize the surface phase of the lens to obtain the required phase distribution; then according to the required phase distribution, the required size distribution of the nanocolumn unit is determined.

[0015] As an optimized scheme for the large-field-of-view achromatic imaging method of the titanium dioxide superlens, in the process of obtaining a TiO2 superlens with single-wavelength super-diffraction, the genetic algorithm is combined with the Rayleigh-Sommerfeld diffraction formula to iteratively optimize the optical response of the surface phase of the TiO2 superlens. When the surface phase of the TiO2 superlens satisfies the convergence condition that it does not change after several consecutive iterations, the iterative optimization is stopped;

[0016] In the process of obtaining a TiO2 superlens with broadband achromatic aberration super-diffraction, the surface phase of the TiO2 superlens is iteratively optimized and stopped when the same convergence condition is satisfied.

[0017] As an optimized scheme for the large-field-of-view achromatic imaging method of the titanium dioxide superlens, the expression of the first objective function preset according to single-wavelength super-diffraction focusing is:

[0018]

[0019] In the formula, is the central light field intensity at the target focal length; R = [R1, R2, …, R n is the set of nano-unit radii; n is the number of nano-units; R i is the radius of the i-th nanorod; R min and R max are the value ranges of the nanorod radii; In, p is the spacing between adjacent nanorods in the specified direction, and are the coordinates of the corresponding nanorod in the specified direction.

[0020] As an optimal solution for the large-field achromatic imaging method of the titanium dioxide superlens, the expression of the second objective function preset according to broadband achromatism is:

[0021]

[0022] In the formula, is the central light intensity at the target focal length; is the phase distribution to be optimized; FWHM(λ i ) is the full width at half maximum at the corresponding wavelength, NA is the numerical aperture; I f (λ i , r0) is the sidelobe light intensity in the field of view, is the central light intensity; r0 is the defined sidelobe range in the field of view, r FWHM and r max are the lower and upper limits of the sidelobe range, respectively.

[0023] As an optimal solution for the large-field achromatic imaging method of the titanium dioxide superlens, during the optimization process of the point spread function with different off-axis degrees by using the exhaustive algorithm combined with the angular spectrum theory, the focusing characteristics of the superlens at different off-axis degrees are calculated by using the angular spectrum theory,

[0024] The expression for calculating the focusing characteristics of the superlens at different off-axis degrees by using the angular spectrum theory is:

[0025]

[0026] Among them, I(x off , y off ; x, y) is the light intensity distribution of the off-axis point (x off , y off ) at (x, y); A(f x , f y ) is the angular spectrum of the light field near the exit surface of the superlens, which is calculated by the following formula:

[0027]

[0028] In the formula, f x , f y , f z are the frequency components along the x, y, and z directions respectively; U(x, y) represents the spherical wavefront of the off-axis point, and u0 is the initial light intensity amplitude; l r is the distance between the off-axis point (x off , y off ) in the object plane and the point (x, y) on the lens; t(r) is the transmission function of the metasurface, is the circular domain function, and φ SOM is the phase modulation amount of the metasurface; F[·] represents the Fourier transform.

[0029] The present invention also provides a titanium dioxide superlens large field of view achromatic imaging device, which adopts the above-mentioned titanium dioxide superlens large field of view achromatic imaging method, and includes:

[0030] A phase optimization and size mapping module, which is used to construct a simulation model of the superlens nanocolumn unit according to the finite-difference time-domain method, and obtain the phase-amplitude correspondence relationship of the TiO2 nanocolumn unit under different sizes;

[0031] A single-wavelength super-diffraction TiO2 superlens acquisition module, which is used to perform inverse design on the surface phase distribution of the TiO2 superlens according to the single-wavelength super-diffraction focusing preset first objective function by using the genetic algorithm, and obtain the single-wavelength super-diffraction TiO2 superlens through iterative optimization;

[0032] A broadband achromatic super-diffraction TiO2 superlens acquisition module, which is used to optimize the genetic algorithm based on the inverse design strategy of the single-wavelength super-diffraction TiO2 superlens, combine the optimized genetic algorithm with the Rayleigh-Sommerfeld diffraction formula, and perform inverse design and iterative optimization on the surface phase distribution of the single-wavelength super-diffraction TiO2 superlens again according to the broadband achromatic preset second objective function to obtain the broadband achromatic super-diffraction TiO2 superlens;

[0033] A large field of view off-axis aberration correction module, which is used to optimize the point spread function of different off-axis degrees through the phase distribution of the broadband achromatic super-diffraction TiO2 superlens by using the exhaustive algorithm combined with the angular spectrum theory, so as to achieve achromatic super-diffraction imaging within a large field of view.

[0034] As a preferred solution of the titanium dioxide superlens large field of view achromatic imaging device, the phase optimization and size mapping module includes:

[0035] The wavelength-size-phase database construction sub-module is used to perform simulation screening based on the constructed TiO nano-column unit simulation model to obtain the phase amplitude modulation amount of the nano-columns at a set wavelength; according to the correspondence between the nano-column unit and the phase modulation amount, construct a wavelength-size-phase database of the nano-column unit;

[0036] The nano-column unit size distribution determination sub-module is used to iteratively optimize the phase of the lens surface based on the wavelength-size-phase database by using the genetic algorithm and the exhaustive algorithm to obtain the required phase distribution; and then determine the required nano-column unit size distribution according to the required phase distribution.

[0037] As a preferred solution of the large field of view achromatic imaging device of the titanium dioxide superlens, in the single-wavelength super-diffraction TiO2 superlens acquisition module, the optical response of the phase of the TiO2 superlens surface is iteratively optimized by combining the genetic algorithm with the Rayleigh-Sommerfeld diffraction formula. When the phase of the TiO2 superlens surface satisfies the convergence condition that it does not change after several consecutive iterations, stop the iterative optimization;

[0038] In the broadband achromatic super-diffraction TiO2 superlens acquisition module, during the process of obtaining the broadband achromatic super-diffraction TiO2 superlens, the phase of the TiO2 superlens surface is iteratively optimized and stopped when the same convergence condition is met.

[0039] As a preferred solution of the large field of view achromatic imaging device of the titanium dioxide superlens, in the single-wavelength super-diffraction TiO2 superlens acquisition module, the expression of the first objective function preset according to the single-wavelength super-diffraction focusing is:

[0040]

[0041] In the formula, is the central light field intensity at the target focal length; R = [R1, R2,..., R n is the set of nano-unit radii; n is the number of nano-units; R i is the radius of the i-th nano-column; R min and R max are the value ranges of the nano-column radii; where p is the spacing between adjacent nano-columns in the specified direction, and are the coordinates of the corresponding nano-column in the specified direction.

[0042] As a preferred solution of the large field of view achromatic imaging device of the titanium dioxide superlens, in the broadband achromatic super-diffraction TiO2 superlens acquisition module, the expression of the second objective function preset according to the broadband achromatic is:

[0043]

[0044] In the formula, is the central light intensity at the target focal length; is the phase distribution to be optimized; FWHM(λ i ) is the full width at half maximum at the corresponding wavelength, and NA is the numerical aperture; I f (λ i , r0) is the sidelobe light intensity in the field of view, is the central light intensity; r0 is the defined sidelobe range in the field of view, and r FWHM and r max are the lower and upper limits of the sidelobe range, respectively.

[0045] As an optimal solution for the large-field achromatic imaging device of the titanium dioxide metalens, in the large-field off-axis aberration correction module, during the optimization process of the point spread function with different off-axis degrees by using the exhaustive algorithm in combination with the angular spectrum theory, the focusing characteristics of the metalens at different off-axis degrees are calculated using the angular spectrum theory.

[0046] The expression for calculating the focusing characteristics of the metalens at different off-axis degrees using the angular spectrum theory is:

[0047]

[0048] Among them, I(x off , y off ; x, y) is the light intensity distribution of the off-axis point (x off , y off ) at (x, y); A(f x , f y ) is the angular spectrum of the light field near the exit surface of the metalens, which is calculated by the following formula:

[0049]

[0050] In the formula, f x , f y , f z are the frequency components along the x, y, and z directions respectively; U(x, y) represents the spherical wavefront of the off-axis point, u0 is the initial light intensity amplitude; l r is the distance between the off-axis point (x off , y off ) in the object plane and the point (x, y) on the lens; t(r) is the transmission function of the metasurface, is the circular domain function, φ SOM is the phase modulation amount of the metasurface; F[·] represents the Fourier transform.

[0051] The present invention has the following advantages:

[0052] First, solve the color aberration problem: When designing a broadband achromatic metalens, optimize the genetic algorithm and combine it with the Rayleigh-Sommerfeld diffraction formula. Based on the preset objective function of broadband achromatism, inversely design and iteratively optimize the phase distribution. This can compensate for the phase differences of light with different wavelengths, reduce the influence of dispersion, solve the problem of severe dispersion of traditional lenses and some metalenses in a wide wavelength band, achieve an achromatic imaging effect, and improve the accuracy of imaging colors.

[0053] Second, break through the diffraction limit: Through the inverse design and iterative optimization of the surface phase distribution of a TiO2 metalens by the genetic algorithm, obtain a single-wavelength super-diffraction TiO2 metalens according to the preset objective function of single-wavelength super-diffraction focusing. This process precisely regulates the phase, enables the light field to be efficiently focused at the target focal length, breaks through the traditional diffraction limit, improves the imaging resolution, and can clearly present tiny details.

[0054] Third, achieve large-field-of-view imaging: Utilize the achromatic super-diffraction phase distribution, and optimize the point spread functions with different off-axis degrees by combining the exhaustive algorithm with the angular spectrum theory. This effectively corrects the off-axis aberration in a large field of view, expands the effective imaging range, enables the metalens to maintain good imaging quality within a large field of view, and avoids blurred imaging and distortion in the edge region.

[0055] Fourth, improve the comprehensive imaging performance: Each technical means cooperates with each other. From obtaining the phase-amplitude correspondence relationship by constructing a simulation structure, to designing single-wavelength and broadband achromatic metalenses, and then to achieving large-field-of-view achromatic imaging, the imaging performance of the metalens is overall improved, solving the problems of low diffraction efficiency and small effective imaging range of traditional diffractive lenses in a wide wavelength band, and having a wide application prospect in many fields. Description of the Drawings

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can be obtained based on the provided drawings.

[0057] Figure 1 It is a schematic flowchart of a method for large-field-of-view achromatic imaging of a titanium dioxide metalens provided in Embodiment 1 of the present invention;

[0058] Figure 2 It is a schematic flowchart of the specific implementation of a method for large-field-of-view achromatic imaging of a titanium dioxide metalens provided in Embodiment 1 of the present invention;

[0059] Figure 3 It is a schematic diagram of the single-wavelength performance of the nano-units of a method for large-field-of-view achromatic imaging of a titanium dioxide metalens provided in Embodiment 1 of the present invention;

[0060] Figure 4 Schematic diagram of the single - wavelength one - dimensional simulation performance of the nano - lens for the achromatic imaging method of a titanium dioxide super - lens with a large field of view provided in Embodiment 1 of the present invention;

[0061] Figure 5 Schematic diagram of the performance of the nano - unit for the achromatic imaging method of a titanium dioxide super - lens with a large field of view provided in Embodiment 1 of the present invention;

[0062] Figure 6 Schematic diagram of the genetic algorithm process for the achromatic imaging method of a titanium dioxide super - lens with a large field of view provided in Embodiment 1 of the present invention;

[0063] Figure 7 Schematic diagram of the phase response principle of the TiO2 super - lens for the achromatic imaging method of a titanium dioxide super - lens with a large field of view provided in Embodiment 1 of the present invention;

[0064] Figure 8 Schematic diagram of the exhaustive - angular spectrum theory phase compensation process for the achromatic imaging method of a titanium dioxide super - lens with a large field of view provided in Embodiment 1 of the present invention;

[0065] Figure 9 Schematic diagram of the architecture of an achromatic imaging device of a titanium dioxide super - lens with a large field of view provided in Embodiment 2 of the present invention. Detailed implementation manners

[0066] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0067] Embodiment 1

[0068] Refer to Figure 1 、 Figure 2 and Figure 3 The embodiments of the present invention provide an achromatic imaging method for a titanium dioxide super - lens with a large field of view, including the following steps:

[0069] S1. Construct a simulation model of the super - lens nano - pillar unit according to the finite - difference time - domain method, and obtain the phase - amplitude correspondence relationship of the TiO2 nano - pillar unit under different sizes;

[0070] S2. According to the preset first objective function for single-wavelength super-diffraction focusing, use the genetic algorithm to perform inverse design on the surface phase distribution of the TiO2 superlens, and through iterative optimization, obtain a TiO2 superlens with single-wavelength super-diffraction;

[0071] S3. Based on the inverse design strategy of the TiO2 superlens with single-wavelength super-diffraction, optimize the genetic algorithm, combine the optimized genetic algorithm with the Rayleigh-Sommerfeld diffraction formula, and according to the broadband achromatic aberration preset second objective function, perform inverse design and iterative optimization on the surface phase distribution of the TiO2 superlens with single-wavelength super-diffraction again to obtain a TiO2 superlens with broadband achromatic aberration super-diffraction;

[0072] S4. Through the phase distribution of the TiO2 superlens with broadband achromatic aberration super-diffraction, use the exhaustive algorithm combined with the angular spectrum theory to optimize the point spread functions with different off-axis degrees to achieve achromatic aberration super-diffraction imaging within a large field of view.

[0073] In this embodiment, in step S1, the phase modulation effect of the TiO2 nanocolumns mainly depends on the propagation path of light in the nanocolumn structure and its relative delay. When the radius of the nanocolumn increases, the equivalent refractive index increases accordingly, thus prolonging the optical path of light in the propagation path and resulting in a greater phase delay. In the design of the TiO2 superlens, the height h and the radius R are two key parameters affecting the phase and amplitude, and their phase-amplitude modulation mechanism can be expressed as:

[0074]

[0075] where λ is the wavelength, n eff is the equivalent refractive index of the nanocolumn, h is the height of the nanocolumn, is the phase modulation, A is the amplitude modulation, t is the transmittance, U out is the outgoing light field modulated by the nanocolumn. The height h mainly affects the transmittance. Usually, h needs to be selected to find the best balance between phase and transmittance efficiency control, so that while maintaining a high transmittance, precise adjustment of R can achieve phase regulation from 0 to 2π, achieving high-efficiency optical performance.

[0076] Among them, based on this flexible adjustment method of light phase, precise control of the lens phase can be achieved, thus reaching the required target phase distribution, which can be expressed as:

[0077]

[0078] where and are the phase after optimization compensation and the desired target phase respectively.

[0079] Specifically, during the simulation of the nanocolumn unit, the geometric parameters of the nanostructure (such as radius, height, spacing, etc.) are systematically scanned by the finite-difference time-domain method. By solving the Maxwell's equations in the time domain, the optical properties such as the phase, transmittance, and reflectivity of the nano unit under different size and material combinations are captured. The simulation structure of the nanocolumn unit is as shown in Figure 4 (a) in. To achieve a broadband achromatic effect centered at a wavelength of 800 nm, the wavelength range from visible light to near-infrared light of 640 nm - 960 nm is scanned. The corresponding relationship between the phase and the transmission efficiency obtained is as shown in Figure 4 (b) in. The height of the nanocolumn is 700 nm, and the transmittance basically remains above 90% when the radius is in the range of 25 nm - 190 nm, and the phase change with the radius basically covers the range from 0 to 2π.

[0080] In this embodiment, in step S1, the process of obtaining the phase-amplitude correspondence of the TiO2 nanocolumn unit under different sizes:

[0081] According to the constructed simulation model of the TiO nanocolumn unit, simulation screening is carried out to obtain the phase amplitude modulation amount of the nanocolumn at the set wavelength. Based on the correspondence between the nanocolumn unit and the phase modulation amount, a wavelength-size-phase database of the nanocolumn unit is constructed.

[0082] Based on the wavelength-size-phase database, the genetic algorithm and the exhaustive algorithm are used to iteratively optimize the phase of the lens surface to obtain the required phase distribution. Then, according to the required phase distribution, the required size distribution of the nanocolumn unit is determined.

[0083] Specifically, when light interacts with the TiO2 nanocolumn, the high refractive index characteristic of TiO2 changes the propagation of light. According to the Maxwell's equations, when light irradiates the nanocolumn, it will generate induced charges and currents inside, which will in turn affect the electromagnetic field distribution and change the phase and amplitude of light. By constructing a simulation model of the nanocolumn unit and using numerical calculation methods such as the finite-difference time-domain method, the light propagation of nanocolumns of different sizes at the set wavelength is simulated. Continuously change the size parameters such as the radius and height of the nanocolumn, record the phase and amplitude changes after the light passes through, and select the corresponding phase amplitude modulation amount through a large number of simulation calculations. Organize and store these data according to the wavelength, nanocolumn size, and phase information to construct a wavelength-size-phase database. This database integrates the phase information of the nanocolumn at different wavelengths and sizes, provides comprehensive data support for the design of the superlens, and facilitates quickly querying the nanocolumn size that meets specific phase requirements.

[0084] Among them, the genetic algorithm simulates biological evolution. The phase distribution on the lens surface is regarded as an individual, represented by the size parameters of the nanocolumns. The fitness of the individual is evaluated by defining fitness functions such as focusing intensity and achromatic performance. Individuals with high fitness are selected for crossover and mutation operations to generate new individuals, and through multiple generations of iteration, the optimal phase distribution is gradually found. The exhaustive algorithm traverses all possible combinations of nanocolumn sizes, calculates the phase distribution and imaging performance indicators of each combination, and selects the optimal combination after comparison. By combining the advantages of both, the required phase distribution can be obtained efficiently. According to the obtained required phase distribution, the corresponding nanocolumn size is queried in the wavelength-size-phase database, and for the phase requirements at each position on the lens surface, the corresponding nanocolumn size is determined, thus completing the conversion from phase design to nanocolumn size design and providing specific parameters for the preparation of the superlens.

[0085] In this embodiment, in step S2, in the process of obtaining the single-wavelength super-diffraction TiO2 superlens, the optical response of the phase on the surface of the TiO2 superlens is iteratively optimized by combining the genetic algorithm with the Rayleigh-Sommerfeld diffraction formula. When the phase on the surface of the TiO2 superlens satisfies the convergence condition that it does not change after several consecutive iterations, the iterative optimization is stopped.

[0086] In the process of obtaining the broadband achromatic super-diffraction TiO2 superlens, the phase on the surface of the TiO2 superlens is iteratively optimized and stopped when the same convergence condition is satisfied.

[0087] Specifically, in the optimized design of the TiO2 nano-unit superlens, the arrangement pattern, size parameters, etc. of the nano-units can be used as the genes of the genetic algorithm, and the optical performance of the superlens (such as focal intensity, wavefront phase error, etc.) can be used as the measurement standard of the fitness function. Refer to Figure 6 , through continuous selection, crossover, and mutation operations, the genetic algorithm can independently explore and optimize the structural design to improve the imaging quality and light field regulation ability of the superlens.

[0088] The present invention is based on the relationship between the phase response and transmission efficiency obtained by scanning the wavelength of 780 nm as shown in Figure 3 . The genetic algorithm is used to search for the optimal radius distribution to achieve the optimal phase distribution, and the FDTD simulation model is used to calculate the fitness. As shown in Figure 5 , to evaluate the focusing effect of each set of radius parameters, so that the optimized phase distribution maximally approaches the target phase distribution

[0089]

[0090] Among them, the focusing phase of the ideal lens is to ensure that the wavefronts at different positions can achieve constructive interference at the axial focal length, so that the focusing light intensity reaches the maximum value. is for higher-resolution phase compensation, while represents the ideal phase distribution achieved under high-resolution focusing. By precisely controlling the phase distribution, it is ensured that the incident waves at each position converge at the focus with consistent phases during propagation, ultimately achieving the most ideal focusing effect. A focal length is preset to maximize the central focusing light intensity at the focal length position for the current wavelength. Therefore, the first objective function and constraints for a single wavelength are as follows:

[0091]

[0092] In the formula, is the central light field intensity at the target focal length; R = [R1, R2, …, R n is the set of nano-unit radii; n is the number of nano-units; R i is the radius of the i-th nano-pillar; R min and R max are the value ranges of the nano-pillar radii; in which p is the spacing between adjacent nano-pillars in a specified direction, and are the coordinates of the corresponding nano-pillar in the specified direction.

[0093] Among them, the radius range is obtained under the nano-pillar spacing p. During the optimization process, it is necessary to ensure that the change in the radius can cover the phase range from 0 to 2π to guarantee the integrity of the phase distribution.

[0094] In this embodiment, in step S3, according to the reverse design strategy of the single-wavelength super-diffraction TiO2 superlens, the genetic algorithm is optimized. Combining the optimized genetic algorithm and the Rayleigh-Sommerfeld diffraction formula, the surface phase distribution of the TiO2 superlens is reversely designed according to the second objective function for broadband achromatism, and iterative optimization is performed to obtain a broadband achromatic super-diffraction TiO2 superlens.

[0095] Specifically, when performing multi-wavelength optimization, phase optimization needs to be carried out at discrete position points to ensure a stable achromatic effect under multi-wavelength conditions. In order to further shorten the FDTD simulation time in the present invention, a more accurate Rayleigh-Sommerfeld transmission formula can be used to approximately calculate the phase response during the optimization process to quickly evaluate the influence of different phase distributions on the multi-wavelength focusing effect. Through the rapid response of the Rayleigh-Sommerfeld formula, the computational cost of each optimization iteration can be significantly reduced. After optimizing the ideal phase distribution, simulation is used for final verification and accuracy evaluation to ensure the accuracy of the optimization results under actual physical conditions.

[0096] To shorten the simulation time and ensure the simulation accuracy, a model of the field strength distribution of the metalens was established according to the Rayleigh-Sommerfeld diffraction formula. This model can simulate the focusing process of an arbitrary NA metalens based on the phase distribution of the source plane. After the incident light beam is modulated by the wavefront of the metalens, constructive interference is formed at the focal point, thus achieving efficient focusing. As Figure 7 shown, the phase distribution on the exit surface of the metalens is directly considered as the phase U1(x m ’, y n ’) of the source plane, that is, the phase distribution modulated by the metalens is directly used to simulate the propagation process of light waves, so that the light beam finally converges at the center position of the focal plane. According to the Rayleigh-Sommerfeld diffraction theory, the discrete sampling phase of the metalens can be expressed as the following integral formula during the propagation process:

[0097]

[0098] In the formula, U2(x, y) is the field strength distribution of the focal plane, U1(x’, y’) is the field strength phase distribution of the source plane, k is the wave number, z is the distance from the source plane to the focal plane, that is, the focal length, Δx’ and Δy’ are the sampling intervals of the phase distribution on the source plane, corresponding to the intervals of the nano-units on the metalens, and r mn is the distance from a point on the source plane to a point on the focal plane.

[0099] Due to the existence of chromatic aberration, it seriously affects the imaging performance of the lens under non-monochromatic light illumination and limits its application scope in the fields of optical focusing and imaging. To overcome this problem, the present invention generalizes and optimizes the genetic algorithm inverse design theory, successfully expanding it from the single-wavelength field to the multi-wavelength category, and thus designs a broadband achromatic TiO2 metalens.

[0100] In the multi-wavelength optimization, first, the phase distribution and transmission efficiency at different wavelengths are accurately scanned, and the corresponding relationship between the nano-unit size and the phase response at different wavelengths is established, as Figure 5 shown. The lens radius is set to 400 μm and the focal length is 500 μm. Combining the genetic algorithm with the Rayleigh-Sommerfeld transmission formula for optimization, the phase distribution at each wavelength is effectively compensated, so that the light intensity is maximized at the focusing position. Therefore, the achromatic super-diffraction target phase profile is:

[0101]

[0102] In the formula, is the phase profile to achieve multi-wavelength super-resolution focusing, is the compensation phase to achieve super-resolution focusing at different wavelengths, C(λ i , r) is the achromatic compensation phase for focusing at different wavelengths, and The achromatic focusing phase in the ideal state. To establish an effective super-resolution achromatic optimization model, the second objective function and constraints are optimized as follows:

[0103]

[0104] In the formula, I fr＝0 (λ i , r) is the light intensity at the center point at the target focal length, is the phase distribution to be optimized in the model, FWHW(λ i ) is the full width at half maximum corresponding to the wavelength, and it is required to be lower than the diffraction limit. r0 defines the range of sidelobes in the field of view, and I f (λ i ) is the light intensity of the sidelobes in the field of view. The goal is to make the sidelobe light intensity as low as possible, less than 0.2 times the central peak light intensity, in order to achieve higher focusing resolution and focusing efficiency.

[0105] In this embodiment, in step S4, during the optimization process of the point spread function with different off-axis degrees by using the exhaustive algorithm combined with the angular spectrum theory, the focusing characteristics of the superlens at different off-axis degrees are calculated using the angular spectrum theory, so as to achieve achromatic super-diffraction imaging within a large field of view.

[0106] Specifically, the present invention uses the angular spectrum (Angular Spectrum, AS) theory combined with the exhaustive algorithm to compensate and correct the off-axis aberration in the achromatic lens. The angular spectrum theory has unique accuracy and efficiency advantages in dealing with the PSF, and is particularly suitable for high-NA and wide-field imaging systems. Its core idea is to decompose the light field into plane waves with different angles and frequencies, and accurately calculate the phase change of the wavefront propagation at each angle. Through this method, the angular spectrum theory can clearly depict the propagation path and phase evolution of off-axis light, so as to better describe the complex phase structure and effectively deal with the off-axis aberration problem under a wide field of view. The expression for calculating the focusing characteristics of the superlens at different off-axis degrees using the angular spectrum theory is:

[0107]

[0108] where, I(x off , y off ; x, y) is the light intensity distribution of the off-axis point (x off , y off ) at (x, y); A(f x , f y ) is the angular spectrum of the light field near the exit surface of the superlens, which is calculated by the following formula:

[0109]

[0110] In the formula, f x , fy , f z are the frequency components along the x, y, and z directions respectively; U(x, y) represents the spherical wavefront of an off-axis point, and u0 is the initial light intensity amplitude; l r is the distance between the off-axis point (x off , y off ) in the object plane and the point (x, y) on the lens; t(r) is the transmission function of the metasurface, is the circular domain function, and φ SOM is the phase modulation amount of the metasurface; F[·] represents the Fourier transform.

[0111] When designing a broadband achromatic large field-of-view metalens, to achieve super-resolution imaging in a wide field of view, the present invention further performs compensation optimization of the binary phase (0, π) based on the optimized achromatic phase to correct off-axis aberration and maintain resolution, as shown in Fig. 8. First, the compensated phase distribution is discretized into n rings. Since the phase values of each ring are independent of each other, a library containing 2 n kinds of binary phase distributions is established, and combined with the compensated phase and the achromatic phase, each possible binary phase distribution is screened through an exhaustive algorithm and the angular spectrum theory, thereby improving the off-axis aberration correction performance and imaging resolution of the system.

[0112] To prove the effect of the present invention. In practical applications, the following verification is carried out through professional optical simulation software (such as FDTD Solutions, etc.) and experimental equipment.

[0113] Verification of single-wavelength super-diffraction focusing effect

[0114] Example settings: The central wavelength is set to 780 nm, the metalens aperture is 660 μm, and the focal length is 400 μm. The height of the nanorods is fixed at 700 nm, the radius ranges from 25 nm to 190 nm, and the number of nanorod units is 1650.

[0115] Optimization process: According to the preset objective function of single-wavelength super-diffraction focusing, the genetic algorithm is used to iteratively optimize the surface phase distribution of the TiO2 metalens. After 500 iterations, the algorithm converges.

[0116] Data results: Before optimization, the central light field intensity If(λ) at the target focal length is 100 (relative unit), and after optimization, If(λ) is increased to 140 (relative unit), an increase of 1.4 times. At the same time, the full width at half maximum (FWHM) of the focused spot is reduced from 934 nm before optimization to 723 nm, approaching the theoretical diffraction limit (about 742 nm, according to the Rayleigh criterion FWHM = 0.61λ / NA, assuming the numerical aperture NA = 0.64), which proves that the single-wavelength super-diffraction focusing effect is significant and can effectively improve the imaging resolution.

[0117] Verification of broadband achromatic effect

[0118] Example settings: Considering the wavelength range of 640nm - 960nm, the parameters of the metalens are the same as those in the single-wavelength example.

[0119] Optimization process: Based on the inverse design strategy of the single-wavelength super-diffractive TiO2 metalens, optimizing the genetic algorithm and combining with the Rayleigh - Sommerfeld diffraction formula, the surface phase distribution of the metalens is iteratively optimized according to the preset objective function of broadband achromatism. After 1800 iterations, the convergence condition is reached.

[0120] Data results: Before optimization, the focal position deviation was large at different wavelengths, with the maximum deviation reaching 50μm. After optimization, within the entire wavelength range, the focal position deviation is controlled within 5μm, basically achieving the achromatic effect. At the same time, the full width at half maximum (FWHM) at each wavelength is lower than the diffraction limit, and the ratio of the sidelobe intensity If(λi) to the central peak intensity Ifr=0(λi,r) within the field of view is less than 0.2, effectively improving the focusing resolution and imaging quality.

[0121] Verification of large field of view achromatic super-diffractive imaging effect

[0122] Example settings: Based on the above broadband achromatic metalens, the off-axis angle range is set from -15° to 15°.

[0123] Optimization process: Using the achromatic super-diffractive phase distribution, the point spread function at different off-axis degrees is optimized by means of the exhaustive algorithm combined with the angular spectrum theory. 2n (n is the number of discretized phase rings, here n = 5) binary phase distributions at each off-axis angle are screened.

[0124] Data results: Before optimization, the imaging in the edge area of the large field of view was severely blurred and the resolution was extremely low. After optimization, within the entire large field of view, the imaging clarity has been significantly improved. Taking the off-axis angle of 15° as an example, the energy concentration of the point spread function has increased by 30%, and the difference in resolution between the edge area and the central area is less than 10%, effectively achieving achromatic super-diffractive imaging within the large field of view and expanding the effective imaging range of the metalens.

[0125] It should be noted that the method of the embodiments of the present disclosure can be executed by a single device, such as a computer or a server, etc. The method of this embodiment can also be applied to a distributed scenario and completed by multiple devices cooperating with each other. In this case of a distributed scenario, one of the multiple devices can only execute one or more steps of the method of the embodiments of the present disclosure, and these multiple devices will interact with each other to complete the method for large field of view achromatic imaging of a titanium dioxide metalens.

[0126] It should be noted that some embodiments of the present disclosure have been described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the above embodiments and still achieve the desired results. Additionally, the processes depicted in the drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0127] Embodiment 2

[0128] See Figure 9 , Embodiment 2 of the present invention also provides a titanium dioxide superlens large field of view achromatic imaging device, adopting a titanium dioxide superlens large field of view achromatic imaging method of the above embodiment, including:

[0129] A phase optimization and size mapping module 001, configured to construct a simulation model of the superlens nanorod unit according to the finite-difference time-domain method, and obtain the phase-amplitude correspondence relationship of the TiO2 nanorod unit under different sizes;

[0130] A single-wavelength super-diffraction TiO2 superlens acquisition module 002, configured to perform inverse design on the surface phase distribution of the TiO2 superlens according to a single-wavelength super-diffraction focusing preset first objective function by using a genetic algorithm, and obtain a single-wavelength super-diffraction TiO2 superlens through iterative optimization;

[0131] A broadband achromatic super-diffraction TiO2 superlens acquisition module 003, configured to optimize the genetic algorithm based on the inverse design strategy of the single-wavelength super-diffraction TiO2 superlens, combine the optimized genetic algorithm with the Rayleigh-Sommerfeld diffraction formula, and perform inverse design and iterative optimization on the surface phase distribution of the single-wavelength super-diffraction TiO2 superlens again according to a broadband achromatic preset second objective function to obtain a broadband achromatic super-diffraction TiO2 superlens;

[0132] A large field of view off-axis aberration correction module 004, configured to optimize the point spread function with different off-axis degrees by using an exhaustive algorithm combined with the angular spectrum theory through the phase distribution of the broadband achromatic super-diffraction TiO2 superlens, so as to achieve achromatic super-diffraction imaging within a large field of view.

[0133] In this embodiment, the phase optimization and size mapping module 001 includes:

[0134] A wavelength-size-phase database construction sub-module 101, configured to perform simulation screening according to the constructed TiO nanorod unit simulation model to obtain the phase amplitude modulation amount of the nanorod under a set wavelength; construct a wavelength-size-phase database of the nanorod unit according to the correspondence relationship between the nanorod unit and the phase modulation amount;

[0135] The nano-column unit size distribution determination sub-module 102 is configured to iteratively optimize the phase of the lens surface based on the wavelength-size-phase database by using a genetic algorithm and an exhaustive algorithm to obtain the required phase distribution; and then determine the required nano-column unit size distribution according to the required phase distribution.

[0136] In this embodiment, in the single-wavelength super-diffraction TiO2 superlens acquisition module 002, the optical response of the phase of the TiO2 superlens surface is iteratively optimized by combining a genetic algorithm with the Rayleigh-Sommerfeld diffraction formula. When the phase of the TiO2 superlens surface satisfies the convergence condition that it does not change after several consecutive iterations, the iterative optimization is stopped.

[0137] In the broadband achromatic super-diffraction TiO2 superlens acquisition module 003, during the process of obtaining the broadband achromatic super-diffraction TiO2 superlens, the phase of the TiO2 superlens surface is iteratively optimized and stopped when the same convergence condition is satisfied.

[0138] In this embodiment, in the single-wavelength super-diffraction TiO2 superlens acquisition module 002, the expression of the first objective function preset according to the single-wavelength super-diffraction focusing is:

[0139]

[0140] In the formula, is the central light field intensity at the target focal length; R = [R1, R2,..., R n is the set of nano-unit radii; n is the number of nano-units; R i is the radius of the i-th nano-column; R min and R max are the value ranges of the nano-column radii; where p is the spacing between adjacent nano-columns in the specified direction, and are the coordinates of the corresponding nano-column in the specified direction.

[0141] In this embodiment, in the broadband achromatic super-diffraction TiO2 superlens acquisition module 003, the expression of the second objective function preset according to the broadband achromatism is:

[0142]

[0143] In the formula, is the central light intensity at the target focal length; is the phase distribution to be optimized; FWHM(λ i ) is the full width at half maximum at the corresponding wavelength, NA is the numerical aperture; I f (λ i, r0) is the sidelobe light intensity within the field of view, is the central light intensity; r0 is the defined sidelobe range within the field of view, r FWHM and r max are respectively the lower and upper limits of the sidelobe range.

[0144] In this embodiment, in the large field of view off-axis aberration correction module 004, during the optimization process of the point spread function with different off-axis degrees by using the exhaustive algorithm in combination with the angular spectrum theory, the focusing characteristics of the metalens at different off-axis degrees are calculated using the angular spectrum theory.

[0145] The expression for calculating the focusing characteristics of the metalens at different off-axis degrees using the angular spectrum theory is:

[0146]

[0147] where, I(x off , y off ; x, y) is the light intensity distribution of the off-axis point (x off , y off ) at (x, y); A(f x , f y ) is the angular spectrum of the light field near the exit surface of the metalens, which is calculated by the following formula:

[0148]

[0149] In the formula, f x , f y , f z are respectively the frequency components along the x, y, and z directions; U(x, y) represents the spherical wavefront of the off-axis point, u0 is the initial light intensity amplitude; l r is the distance between the off-axis point (x off , y off ) in the object plane and the point (x, y) on the lens; t(r) is the transmission function of the metasurface, is the circular domain function, φ SOM is the phase modulation amount of the metasurface; F[·] represents the Fourier transform.

[0150] It should be noted that the information interaction, execution process, etc. between the above device modules, since they are based on the same concept as the method embodiment in Embodiment 1 of the present application, the technical effects brought by them are the same as those of the method embodiment of the present application. For the specific content, reference can be made to the description in the method embodiment shown above in the present application, and details are not described herein again.

[0151] Embodiment 3

[0152] Embodiment 3 of the present invention provides a non-transitory computer-readable storage medium, in which program code for a method of large-field achromatic imaging using a titanium dioxide superlens is stored. The program code includes instructions for executing the method of large-field achromatic imaging using a titanium dioxide superlens according to Embodiment 1 or any possible implementation thereof.

[0153] The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server or a data center that integrates one or more available media. The available medium can be a magnetic medium (for example, a floppy disk, a hard disk, or a magnetic tape), an optical medium (for example, a DVD), or a semiconductor medium (for example, a solid-state disk (SSD)).

[0154] Embodiment 4

[0155] Embodiment 4 of the present invention provides an electronic device, including: a memory and a processor;

[0156] The processor and the memory communicate with each other through a bus; the memory stores program instructions executable by the processor, and the processor can execute the method of large-field achromatic imaging using a titanium dioxide superlens according to Embodiment 1 or any possible implementation thereof by calling the program instructions.

[0157] Specifically, the processor can be implemented by hardware or by software. When implemented by hardware, the processor can be a logic circuit, an integrated circuit, etc.; when implemented by software, the processor can be a general-purpose processor that is implemented by reading software code stored in the memory. The memory can be integrated in the processor or can exist independently outside the processor.

[0158] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the processes or functions according to the embodiments of the present invention are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable systems. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center by wire (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wirelessly (such as infrared, wireless, microwave, etc.).

[0159] Obviously, those skilled in the art should understand that the above-mentioned modules or steps of the present invention can be implemented by a general-purpose computing system. They can be concentrated on a single computing system or distributed on a network composed of multiple computing systems. Optionally, they can be implemented by program codes executable by the computing system. Thus, they can be stored in a storage system and executed by the computing system. And in some cases, the steps shown or described can be executed in a sequence different from that here, or they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module for implementation. In this way, the present invention is not limited to any specific combination of hardware and software.

[0160] Although the present invention has been described in detail above with general descriptions and specific embodiments, on the basis of the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A titanium dioxide superlens large field achromatic imaging method, characterized in that: include: The simulation model of the superlens nanocolumn unit is constructed according to the finite-difference time-domain method, and the phase-amplitude correspondence of the TiO2 nanocolumn unit at different sizes is obtained; According to the preset first objective function of single-wavelength super-diffraction focusing, the surface phase distribution of TiO2 super-lens is reversely designed using genetic algorithm, and the single-wavelength super-diffraction TiO2 super-lens is obtained through iterative optimization. Based on the reverse design strategy of the single-wavelength super-diffraction TiO2 super-lens, the genetic algorithm is optimized, and the optimized genetic algorithm is combined with the Rayleigh-Sommerfeld diffraction formula. According to the broadband achromatic preset second objective function, the surface phase distribution of the single-wavelength super-diffraction TiO2 super-lens is reversely designed and iteratively optimized again to obtain a broadband achromatic super-diffraction TiO2 super-lens; Through the phase distribution of the broadband achromatic super-diffraction TiO2 super-lens, an exhaustive algorithm is used in combination with angular spectrum theory to optimize the point spread functions of different off-axis degrees to achieve achromatic super-diffraction imaging within a large field of view.

2. A titanium dioxide superlens large field achromatic imaging method according to claim 1, characterized in that: The process of obtaining the phase-amplitude correspondence of TiO2 nanocolumn units at different sizes: Perform simulation screening according to the constructed TiO nanocolumn unit simulation model to obtain the phase amplitude modulation amount of the nanocolumn at a set wavelength; and construct a wavelength-size-phase database of the nanocolumn unit based on the corresponding relationship between the nanocolumn unit and the phase modulation amount; Based on the wavelength-size-phase database, the lens surface phase is iteratively optimized using a genetic algorithm and an exhaustive algorithm to obtain a desired phase distribution; and then the desired nanocolumn unit size distribution is determined based on the desired phase distribution.

3. A titanium dioxide superlens large field achromatic imaging method according to claim 1, characterized in that: In the process of obtaining a single-wavelength super-diffraction TiO2 super-lens, the optical response of the surface phase of the TiO2 super-lens is iteratively optimized by combining a genetic algorithm with a Rayleigh-Sommerfeld diffraction formula, and the iterative optimization is stopped when the surface phase of the TiO2 super-lens meets a convergence condition that it does not change after several consecutive iterations; In the process of obtaining a broadband achromatic super-diffraction TiO2 super-lens, the surface phase of the TiO2 super-lens is iteratively optimized and stopped when the same convergence condition is met.

4. A titanium dioxide superlens large field achromatic imaging method according to claim 1, characterized in that: The expression of the first objective function preset according to single-wavelength super-diffraction focusing is: In the formula, is the central light field intensity at the target focal length; R=[R1,R2,…,R n ] is the radius set of nanometer units; n is the number of nanometer units; R i is the radius of the ith nanorod; R min and R max is the value range of the nanocolumn radius; where p is the spacing between adjacent nanopillars in a specified direction, and is the coordinate of the corresponding nanorod in the specified direction.

5. A titanium dioxide superlens large field achromatic imaging method according to claim 4, characterized in that: The expression of the second objective function preset according to broadband achromatism is: In the formula, is the light intensity at the center point of the target focal length; is the phase distribution to be optimized; FWHM(λ i ) is the full width at half maximum at the corresponding wavelength, NA is the numerical aperture; I f (λ i ,r0) is the side lobe intensity in the field of view, is the central light intensity; r0 is the side lobe range within the defined field of view, r FWHM and r max are the lower and upper limits of the sidelobe range respectively.

6. A titanium dioxide superlens large field achromatic imaging method according to claim 5, characterized in that: The exhaustive algorithm is combined with the angular spectrum theory to optimize the point spread function at different off-axis degrees. The angular spectrum theory is used to calculate the focusing characteristics of the metalens at different off-axis degrees. The expression for calculating the focusing characteristics of the metalens at different off-axis degrees using angular spectrum theory is: Among them, I(x off ,y off ; x,y) is the off-axis point (x off ,y off ) light intensity distribution at (x,y); A(f x ,f y ) is the angular spectrum of the light field near the exit surface of the superlens, which is calculated by the following formula: In the formula, f x ,f y ,f z are the frequency components along the x, y, and z directions respectively; U(x, y) represents the spherical wavefront at the off-axis point, u0 is the initial light intensity amplitude; l r is the off-axis point in the object plane (x off ,y off ) is the distance between the point (x, y) on the lens; t(r) is the transmission function of the metasurface, is a circular domain function, φ SOM is the phase modulation of the metasurface; F[·] represents Fourier transform.

7. A titanium dioxide superlens large field achromatic imaging device, characterized in that: A titanium dioxide superlens large field achromatic imaging method according to any one of claims 1 to 6, comprising: Phase optimization and size mapping module, used to construct a simulation model of a superlens nanocolumn unit according to the finite-difference time-domain method, and obtain the phase-amplitude correspondence of the TiO2 nanocolumn unit at different sizes; A single-wavelength super-diffraction TiO2 super-lens acquisition module is used to preset a first objective function according to single-wavelength super-diffraction focusing, use a genetic algorithm to reversely design the surface phase distribution of the TiO2 super-lens, and obtain a single-wavelength super-diffraction TiO2 super-lens through iterative optimization; A broadband achromatic super-diffraction TiO2 super-lens acquisition module is used to optimize the genetic algorithm based on the reverse design strategy of the single-wavelength super-diffraction TiO2 super-lens, combine the optimized genetic algorithm with the Rayleigh-Sommerfeld diffraction formula, and according to the broadband achromatic preset second objective function, reversely design and iteratively optimize the surface phase distribution of the single-wavelength super-diffraction TiO2 super-lens again to obtain a broadband achromatic super-diffraction TiO2 super-lens; The large-field-of-view off-axis aberration correction module is used to optimize the point spread functions of different off-axis degrees through the phase distribution of the broadband achromatic super-diffraction TiO2 super-lens, using an exhaustive algorithm combined with angular spectrum theory, so as to achieve achromatic super-diffraction imaging within a large field of view.

8. A titanium dioxide superlens large field achromatic imaging device according to claim 7, characterized in that: The phase optimization and size mapping module includes: The wavelength-size-phase database construction submodule is used to perform simulation screening according to the constructed TiO nanocolumn unit simulation model to obtain the phase amplitude modulation amount of the nanocolumn at a set wavelength; and to construct a wavelength-size-phase database of the nanocolumn unit according to the corresponding relationship between the nanocolumn unit and the phase modulation amount; The nanocolumn unit size distribution determination submodule is used to iteratively optimize the lens surface phase based on the wavelength-size-phase database using a genetic algorithm and an exhaustive algorithm to obtain the required phase distribution; and then determine the required nanocolumn unit size distribution based on the required phase distribution.

9. A titanium dioxide superlens large field achromatic imaging device according to claim 7, characterized in that: In the single-wavelength super-diffraction TiO2 super-lens acquisition module, the optical response of the surface phase of the TiO2 super-lens is iteratively optimized by combining a genetic algorithm with a Rayleigh-Sommerfeld diffraction formula, and when the surface phase of the TiO2 super-lens satisfies a convergence condition that it does not change after several consecutive iterations, the iterative optimization is stopped; In the broadband achromatic super-diffraction TiO2 super-lens acquisition module, in the process of obtaining the broadband achromatic super-diffraction TiO2 super-lens, the surface phase of the TiO2 super-lens is iteratively optimized and stopped when the same convergence conditions are met.

10. A titanium dioxide superlens large field achromatic imaging device according to claim 9, characterized in that: In the single-wavelength super-diffraction TiO2 super-lens acquisition module, the expression of the first objective function preset according to the single-wavelength super-diffraction focusing is: In the formula, is the central light field intensity at the target focal length; R=[R1,R2,…,R n ] is the radius set of nanometer units; n is the number of nanometer units; R i is the radius of the ith nanorod; R min and R max is the value range of the nanocolumn radius; where p is the spacing between adjacent nanopillars in a specified direction, and is the coordinate of the corresponding nanopillar in the specified direction; In the broadband achromatic super-diffraction TiO2 superlens acquisition module, the expression of the second objective function preset according to the broadband achromatic is: In the formula, is the light intensity at the center point of the target focal length; is the phase distribution to be optimized; FWHM(λ i ) is the full width at half maximum at the corresponding wavelength, NA is the numerical aperture; I f (λ i ,r0) is the side lobe intensity in the field of view, is the central light intensity; r0 is the side lobe range within the defined field of view, r FWHM and r max are the lower and upper limits of the sidelobe range respectively; In the large-field off-axis aberration correction module, an exhaustive algorithm is used in combination with angular spectrum theory to optimize the point spread function at different off-axis degrees, and the angular spectrum theory is used to calculate the focusing characteristics of the metalens at different off-axis degrees; The expression for calculating the focusing characteristics of the metalens at different off-axis degrees using angular spectrum theory is: Among them, I(x off ,y off ; x,y) is the off-axis point (x off ,y off ) light intensity distribution at (x,y); A(f x ,f y ) is the angular spectrum of the light field near the exit surface of the superlens, which is calculated by the following formula: In the formula, f x ,f y ,f z are the frequency components along the x, y, and z directions respectively; U(x, y) represents the spherical wavefront at the off-axis point, u0 is the initial light intensity amplitude; l r is the off-axis point in the object plane (x off ,y off ) is the distance between the point (x, y) on the lens; t(r) is the transmission function of the metasurface, is a circular domain function, φ SOM is the phase modulation of the metasurface; F[·] represents Fourier transform.

Images