Metaaxon and its design method, imaging system and imaging method composed of metaaxon

Abstract

The present invention belongs to the field of metalens technology, and specifically relates to a metaaxon and its design method, an imaging system composed of the metaaxon, and an imaging method. The design method includes: constructing a two-dimensional unit structure simulation model of a concentric ring structure, performing simulation calculations on the two-dimensional unit structure simulation model, and obtaining the complex amplitude transmittance of the two-dimensional unit structure to incident light; screening two-dimensional unit structures that meet the processing requirements based on the configuration of each two-dimensional unit structure and the limitations of the metasurface processing technology, and integrating them into a unit structure library; constructing a two-dimensional cross-section of a metaaxon based on a concentric ring structure based on the two-dimensional unit structure and the target phase plane in the unit structure library, and rotating the two-dimensional cross-section around the optical axis of the metaaxon to obtain a three-dimensional structure of the metaaxon. The present invention utilizes the wide spectrum consistency of the point spread function of the Bessel beam generated by the metaaxon, combined with a non-blind image restoration algorithm, to eliminate chromatic aberration and improve image clarity.

Description

Technical Field

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

[0002] Metalenses offer advantages such as lightness, simplified structure, low cost, and high degrees of freedom in light field manipulation. Their weight is negligible compared to traditional lenses, effectively reducing the overall weight of the product. This lightweight feature is crucial in mobile devices and aerospace applications, significantly reducing energy consumption and improving device portability. Traditional catadioptric optical systems typically require multiple mirrors to achieve the desired optical performance, while metalenses can integrate all functions onto one or two metasurfaces. This simplified structure not only reduces product complexity but also mitigates the larger size associated with excessive lens elements, making the device more compact. In terms of optical performance, through sophisticated subwavelength structural design, metalenses enable independent and free manipulation of key light field parameters such as amplitude, phase, and polarization, thereby integrating multiple light manipulation functions. Thanks to these advantages, metalens technology has garnered sustained attention from optical practitioners over the past decade and holds broad application prospects in consumer electronics, security monitoring, automotive electronics, optical communications, and AR / VR.

[0003] Although metalenses have excellent integration performance, the chromatic aberration problem they exhibit seriously restricts their further development and application. 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-limited imaging. Currently, the achromatic design of metalenses is mainly based on phase dispersion control engineering, that is, the design of metaatoms for optimal phase matching across a wide spectrum. In this method, there is a strict mutual constraint between the aperture, numerical aperture, and wavelength of the metalens, resulting in the aperture of the current finished device being generally only on the order of hundreds of wavelengths, which still cannot meet the needs of most applications. Although 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. At the same time, it also introduces new problems such as low focusing efficiency and difficulty in micro-nanostructure processing.

[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]

[0006] in, is the focal length of the metalens, is the image collected by the meta-lens; [ , ] is the transmission band of the meta-lens; 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.

[0007] 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 quantities of this problem are far less than the unknown quantities, so it cannot be solved. For a 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

[0008] 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 metalenses with an aperture of the order of thousands of wavelengths or more are difficult to achieve continuous spectrum achromatic imaging.

[0009] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0010] A method for designing a metaaxon, wherein the designed metaaxon is used to generate a Bessel beam, comprises the following steps:

[0011] 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 a two-dimensional unit structure of different configurations, and the two-dimensional unit structure is at the subwavelength level;

[0012] S2: Based on the configuration of each two-dimensional unit structure and the limitations of the metasurface processing technology, the two-dimensional unit structures that meet the requirements of the metasurface processing technology are screened and integrated into the unit structure library;

[0013] 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.

[0014] 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.

[0015] Furthermore, after determining the structural dimensions of the two-dimensional unit structure simulation model, the finite element analysis method was used to establish a calculation model of the scattering field. The TE wave and TM wave normal incidence were used as the background field, and the complex amplitude transmittance of different two-dimensional unit structures was solved according to the Helmholtz equation.

[0016] Furthermore, the transmission band of the metaaxon is set to l l to l u , set the design wavelength of the two-dimensional unit structure to l 0, l 0 2 = l l l u ,but:

[0017] According to the minimum operating wavelength l l Determine the cell width for a 2D cell structure simulation model L , and constrain L ≤ l l ;

[0018] According to the minimum processing size of the super surface processing technology L min Determine the width of the design domain for a 2D unit structure L d = L - L min ;

[0019] According to the design wavelength l 0Determine the structured grid size L mesh , and constrain L mesh ≤ l0 / 8, in order to ensure the calculation accuracy of the complex amplitude transmittance of different two-dimensional unit structures according to the Helmholtz equation, while ensuring L 、 L min Both L mesh an integer multiple of ;

[0020] According to the refractive index of the dielectric material used in the metaaxon n Determine the thickness of the design domain of a 2D element structure H , H The range is 1.5 l 0 / ( n -1) to 2 l 0 / ( n -1).

[0021] 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:

[0022] ;

[0023] in, is the remainder function, P 0 is the phase constant, r is the radial coordinate of the phase modulation surface;

[0024] For the position with radial coordinate r on the phase modulation surface, a two-dimensional unit structure with optimal light modulation characteristics is selected from the unit structure library according to a set selection rule and placed there.

[0025] Furthermore, the formula for selecting the rule is as follows:

[0026] ;

[0027] in, E x 、 E z is the complex amplitude ratio of the two-dimensional unit structure to TM wave and TE wave, W TE and W TM is the weight of TE wave and TM wave, i Is an imaginary unit.

[0028] 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 two-dimensional unit structure is less than the minimum characteristic size of the metasurface 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.

[0029] A metaaxon is provided for generating Bessel beams and is obtained by adopting the above-mentioned design method of the metaaxon.

[0030] An imaging system comprises a camera and the above-mentioned metaaxon.

[0031] An imaging method, implemented using the above imaging system, comprises the following steps:

[0032] S1: The object is imaged by the imaging system to obtain the original image. The object passes through the meta-axon to generate a Bessel beam, which is then imaged on the camera target surface.

[0033] S2: Use a non-blind image restoration algorithm to process the original image to obtain an achromatic restored image.

[0034] Furthermore, after step S1 and before step S2, the following steps are further included:

[0035] The intensity of the 0th-order diffracted light is calculated based on the diffraction efficiency of the metaaxon and removed from the original image.

[0036] Furthermore, the imaging model of the meta-axon is set as:

[0037] ;

[0038] in, is the image collected by the meta-axonoscope; 、 is the transmission band of the meta-axon; wavelength The point spread function of is the convolution symbol; Indicates that the object is The ideal image when ; B is the intensity of the 0th order diffraction light of the meta-axon;

[0039] make , then:

[0040] ;

[0041] Using the objective function to x Make an estimate and get an estimated value :

[0042] ;

[0043] in, is the regularization coefficient, is a regularization term, corresponding to x Priors;

[0044] Different priors adopt different non-blind image restoration algorithms.

[0045] 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.

[0046] Furthermore, the estimated value is obtained based on the transmittance and diffraction efficiency of each transmission band of the meta-axon. Make corrections.

[0047] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0048] This invention leverages the broad spectral consistency of the point spread function (PSF) of the Bessel beam generated by a wide-spectrum metaaxon, combined with a non-blind image restoration algorithm, to significantly eliminate chromatic aberration and significantly improve imaging clarity. Compared to imaging using narrow-band, point-focusing metalenses, this approach offers significant advantages in aperture, clarity, and chromatic aberration suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1a A schematic diagram of the red, green, and blue color focusing of the point-focusing meta-lens described in an embodiment of the present invention and a schematic diagram of the corresponding point spread function;

[0050] Figure 1b Schematic diagram of red, green and blue color focusing and corresponding point spread function of the metaaxon described in an embodiment of the present invention;

[0051] Figure 2 A schematic flow chart of a design method for a metaaxon mirror according to an embodiment of the present invention;

[0052] 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;

[0053] Figure 4 A schematic cross-sectional view of a metaaxon mirror according to an embodiment of the present invention;

[0054] Figure 5 A schematic diagram of the three-dimensional structure of the metaaxon described in an embodiment of the present invention;

[0055] Figure 6Schematic diagram showing the relationship between the relative intensity and propagation distance z of Bessel beams of different wavelengths generated by the metaaxon according to an embodiment of the present invention;

[0056] Figure 7 Schematic diagram of the wide-spectrum diffraction efficiency and relative intensity of the focal spot of the metaaxon described in an embodiment of the present invention;

[0057] Figure 8a A schematic diagram of the simulated target imaging result according to an embodiment of the present invention;

[0058] Figure 8b Schematic diagram of imaging results using a monochromatic meta-lens (design wavelength 600nm) of equal aperture and focal length as described in an embodiment of the present invention;

[0059] Figure 8c A schematic diagram of direct imaging results of a meta-pyramid according to an embodiment of the present invention;

[0060] Figure 8d For the present invention to create the embodiment of the Figure 8c Schematic diagram of the imaging results after the imaging results are processed by the image restoration algorithm. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0062] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0063] 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 orientations or positional relationships based on the orientations 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" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like 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.

[0064] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0065] It is difficult to use image processing methods to solve the problem of image quality degradation caused by chromatic aberration when imaging point-focusing meta-lens. 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 remains consistent, so that:

[0066]

[0067] In formula (2), is the relative intensity coefficient of the point spread function, which is a constant at a given wavelength. Then formula (1) can be derived as:

[0068]

[0069] After sorting out formula (3), we can get:

[0070]

[0071] In formula (4), we can obtain , that is, a clear band arrive Integral image. Among the point spread function family that satisfies the requirements of formula (2), the present invention selects the Bessel beam generated by the metaaxon. The intensity distribution of the Bessel beam is as follows:

[0072] E ( r , f , z )= A exp( I z z ) J n ( k r r ) exp(± inφ )(5);

[0073] In formula (5), r 、 f 、 z is a 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 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. Based on this, the intensity distribution of the Bessel beam can be simplified to A 2 J 0 2 (2π r / d ), its relative distribution is independent of wavelength and 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 meta-axon combined with a non-blind image restoration algorithm to achieve achromatic imaging of large-aperture metasurfaces, providing a new technical solution for visible light full-color imaging with a single-chip metasurface as the core element.

[0074] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0075] like Figure 2 As shown, the present invention provides a method for designing a metaaxon for generating a Bessel beam, comprising the following steps:

[0076] 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 the incident light; wherein, the concentric ring structure forms two-dimensional unit structures of different configurations along the cross section of the diameter, and the two-dimensional unit structure is at the subwavelength level.

[0077] In the process of constructing the two-dimensional unit structure simulation model, according to the working parameters of the meta-axon (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.

[0078] After determining the structural dimensions of the two-dimensional unit structure simulation model, the finite element analysis method was used to establish a calculation model of the scattering field. The TE wave and TM wave normal incidence were used as the background field, and the complex amplitude transmittance of different two-dimensional unit structures was solved according to the Helmholtz equation.

[0079] According to the achromatic requirements of the imaging system composed of the meta-axicon, the transmission band of the meta-axicon 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 of the grating equation is satisfied in the entire band.

[0080] According to the minimum operating wavelength l l Determine the cell width for a 2D cell structure simulation model L , and constrain L ≤ l l .

[0081] The meta-axon 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 perfectly matched layer and the substrate perfectly matched layer are simulation boundary conditions. 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, perfectly matched layer and air layer are commonly used concepts in the field of electromagnetic simulation.

[0082] According to the minimum processing size of the super surface processing technology L min Determine the width of the design domain for a 2D unit structure L d = L - L min .

[0083] 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, while ensuring L 、 L min Both L mesh An integer multiple of .

[0084] According to the refractive index of the dielectric material used in the metaaxon n Determine the thickness of the design domain of a 2D element structure H , H The range is 1.5 l 0 / ( n -1) to 2 l 0 / ( n -1).

[0085] S2: Based on the configuration of each two-dimensional unit structure and the limitations of the metasurface processing technology, the two-dimensional unit structures that meet the requirements of the metasurface processing technology are screened out and integrated into the unit structure library.

[0086] Each grid in the two-dimensional unit structure design domain is encoded by a binary string, where 1 represents that the grid contains dielectric material, and 0 represents that the grid does not contain dielectric material.

[0087] 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 continuous characters 1 or 0) is less than the minimum feature size of the metasurface 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 requirements of the super-surface processing technology. All two-dimensional unit structures that do not meet the requirements of the super-surface processing technology are screened out, that is, all two-dimensional unit structures with characteristic sizes smaller than the minimum size allowed by the super-surface processing technology are screened out, and all two-dimensional unit structures that meet the requirements of the super-surface processing technology are retained and integrated into the unit structure library, thereby establishing a unit structure library containing complete optical information.

[0088] According to the cone angle of the required 0th order Bessel beam i , its ideal modulation phase for the design wavelength λ0 is:

[0089]

[0090] 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.

[0091] At the position with radial coordinate r on the phase modulation surface, a two-dimensional unit structure with optimal 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 two-dimensional unit structure in the TE and TM polarization modes on the corresponding target complex amplitude transmittance, as shown in the following formula:

[0092] (7);

[0093] in, E x 、 E z is the complex amplitude ratio of the two-dimensional unit structure to TM wave and TE wave, W TE and W TM is the weight of TE wave and TM wave, i Is an imaginary unit.

[0094] 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.

[0095] 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.

[0096] 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, as shown in Figure 2. Figure 5 shown.

[0097] 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, the 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. 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.

[0098] 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 with a wavelength of 700nm is the smallest. Therefore, the focal length of the imaging system should be slightly smaller than the Bessel beam propagation length of the incident light at the long wavelength end, so as to ensure that the focal plane can receive the Bessel light spot in the full spectrum. In this embodiment, the focal length is selected as F =21mm.

[0099] like Figure 6 and Figure 7 As shown in this embodiment, the diffraction efficiency of the metaaxon is obtained by Fourier analysis of the complex amplitude of the near-field modulation within a single period. Figure 6 The relative intensity of the Bessel beams at different wavelengths is the peak intensity. 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 the same as in Equation (2): α λ .

[0100] An embodiment of the present invention also provides an imaging system, including a camera and a metaaxon, wherein the camera is located in the emitting direction of the metaaxon, the metaaxon is used to generate a Bessel beam, and the camera is used to image the Bessel beam.

[0101] The present invention also provides an imaging method implemented using the above imaging system, comprising the following steps:

[0102] S1: The object is imaged by the imaging system to obtain the original image; wherein, the object passes through the meta-axon to generate a Bessel beam, and the image is formed on the camera target surface.

[0103] S2: Use a non-blind image restoration algorithm to process the original image to obtain an achromatic restored image.

[0104] Calibrate the point spread function of the metaaxon 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 processing is performed to finally obtain a high-definition restored image without chromatic aberration.

[0105] Due to diffraction efficiency, most of the light beam is modulated into a Bessel beam, while 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.

[0106] Since the focal length of the meta-axon is f is a constant value, so the formula (4) f Omit and simplify to:

[0107]

[0108] make , then:

[0109]

[0110] When suppressing the intensity of the 0th-order diffracted light, the intensity of the 0th-order diffracted light, that is, B in formula (8), is calculated according to the diffraction efficiency of the metaaxon and removed from the original image.

[0111] Use the following objective function to x Make an estimate and get an estimated value :

[0112] (10);

[0113] 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 prior.

[0114] Different priors lead to 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.

[0115] When performing white balance processing, the estimated value is calculated based on the transmittance and diffraction efficiency of each transmission band of the super-axon. Correction is performed, which is mainly aimed at using color sensors to collect images and correct the colors.

[0116] In this embodiment, a simulation verification based on the above-mentioned meta-axon 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 and a sampling interval of 200nm, centered on the Bessel spot. 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.

[0117] If a meta-lens with the same specifications (aperture 4mm, focal length 21mm) is used to image, assuming that the 600nm band is focused, the blurred image caused by chromatic aberration is as follows: Figure 8b As shown in Figure 2, the peak signal-to-noise ratio (PSNR) of the image is 20.52dB at this time.

[0118] If the simulation-designed meta-axon is used for imaging, the direct image obtained is as follows: Figure 8c As shown, its PSNR is 21.81dB.

[0119] If the simulated designed meta-axon 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 in the figure, its PSNR is 33.72dB, which is 13.2dB higher than that of traditional meta-lens, and the imaging resolution is significantly improved.

[0120] In the design of the metalens structure, this invention constructs a simulation model of two-dimensional structural units, establishes a unit structure library, and constructs an overall structural cross-section based on the unit structure library and the phase of the target metaaxon, thereby obtaining the overall three-dimensional structure of the metaaxon. In terms of imaging and image restoration, an initial image is obtained based on the wide-spectrum consistency of the Bessel beam point spread function. Subsequently, a non-blind image restoration algorithm is used for image processing to obtain a chromatically aberrated, high-definition restored image.

[0121] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art may make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0122] The above specific embodiments of the present invention do not constitute a limitation on the scope of protection 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 scope of protection of the claims of the present invention.

Claims

1. An imaging method is implemented using an imaging system, the imaging system comprising a camera and a metaaxon, the camera being located in the emission direction of the metaaxon, the metaaxon being used to generate a Bessel beam, and the camera being used to image the Bessel beam. The design method of the metaaxon comprises: A two-dimensional unit structure simulation model of a concentric ring structure is constructed, and simulation calculations are performed on the two-dimensional unit structure simulation model to 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 a two-dimensional unit structure of different configurations, and the two-dimensional unit structure is at the subwavelength level; According to the configuration of each two-dimensional unit structure and the limitations of the metasurface processing technology, the two-dimensional unit structures that meet the requirements of the metasurface processing technology are screened and integrated into the unit structure library; A two-dimensional cross-section of a metaaxon based on a concentric ring structure is constructed according to the two-dimensional unit structure in the unit structure library and the target phase plane. The two-dimensional cross-section is rotated around the optical axis of the metaaxon to obtain a three-dimensional structure of the metaaxon. The imaging method comprises the following steps: S1: The object is imaged by the imaging system to obtain the original image. The object passes through the meta-axon to generate a Bessel beam, which is then imaged on the camera target surface. S2: Use a non-blind image restoration algorithm to process the original image to obtain an achromatic restored image.

2. The imaging method according to claim 1, wherein After step S1 and before step S2, the following steps are further included: S110: Calculate the intensity of the 0th-order diffracted light according to the diffraction efficiency of the metaaxon and remove it from the original image.

3. The imaging method according to claim 1, wherein The imaging model of the meta-axon is set as: ； in, is the image collected by the meta-axonoscope; 、 is the transmission band of the meta-axon; wavelength The point spread function of is the convolution symbol; Indicates that the object is The ideal image when ; B is the intensity of the 0th order diffraction light of the meta-axon; make , then: ； Using the objective function to x Make an estimate and get an estimated value : ； in, is the regularization coefficient, is a regularization term, corresponding to x Priors; Different priors adopt different non-blind image restoration algorithms.

4. The imaging method according to claim 3, wherein: 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.

5. The imaging method according to claim 3, wherein: Estimated values ​​based on the transmittance and diffraction efficiency of each transmission band of the meta-axon Make corrections.

6. The imaging method according to claim 1, wherein: According to the working parameters of the meta-axon mirror, the structural dimensions of the two-dimensional unit structure simulation model are determined.

7. The imaging method according to claim 6, characterized in that After determining the structural dimensions of the two-dimensional unit structure simulation model, the finite element analysis method was used to establish a calculation model of the scattering field. The TE wave and TM wave normal incidence were used as the background field, and the complex amplitude transmittance of different two-dimensional unit structures was solved according to the Helmholtz equation.

8. The imaging method according to claim 7, wherein: Set the transmission band of the metaaxon to λ l to λ u , 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 Determine the cell width for a 2D cell structure simulation model Λ , and constrain Λ ≤ λ l ; According to the minimum processing size of the super surface processing technology L min Determine the width of the design domain for a 2D unit 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, while ensuring 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 element structure H , H The range is 1.5 λ 0 / ( n -1) to 2 λ 0 / ( n -1).

9. The imaging method according to claim 8, 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 with radial coordinate r on the phase modulation surface, a two-dimensional unit structure with optimal light modulation characteristics is selected from the unit structure library according to a set selection rule and placed there.

10. The imaging method according to claim 9, 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 wave and TE wave, W TE and W TM is the weight of TE wave and TM wave, i Is an imaginary unit.

11. The imaging method according to claim 8, wherein 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; the binary strings corresponding to all two-dimensional unit structures are traversed, and when the continuation length of the same value string of a two-dimensional unit structure is less than the minimum feature size of the metasurface 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.

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