Meta-structure axicon and design method thereof, imaging system composed of meta-structure axicon and imaging method

Abstract

The invention belongs to the technical field of super-structure lenses, and particularly relates to a super-structure axicon and a design method thereof, an imaging system composed of the super-structure axicon and an imaging method.The design method comprises the steps that a two-dimensional unit structure simulation model of a concentric ring structure is constructed, simulation calculation is conducted on the two-dimensional unit structure simulation model, and a simulation result is obtained; obtaining the complex amplitude transmittance of the two-dimensional unit structure to the incident light; according to the configuration of each two-dimensional unit structure and the limitation of the metasurface processing technology, screening the two-dimensional unit structures meeting the processing technology requirements, and integrating the two-dimensional unit structures into a unit structure library; and according to the two-dimensional unit structure in the unit structure library and the target phase surface, constructing a two-dimensional cross section of the superstructure axicon based on the concentric ring structure, and rotating the two-dimensional cross section around the optical axis of the superstructure axicon to obtain a three-dimensional structure of the superstructure axicon. According to the invention, the wide-spectrum consistency of the point spread function of the Bessel beam generated by the super-structure axicon is utilized, and the non-blind image restoration algorithm is combined, so that the chromatic aberration is eliminated, and the image definition is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metalens, and specifically relates to a metaaxon and a design method thereof, an imaging system composed of the metaaxon, and an imaging method. Background Art

[0002] Meta-lenses have the advantages of being light, thin, simplified in structure, low in cost, and having a high degree of freedom in controlling the light field. Its weight is negligible compared to traditional lenses, so it can effectively reduce the overall weight of the product. This lightweight feature is crucial in mobile devices and aerospace fields, and can significantly reduce energy consumption and improve the portability of the device. Traditional catadioptric optical systems usually require multiple lens groups to achieve the required optical performance, while meta-lenses can integrate all functions on one or two meta-surfaces. The simplified structure not only reduces the complexity of the product, but also reduces the disadvantage of the larger product volume caused by too many lenses, making the device more compact. In terms of optical performance, through the fine sub-wavelength structural size design, meta-lenses can achieve independent and free control of the main light field parameters such as amplitude, phase, and polarization, thereby integrating multiple light control functions. Thanks to the above advantages, meta-lens technology has received continuous attention from optical practitioners in the past decade, and has broad application prospects in consumer electronics, security monitoring, automotive electronics, optical communications, AR / VR and other fields.

[0003] Although metalenses have excellent integration performance, the chromatic aberration problem they exhibit seriously restricts the further development and application of metalenses. Metalenses based on monochrome design have dispersion behavior similar to that of diffraction lenses, and their focal length is approximately inversely proportional to the wavelength. Therefore, a visible light metalens with a focal length of centimeters will produce at least several millimeters of defocus, which is unacceptable for the design goal of near-diffraction limit imaging. At present, the achromatic design of metalenses is mainly based on phase dispersion control engineering, that is, the design of metaatoms for optimal phase matching of a wide spectrum. In this method, there is a strict mutual constraint relationship between the aperture, numerical aperture, and wavelength of the metalens, so that the aperture of the current finished device is generally only on the order of hundreds of wavelengths, which still cannot meet most application requirements. Although the methods such as variable height structure achromatism and quasi-continuous spectrum achromatism developed on this basis have alleviated this problem to a certain extent, it is still difficult to achieve an order-of-magnitude increase in the aperture of the achromatic metalens, and it also introduces new problems such as low focusing efficiency and difficulty in processing micro-nano structures.

[0004] Now consider using image processing to eliminate the chromatic aberration of the meta-lens. Formula 1 is the imaging model of the meta-lens:

[0005] in, is the focal length of the metalens, is the image collected by the meta-lens; [ , ] is the transmission band of the meta-lens; The wavelength exist The point spread function at ; is the convolution symbol; The wavelength of the incident light is The ideal image when ; B is the intensity of the zero-order diffraction light of the meta-lens, which is a constant and can be obtained from The total intensity is calculated.

[0006] For an imaging system composed of a meta-lens, if chromatic aberration is compensated by data processing, it is equivalent to knowing , , the diffraction efficiency of the meta-lens (B can be obtained), , , . Solution For the focal length of the lens f An image collected at , even if it is known , but due to along with As the wavelength changes, the known quantity of this problem is far less than the unknown quantity, so it cannot be solved. For the point-focusing meta-lens, the focused spot will diverge rapidly as the wavelength changes, that is, right Dependency sensitivity, such as Figure 1a As shown, it is difficult to use image processing methods to solve the problem of image quality degradation caused by chromatic aberration when imaging with a point-focusing meta-lens. Summary of the invention

[0007] In view of this, the present invention aims to provide a metaaxon and a design method thereof, an imaging system composed of the metaaxon, and an imaging method, so as to solve the problem that metalens with an aperture of the order of thousands of wavelengths or more is difficult to achieve continuous spectrum achromatic imaging.

[0008] To achieve the above object, the technical solution created by the present invention is implemented as follows: A method for designing a metaaxon, wherein the designed metaaxon is used to generate a Bessel beam, comprising the following steps: S1: construct a two-dimensional unit structure simulation model of a concentric ring structure, perform simulation calculation on the two-dimensional unit structure simulation model, and obtain the complex amplitude transmittance of the two-dimensional unit structure to the incident light; wherein the cross section of the concentric ring structure along the diameter forms a two-dimensional unit structure of different configurations, and the two-dimensional unit structure is at the sub-wavelength level; S2: According to the configuration of each two-dimensional unit structure and the limitations of the supersurface processing technology, the two-dimensional unit structure that meets the requirements of the supersurface processing technology is screened and integrated into the unit structure library; S3: Construct a two-dimensional cross-section of a metaaxon based on a concentric ring structure according to the two-dimensional unit structure in the unit structure library and the target phase plane, and rotate the two-dimensional cross-section around the optical axis of the metaaxon to obtain a three-dimensional structure of the metaaxon.

[0009] Furthermore, in step S1, the structural dimensions of the two-dimensional unit structure simulation model are determined according to the working parameters of the metaaxon.

[0010] Furthermore, after determining the structural dimensions of the two-dimensional unit structure simulation model, the finite element analysis method is used to establish a calculation model of the scattering field. The TE wave and TM wave are taken as the background field, and the complex amplitude transmittance of different two-dimensional unit structures is solved according to the Helmholtz equation.

[0011] Furthermore, the transmission band of the meta-axon is set to l l to l u , and set the design wavelength of the two-dimensional unit structure to l 0, l 0 2 = l l l u ,but: According to the minimum operating wavelength l l Determining the cell width for a 2D cell structure simulation model L , and constrain L ≤ l l ; Minimum processing size according to super surface processing technology L min Determine the width of the design domain for a 2D cell structure L d = L - L min ; According to the design wavelength l 0Determine the structured grid size L mesh , and constrain L mesh ≤ l 0 / 8, in order to ensure the calculation accuracy of the complex amplitude transmittance of different two-dimensional unit structures according to the Helmholtz equation, and at the same time ensure L , Lmin Both L mesh An integer multiple of ; According to the refractive index of the dielectric material used in the metaaxon n Determine the thickness of the design domain of a 2D cell structure H , H The range is 1.5 l 0 / ( n -1) to 2 l 0 / ( n -1).

[0012] Furthermore, the cone angle of the 0th-order Bessel beam is set to i , for the ideal modulation phase of the design wavelength λ0 for: ; in, is the remainder function, P 0 is the phase constant, r is the radial coordinate of the phase modulation surface; For the position of the phase modulation surface with radial coordinate r, a two-dimensional unit structure with the best light modulation characteristics is selected from the unit structure library according to a set selection rule and placed there.

[0013] Furthermore, the formula for selecting the rule is as follows: ; in, E x , E z is the complex amplitude ratio of the two-dimensional unit structure to TM and TE waves, W TE and W TM is the weight of TE wave and TM wave, i Is an imaginary unit.

[0014] Furthermore, in step S2, each grid in the design domain of the two-dimensional unit structure is encoded by a binary string, 1 represents that the grid contains dielectric material, and 0 represents that the grid does not contain dielectric material; the binary strings corresponding to all two-dimensional unit structures are traversed, and when the continuation length of the same-value string of a certain two-dimensional unit structure is less than the minimum characteristic size of the supersurface processing technology L min , it is determined that the characteristic size of the two-dimensional unit structure is smaller than the minimum size allowed by the super-surface processing technology and does not meet the super-surface processing technology requirements. All two-dimensional unit structures that do not meet the super-surface processing technology requirements are screened out, and all two-dimensional unit structures that meet the super-surface processing technology requirements are retained and integrated into the unit structure library.

[0015] A metaaxon mirror, used for generating Bessel beams, is obtained by using the above-mentioned design method of the metaaxon mirror.

[0016] An imaging system comprises a camera and the above-mentioned meta-axon.

[0017] An imaging method, implemented using the above imaging system, comprises the following steps: S1: The object is imaged by an imaging system to obtain an original image; wherein the object passes through a meta-axon mirror to generate a Bessel beam, and an image is formed on the camera target surface; S2: Use a non-blind image restoration algorithm to process the original image to obtain an achromatic restored image.

[0018] Furthermore, after step S1 and before step S2, the following steps are also included: The intensity of the 0th order diffracted light is calculated according to the diffraction efficiency of the metaaxon and removed from the original image.

[0019] Furthermore, the imaging model of the hyperaxon is set as: ; in, The image is collected by the super-axis conic mirror; , is the transmission band of the super-axicon; The wavelength The point spread function of is the convolution symbol; It means that the object has a wavelength of incident light. The ideal image at this time; B is the intensity of the 0th order diffraction light of the super-axicon; make , then: ; Using the objective function x Make an estimate and get an estimated value : ; in, is the regularization coefficient, is a regularization term, corresponding to x The priors; Different priors adopt different non-blind image restoration algorithms.

[0020] Furthermore, when the L2 norm is used as the prior, the corresponding non-blind image restoration algorithm is the Wiener filter method; when the L1 norm of the gradient is used as the prior, the corresponding non-blind image restoration algorithm is the total variation method.

[0021] Furthermore, the estimated value is calculated based on the transmittance and diffraction efficiency of each transmission band of the meta-axon. Make corrections.

[0022] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention utilizes the wide spectrum consistency of the point spread function of the Bessel beam generated by the wide spectrum meta-axon lens, combined with a non-blind image restoration algorithm, to achieve chromatic aberration elimination to a great extent, and the clarity of the imaging result is greatly improved. Compared with the imaging of the point-focusing meta-lens based on a narrow-band design, it has obvious advantages in aperture, clarity and chromatic aberration suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1a A schematic diagram of the red, green and blue focusing of the point-focusing meta-lens described in the embodiment of the present invention and a schematic diagram of the corresponding point spread function; Figure 1b A schematic diagram of red, green and blue focusing of the superaxic mirror and a schematic diagram of the corresponding point spread function described in an embodiment of the present invention; Figure 2 A schematic flow chart of a design method of a metaaxon mirror according to an embodiment of the present invention; Figure 3 A schematic diagram of a light modulation characteristic simulation model of a two-dimensional unit structure according to an embodiment of the present invention; Figure 4 A schematic cross-sectional view of a metaaxon mirror according to an embodiment of the present invention; Figure 5 A schematic diagram of the three-dimensional structure of the superaxon mirror described in the embodiment of the present invention; Figure 6 A schematic diagram showing the relationship between the relative intensity and propagation distance z of Bessel beams of different wavelengths generated by the metaaxon described in an embodiment of the present invention; Figure 7 A schematic diagram of the wide-spectrum diffraction efficiency and relative intensity of the focal spot of the meta-axon mirror described in an embodiment of the present invention; Figure 8a A schematic diagram of a simulation target imaging result according to an embodiment of the present invention; Figure 8b A schematic diagram of the imaging result of a monochromatic meta-lens (design wavelength 600nm) with equal aperture and focal length as described in an embodiment of the present invention; Figure 8c A schematic diagram of direct imaging results of a super pyramid mirror according to an embodiment of the present invention; Figure 8d For the present invention to create the embodiment of the Figure 8c Schematic diagram of the imaging results after being processed by the image restoration algorithm. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0025] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0026] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0027] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0028] The image quality degradation problem caused by chromatic aberration when imaging point-focused meta-lenses is difficult to solve using image processing methods. If a meta-lens is prepared, a certain amount of imaging quality is sacrificed when imaging at a single wavelength, but for a fixed focal length , the point spread function of each wavelength The relative intensity distribution of is consistent, so that:

[0029] In formula (2), is the relative intensity coefficient of the point spread function, which is a constant at a given wavelength. Then equation (1) can be derived as:

[0030] After rearranging formula (3), we can obtain:

[0031] In formula (4), using the non-blind image restoration method, we can get , i.e. a clear band arrive Integral image. In the family of point spread functions that satisfy the requirements of formula (2), the present invention selects a Bessel beam generated by a meta-axon. The intensity distribution of the Bessel beam is as follows: E ( r , f , z )= A exp( I z z ) J n ( k r r ) exp(± inφ )(5); In formula (5), r , f , z is the three-dimensional cylindrical coordinate, the light beam propagates along the z direction, k r , k z for r Coordinates and z The wave vector components in the coordinates, A is a constant that is independent of coordinates, J n represent n For a Bessel beam without angular vortex, n = 0. The light intensity distribution of the 0th-order Bessel function is A 2 J 0 2 (2π / l r sin i ), i is the deflection angle of the incident light beam in the cross section of the meta-axon, which satisfies the grating equation in a wide spectral range.d sin i = l , d is the grating period of the equivalent grating in the cross section of the meta-axon. The intensity distribution of the Bessel beam can be simplified as A 2 J 0 2 (2π r / d ), its relative distribution is independent of wavelength, and it has excellent wide-spectrum consistency compared to the point-focusing meta-lens with severe wide-spectrum spot dispersion, such as Figure 1b Based on this characteristic, the present invention uses a super-axicon combined with a non-blind image restoration algorithm to achieve achromatic imaging of large-aperture metasurfaces, providing a new technical route for visible light full-color imaging with a single-chip metasurface as the core element.

[0032] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0033] like Figure 2 As shown, the present invention provides a design method of a meta-axon for generating a Bessel beam, comprising the following steps: S1: Construct a two-dimensional unit structure simulation model of a concentric ring structure, perform simulation calculations on the two-dimensional unit structure simulation model, and obtain the complex amplitude transmittance of the two-dimensional unit structure to incident light; wherein the cross-section of the concentric ring structure along the diameter forms two-dimensional unit structures of different configurations, and the two-dimensional unit structure is at the subwavelength level.

[0034] In the process of constructing the two-dimensional unit structure simulation model, according to the working parameters of the super-axon mirror (such as the design wavelength λ0, the beam deflection angle i , material refractive index n etc.), determine the structural dimensions of the two-dimensional unit structure simulation model.

[0035] After determining the structural dimensions of the two-dimensional unit structure simulation model, the finite element analysis method is used to establish a calculation model of the scattering field. The TE wave and TM wave are taken as the background field, and the complex amplitude transmittance of different two-dimensional unit structures is solved according to the Helmholtz equation.

[0036] According to the achromatic requirements of the imaging system composed of the meta-axon, the transmission band of the meta-axon is set to l l to l u , the design wavelength of the two-dimensional unit structure is set to l 0, l 0 2 = l l l u , to ensure that the natural dispersion law that satisfies the grating equation is achieved in the entire band.

[0037] According to the minimum operating wavelength l l Determining the cell width for a 2D cell structure simulation model L , and constrain L ≤ l l .

[0038] The super-axicon mirror includes a substrate and a concentric ring structure. The cross section of the concentric ring structure cut along the diameter is a two-dimensional unit structure. The two-dimensional unit structure is as follows: Figure 4 As shown, each rectangle represents a two-dimensional unit structure, that is, each rectangle represents a concentric ring structure. The light modulation characteristic simulation model of the two-dimensional unit structure is as follows Figure 3 As shown in the figure, the design domain refers to the object model used to represent the two-dimensional unit structure, the air perfect matching layer and the substrate perfect matching layer are a kind of simulation boundary conditions, and the air layer refers to a layer of air above the surface of the concentric ring structure in the electromagnetic field to be simulated. The design domain, perfect matching layer and air layer are commonly used concepts in the field of electromagnetic simulation.

[0039] Minimum processing size according to super surface processing technology L min Determine the width of the design domain for a 2D cell structure L d = L - L min .

[0040] According to the design wavelength l 0Determine the structured grid size L mesh , and constrain L mesh ≤ l 0 / 8, in order to ensure the calculation accuracy of the complex amplitude transmittance of different two-dimensional unit structures according to the Helmholtz equation, and at the same time ensure L , L min Both L mesh An integer multiple of .

[0041] According to the refractive index of the dielectric material used in the metaaxon n Determine the thickness of the design domain of a 2D cell structure H , H The range is 1.5 l 0 / (n -1) to 2 l 0 / ( n -1).

[0042] S2: According to the configuration of each two-dimensional unit structure and the limitations of the supersurface processing technology, the two-dimensional unit structure that meets the requirements of the supersurface processing technology is screened out and integrated into the unit structure library.

[0043] Each grid in the two-dimensional unit structure design domain is encoded by a binary string, 1 represents that the grid contains dielectric material, and 0 represents that the grid does not contain dielectric material.

[0044] Traverse the binary strings corresponding to all two-dimensional unit structures. When the continuation length of the same-value string of a two-dimensional unit structure (referring to the continuous characters 1 or 0) is less than the minimum characteristic size of the super surface processing technology, L min , it is determined that the characteristic size of the two-dimensional unit structure is smaller than the minimum size allowed by the supersurface processing technology and does not meet the supersurface processing technology requirements. All two-dimensional unit structures that do not meet the supersurface processing technology requirements are screened out, that is, all two-dimensional unit structures whose characteristic size is smaller than the minimum size allowed by the supersurface processing technology are screened out, and all two-dimensional unit structures that meet the supersurface processing technology requirements are retained and integrated into the unit structure library, thereby establishing a unit structure library containing complete optical information.

[0045] According to the cone angle of the required 0th order Bessel beam i , its ideal modulation phase for the design wavelength λ0 is:

[0046] in, is the remainder function, P 0 is a phase constant with an arbitrary value, and r is the radial coordinate of the phase modulation surface.

[0047] For the position of the radial coordinate r of the phase modulation surface, a two-dimensional unit structure with the best light modulation characteristics is selected from the unit structure library according to the set selection rule and placed there. The selection rule is to maximize the weighted sum of the projection values ​​of the complex amplitude transmittance of the TE and TM polarization modes of the two-dimensional unit structure to the corresponding target complex amplitude transmittance, as shown in the following formula: (7); in, E x , E z is the complex amplitude ratio of the two-dimensional unit structure to TM and TE waves, W TE and W TM is the weight of TE wave and TM wave, i Is an imaginary unit.

[0048] It should be noted that the amplitude transmittance vibrating along the direction of the two-dimensional unit structure is different from the amplitude transmittance vibrating in the direction perpendicular to the two-dimensional unit structure. In order to achieve focusing in two directions, compatibility of TE waves and TM waves is required. In order to achieve the best compatibility, the weights of TE waves and TM waves need to be adjusted so that the weighted sum of the projection values ​​of the target complex amplitude transmittance is maximized.

[0049] S3: Construct a two-dimensional cross-section of a metaaxon based on a concentric ring structure according to the two-dimensional unit structure in the unit structure library and the target phase plane, and rotate the two-dimensional cross-section around the optical axis of the metaaxon to obtain a three-dimensional structure of the metaaxon.

[0050] According to the target phase plane, all the two-dimensional unit structures are selected from the unit structure library to form a two-dimensional cross-sectional structure. The two-dimensional cross-sectional structure is rotated around the optical axis of the metaaxon to obtain the overall concentric ring structure, which is the overall three-dimensional structure of the metaaxon. Figure 5 shown.

[0051] In this embodiment, a normal incident plane wave with a working wavelength of 450nm to 700nm is subjected to a wave with a diameter of D =4mm silicon-based meta-lens design, design wavelength is l 0=532nm, the propagation length of the Bessel beam at this wavelength is L 0=30mm, the corresponding beam deflection angle is θ= atan(D / 2 / L 0)=3.8°, the distance from the focal plane to the meta-axon is defined as the focal length F =21mm. The specific parameters of the above-mentioned metaaxon are only a specific example, and the present invention does not specifically limit the design wavelength, aperture, Bessel beam propagation length, beam deflection angle, focal length and other parameters of the metaaxon.

[0052] In this embodiment, the Bessel beam propagation length of incident light of different wavelengths is approximately inversely proportional to the wavelength, wherein the Bessel beam length of incident light of wavelength 700nm is the smallest, so the focal length of the imaging system should be slightly smaller than the Bessel beam propagation length of incident light at the long-wave end, thereby ensuring that the focal plane can receive Bessel light spots in the full spectrum. In this embodiment, the focal length is selected as F =21mm.

[0053] like Figure 6 and Figure 7 As shown, in this embodiment, the diffraction efficiency of the meta-axon is obtained by Fourier analysis of the complex amplitude of near-field modulation in a single period. Figure 6is the peak relative intensity of Bessel beams of different wavelengths. The relative intensity of the spot in the focal plane is determined by the wide-spectrum diffraction efficiency and the propagation distance z. The intensity relationship is given by α λ .

[0054] The invention also provides an imaging system, including a camera and a meta-axon, wherein the camera is located in the emitting direction of the meta-axon, the meta-axon is used to generate a Bessel light beam, and the camera is used to image the Bessel light beam.

[0055] The present invention also provides an imaging method implemented by the imaging system, comprising the following steps: S1: The object is imaged by an imaging system to obtain an original image; wherein the object passes through a meta-axon mirror to generate a Bessel beam, and an image is formed on the camera target surface.

[0056] S2: Use a non-blind image restoration algorithm to process the original image to obtain an achromatic restored image.

[0057] Calibrate the point spread function of the meta-axon as the relative intensity coefficient of the broadband point spread function α λ The imaging results of the Bessel beam are processed based on the non-blind image restoration algorithm, and the relative intensity coefficient α λ The intensity of the 0th-order diffracted light is suppressed and white balance is processed to finally obtain a high-definition restored image with no chromatic aberration.

[0058] Due to the diffraction efficiency, most of the light beam is modulated into a Bessel beam, and a small part of the light beam is not modulated. Suppressing the intensity of the 0th order diffracted light is used to filter out the unmodulated light beam. White balance processing is used to adjust the color temperature deviation.

[0059] When taking an image, the focal length of the hyperaxon f is a constant value, so the f Omit and simplify to:

[0060] make , then:

[0061] When the intensity of the 0th order diffracted light is suppressed, the intensity of the 0th order diffracted light, that is, B in equation (8), is calculated according to the diffraction efficiency of the meta-axon and removed from the original image.

[0062] Use the following objective function to x Make an estimate and get an estimated value : (10); In formula (10), is the regularization term coefficient, which is a non-negative real number and can be adjusted according to the treatment effect; is a regularization term, corresponding to x The prior.

[0063] Different priors use different non-blind image restoration methods. For example, when the L2 norm is used as a prior, the corresponding non-blind image restoration algorithm is the Wiener filter method; when the L1 norm of the gradient is used as a prior, the corresponding non-blind image restoration algorithm is the total variation method.

[0064] When performing white balance processing, the estimated value is calculated based on the transmittance and diffraction efficiency of each transmission band of the super-axicon. Correction is performed, which is mainly aimed at using color sensors to collect images and correct the colors.

[0065] In this embodiment, a simulation verification based on the above-mentioned super-axicon and non-blind image restoration algorithm is provided, wherein the wavelength sampling range is 450nm to 700nm, and the sampling interval is 10nm. The image plane sampling range is within a square range with a side length of 0.4mm centered on the Bessel spot, and the sampling interval is 200nm. In this embodiment, the Bessel spot can maintain a high degree of spatial consistency within a 2° half field of view. Within this field of view, given an initial observed grayscale image such as Figure 8a shown.

[0066] If a meta-lens with the same specifications (aperture 4mm, focal length 21mm) is used for imaging, assuming that the 600nm band is focused, the blurred image caused by chromatic aberration is as follows: Figure 8b As shown, the peak signal-to-noise ratio (PSNR) of the image is 20.52dB at this time.

[0067] If the simulation-designed hyperaxonic mirror is used for imaging, the direct image obtained is as follows Figure 8c As shown, its PSNR is 21.81dB.

[0068] If the simulated designed hyperaxonic mirror is used for imaging, and the image is processed by the non-blind image restoration algorithm in the embodiment, the restored image obtained is as follows: Figure 8d As shown, its PSNR is 33.72dB, which is 13.2dB higher than that of traditional meta-lens, and the imaging resolution is significantly improved.

[0069] In terms of meta-lens structure design, the present invention constructs a simulation model of a two-dimensional structural unit, establishes a unit structure library, and constructs an overall structural section according to the unit structure library and the phase of the target meta-axon to obtain the overall three-dimensional structure of the meta-axon. In terms of imaging and image restoration, the initial image is obtained based on the wide spectrum consistency of the Bessel beam point spread function, and then a non-blind image restoration algorithm is used to process the image to obtain a chromatic aberration-free high-definition restored image.

[0070] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0071] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for designing a metaaxon, wherein the designed metaaxon is used to generate a Bessel beam, wherein: The steps include: S1: construct a two-dimensional unit structure simulation model of a concentric ring structure, perform simulation calculation on the two-dimensional unit structure simulation model, and obtain the complex amplitude transmittance of the two-dimensional unit structure to the incident light; wherein the cross section of the concentric ring structure along the diameter forms a two-dimensional unit structure of different configurations, and the two-dimensional unit structure is at the sub-wavelength level; S2: According to the configuration of each two-dimensional unit structure and the limitations of the supersurface processing technology, the two-dimensional unit structure that meets the requirements of the supersurface processing technology is screened and integrated into the unit structure library; S3: Construct a two-dimensional cross-section of a metaaxon based on a concentric ring structure according to the two-dimensional unit structure in the unit structure library and the target phase plane, and rotate the two-dimensional cross-section around the optical axis of the metaaxon to obtain a three-dimensional structure of the metaaxon.

2. The design method of the metaaxon according to claim 1, characterized in that: In step S1, the structural dimensions of the two-dimensional unit structure simulation model are determined according to the working parameters of the metaaxon.

3. The design method of the metaaxon according to claim 2, characterized in that: After determining the structural dimensions of the two-dimensional unit structure simulation model, the finite element analysis method is used to establish a calculation model of the scattering field. The TE wave and TM wave are taken as the background field, and the complex amplitude transmittance of different two-dimensional unit structures is solved according to the Helmholtz equation.

4. The design method of the metaaxon according to claim 3, characterized in that: Set the transmission band of the Metaaxon to λ l to λ u , and set the design wavelength of the two-dimensional unit structure to λ 0, λ 0 2 = λ l λ u ,but: According to the minimum operating wavelength λ l Determining the cell width for a 2D cell structure simulation model Λ , and constrain Λ ≤ λ l ; Minimum processing size according to super surface processing technology L min Determine the width of the design domain for a 2D cell structure L d = Λ - L min ; According to the design wavelength λ 0Determine the structured grid size L mesh , and constrain L mesh ≤ λ 0 / 8, in order to ensure the calculation accuracy of the complex amplitude transmittance of different two-dimensional unit structures according to the Helmholtz equation, and at the same time ensure Λ , L min Both L mesh An integer multiple of ; According to the refractive index of the dielectric material used in the metaaxon n Determine the thickness of the design domain of a 2D cell structure H , H The range is 1.5 λ 0 / ( n -1) to 2 λ 0 / ( n -1).

5. The design method of the metaaxon according to claim 4, characterized in that: Set the cone angle of the 0th-order Bessel beam to θ , for the ideal modulation phase of the design wavelength λ0 for: ； in, is the remainder function, Ψ 0 is the phase constant, r is the radial coordinate of the phase modulation surface; For the position of the phase modulation surface with radial coordinate r, a two-dimensional unit structure with the best light modulation characteristics is selected from the unit structure library according to a set selection rule and placed there.

6. The design method of the metaaxon according to claim 5, characterized in that: The formula for selecting the rule is as follows: ； in, E x , E z is the complex amplitude ratio of the two-dimensional unit structure to TM and TE waves, W TE and W TM is the weight of TE wave and TM wave, i Is an imaginary unit.

7. The design method of a metaaxon according to claim 4, characterized in that: In step S2, each grid in the design domain of the two-dimensional unit structure is encoded by a binary string, 1 represents that the grid contains dielectric material, and 0 represents that the grid does not contain dielectric material; the binary strings corresponding to all two-dimensional unit structures are traversed, and when the continuation length of the same-value string of a certain two-dimensional unit structure is less than the minimum characteristic size of the supersurface processing technology, L min , it is determined that the characteristic size of the two-dimensional unit structure is smaller than the minimum size allowed by the super-surface processing technology and does not meet the super-surface processing technology requirements. All two-dimensional unit structures that do not meet the super-surface processing technology requirements are screened out, and all two-dimensional unit structures that meet the super-surface processing technology requirements are retained and integrated into the unit structure library.

8. A meta-axon for generating Bessel beams, characterized in that: The method is obtained by using the design method of the metaaxon as described in any one of claims 1 to 7.

9. An imaging system comprising a camera, characterized in that: It also includes the meta-axon mirror as described in claim 8.

10. An imaging method, implemented using the imaging system according to claim 9, characterized in that: The steps include: S1: The object is imaged by an imaging system to obtain an original image; wherein the object passes through a meta-axon mirror to generate a Bessel beam, and an image is formed on the camera target surface; S2: Use a non-blind image restoration algorithm to process the original image to obtain an achromatic restored image.

11. The imaging method according to claim 10, characterized in that: After step S1 and before step S2, the method further includes the following steps: S110: Calculate the intensity of the 0th order diffraction light according to the diffraction efficiency of the meta-axon and remove it from the original image.

12. The imaging method according to claim 10, characterized in that: The imaging model of the hyperaxon is set as: ； in, The image is collected by the super-axis conic mirror; , is the transmission band of the super-axicon; The wavelength The point spread function of is the convolution symbol; It means that the object has a wavelength of incident light. The ideal image at this time; B is the intensity of the 0th order diffraction light of the super-axicon; make , then: ； Using the objective function x Make an estimate and get an estimated value : ； in, is the regularization coefficient, is a regularization term, corresponding to x The priors; Different priors adopt different non-blind image restoration algorithms.

13. The imaging method according to claim 12, characterized in that: When the L2 norm is used as the prior, the corresponding non-blind image restoration algorithm is the Wiener filtering method; when the L1 norm of the gradient is used as the prior, the corresponding non-blind image restoration algorithm is the total variation method.

14. The imaging method according to claim 12, characterized in that: According to the transmittance and diffraction efficiency of each transmission band of the super-axicon, the estimated value Make corrections.

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