Superlens-grating structure and design method thereof

Abstract

The present invention provides a superlens-grating structure and a design method thereof, wherein the superlens-grating structure is a superlens coupled with a one-dimensional grating, and the superlens and the one-dimensional grating are respectively processed on the front surface and the rear surface of a transparent substrate, thereby obtaining a superlens-grating structure with color separation and focusing functions. A light source emits a light beam incident on a collimator, which is collimated by the collimator to become a parallel light beam vertically incident on a superlens-grating structure; the superlens-grating structure includes a superlens and a one-dimensional grating; the superlens and the one-dimensional grating are respectively processed on the front surface and the rear surface of a substrate, thereby obtaining a superlens-grating structure with color separation and focusing functions; the parallel light beam is subjected to color separation and focusing of the superlens-grating structure, and a spectral distribution is obtained on a detector. By applying the superlens-grating structure provided by the present invention to a spectrometer device, the size and weight of the spectrometer system are reduced, and the spectral resolution is improved.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to a superlens-grating structure and its design method. Background Technology

[0002] Spectrometers are widely used and important spectral measurement instruments, applicable to fields such as material spectral analysis. Based on the principle of optical dispersion, a spectrometer disperses polychromatic light into monochromatic light of different wavelengths and measures the spectral intensity of each monochromatic light corresponding to its wavelength. Based on the measured spectral data and waveforms, it is possible to analyze the light composition, measure the optical properties of substances, and identify the components of gases. In recent years, ultra-compact spectrometers with high resolution and / or broadband characteristics have attracted widespread attention due to their broad application prospects.

[0003] As a novel planar optical instrument, the superlens' planar structure offers advantages such as simple manufacturing and low insertion loss. Furthermore, superlenses can achieve compact control over the spatial distribution of reflected and transmitted light fields. For example... Figure 1 As shown, in a traditional spectrometer, light passes through a collimating lens 01 and illuminates a diffraction grating 02. The diffraction grating 02 disperses the spectrum in different directions, and finally, a focusing lens 03 focuses the dispersed light onto a detector 04 to obtain the spectral distribution. The entire process involves a long transmission distance, requiring a relatively long propagation distance to achieve phase accumulation in order to fully separate different wavelengths and obtain high spectral resolution. This results in most spectrometers being quite bulky and having high energy consumption. Summary of the Invention

[0004] In view of the above problems, the purpose of this invention is to propose a superlens-grating structure and its design method.

[0005] The superlens-grating structure proposed in this invention integrates a superlens and a one-dimensional grating. A superlens is constructed on the front surface of the substrate, and a one-dimensional grating is constructed on the rear surface, thus creating a diffraction element with color separation and focusing functions, which is then applied in a spectrometer.

[0006] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0007] This invention provides a superlens-grating structure that couples a superlens and a one-dimensional grating. By processing the superlens and the one-dimensional grating on the front and back surfaces of a transparent substrate, a superlens-grating structure with color separation and focusing functions is obtained.

[0008] The superlens-grating structure is used in conjunction with a light source, collimating lens, and detector to obtain the spectral distribution; the process is as follows:

[0009] The light beam emitted by the light source is incident on the collimating lens, and after being collimated by the collimating lens, it becomes a parallel light beam that is incident perpendicularly on the superlens-grating structure.

[0010] After the parallel beam is separated and focused by the superlens-grating structure, its spectral distribution is obtained on the detector.

[0011] Preferably, the superlens is an off-axis superlens. An off-axis superlens is a truncated superlens that deviates from the center of an axisymmetric superlens, separating the axes of different wavelength beams and focusing them separately at different points off the original optical axis. The off-axis superlens is used to achieve focusing and color separation functions.

[0012] Superlenses achieve focusing at a specified location by controlling the phase distribution of nanounits;

[0013] One-dimensional gratings achieve beam splitting by modulating the amplitude or phase of a light beam.

[0014] This invention also provides a method for designing a superlens-grating structure, comprising the following steps:

[0015] S1. Establish the one-dimensional grating transmittance function and the superlens transmittance function respectively;

[0016] S2. Combine the superlens and the one-dimensional grating to obtain the superlens-grating structure, and calculate the complex amplitude transmittance function based on the transmittance functions of the superlens and the one-dimensional grating.

[0017] S3. Place the superlens-grating structure on the z=0 plane and illuminate it with a plane light wave to obtain a diffracted beam. Calculate the complex amplitude of the diffracted beam on any plane z>0 according to the complex amplitude transmittance function.

[0018] S4. The focusing position of the light source when the working wavelength is λ is obtained from the complex amplitude of the diffracted beam on any plane where z>0.

[0019] S5. The period of the nanopillar of the superlens and the period of the one-dimensional grating are allocated respectively to achieve the function of beam splitting and focusing.

[0020] Preferably, in step S1:

[0021] The transmittance function of a one-dimensional grating is:

[0022] h(x)=exp(i2πAx) (1)

[0023] Where h(x) is the transmittance distribution of a one-dimensional grating, x is the position coordinate of a one-dimensional grating, and A is the slope of the phase distribution of a one-dimensional grating.

[0024] Preferably, in step S1:

[0025] The establishment of the superlens transmittance function includes the following sub-steps:

[0026] S11. Establish the phase distribution function of the superlens:

[0027]

[0028] in,

[0029] Φ(x,y) is the phase distribution function of the superlens;

[0030] (x,y) represents the coordinates of any position in the plane where the superlens is located;

[0031] f is the focal length of the superlens.

[0032] x f y f , z f These are the focusing position coordinates of the superlens at the designed wavelength;

[0033] λ is the operating wavelength of the light source;

[0034] S12. The transmittance function of the superlens is calculated based on the phase distribution function of the superlens:

[0035]

[0036] in,

[0037] g(x,y) is the transmittance function of the superlens;

[0038] λ0 is the design wavelength for the superlens phase;

[0039] S13. Based on the dispersion and focusing characteristics of the superlens, we obtain... Therefore, formula (3) simplifies to:

[0040]

[0041] Combining formulas (3) and (4), the transmittance function of the superlens is obtained as follows:

[0042]

[0043] Preferably, in step S2:

[0044] The complex amplitude transmittance function is:

[0045] u(x,y)=h(x)g(x,y) (6)

[0046] Preferably, step S3 includes:

[0047] The complex amplitude of the diffracted beam in any plane z>0 is obtained by Fresnel integration as follows:

[0048]

[0049] in,

[0050] z represents any position on the z-axis in the space where the superlens-one-dimensional grating is located;

[0051] (x′,y′) represents the coordinate position on any cross section perpendicular to the z-axis in the propagation space where z>0.

[0052] Preferably, step S4 includes:

[0053] In y f =0, x′-z plane, the focusing position of the beam is obtained when the following conditions are met:

[0054]

[0055] Wherein, ΔΨ0 is the phase difference between adjacent gratings when the superlens is incident at wavelength λ0;

[0056] n(λ) is the refractive index of the medium when the incident wavelength is the working wavelength λ;

[0057] n(λ0) is the refractive index of the medium when the incident wavelength is the design wavelength λ0;

[0058] T is the period of the one-dimensional grating;

[0059] According to formula (8), the incident beam will be focused at (x) when passing through the superlens-grating structure. f +λ0 2 z f ΔΨ0n(λ) / (λ2πTn(λ0)),0,λ0z f At position / λ), the focusing position changes with the operating wavelength λ of the light source.

[0060] Preferably, step S5 includes:

[0061] Let the period of the nanopillar of the superlens be t1, and the period of the one-dimensional grating be t2;

[0062] To ensure that the one-dimensional grating does not produce a resonant response, the period of the one-dimensional grating is greater than the working wavelength λ; the structural parameters of the period of the superlens nanopillar and the period of the one-dimensional grating are t2=N×t1, where N is a positive integer greater than 1;

[0063] The center of the superlens unit coincides with the center of the fence of the one-dimensional grating, and the length of the one-dimensional grating in the y-direction coincides with the upper and lower edges of the entire nanopillar array of the superlens.

[0064] Preferably, the minimum spectral resolution of the superlens-grating structure is:

[0065]

[0066] In the formula, |Δr| represents the distance between different focusing positions when the working wavelength and the design wavelength are incident;

[0067] Δλ is the wavelength difference between the operating wavelength λ and the design wavelength λ0;

[0068] NA is the numerical aperture of the superlens-one-dimensional grating structure;

[0069] D is the diameter of the superlens-one-dimensional grating structure;

[0070] x′ is the x-coordinate of the focal position;

[0071] z f Let be the z-coordinate of the focusing position of the superlens at the design wavelength λ0;

[0072] ΔΨ0 is the phase difference between adjacent gratings when the design wavelength λ0 is incident;

[0073] β is the angle subtended by the focusing position at the design wavelength with respect to the superlens-one-dimensional grating structure;

[0074] n(λ) is the refractive index of the superlens-one-dimensional grating structure at the operating wavelength λ;

[0075] n(λ0) is the refractive index of the superlens-one-dimensional grating structure at the design wavelength λ0.

[0076] Compared with existing technologies, the present invention has the following advantages:

[0077] (1) Reduce the size and weight of the spectrometer system

[0078] This invention employs a superlens-grating structure with color-separation focusing function in the spectrometer to replace the traditional grating and focusing lens, avoiding the long transmission distance required for phase accumulation in traditional spectrometers, thereby reducing the system size and making the spectrometer lighter.

[0079] (2) High spectral resolution

[0080] This invention enables a spectrometer system with higher resolution than off-axis superlenses by adjusting parameters such as the focusing position, period of the superlens, and period of the one-dimensional grating. The spectral resolution can reach up to the pm level. Attached Figure Description

[0081] Figure 1 This is a schematic diagram of the optical path used in a traditional dispersive spectrometer to achieve light focusing and dispersion.

[0082] Figure 2 This is a schematic diagram of the optical path for focusing and splitting light using the superlens-grating structure provided by the present invention.

[0083] Figure 3 This is a flowchart illustrating the superlens-grating structure design method provided in an embodiment of the present invention.

[0084] Figure 4 This is a schematic diagram of the phase distribution of a one-dimensional grating in the superlens-grating structure according to the present invention.

[0085] Figure 5 This is a schematic diagram of the height distribution of a one-dimensional grating in the superlens-grating structure according to the present invention.

[0086] Figure 6 This is a light intensity curve diagram of light focusing and spectral dispersion provided according to an embodiment of the present invention.

[0087] Figure 7 The curves show a comparison of the spectral resolution of the superlens-grating structure and the off-axis superlens provided in the embodiments of the present invention.

[0088] The accompanying reference numerals include: collimating lens 1, superlens-grating structure 2, and detector 3. Detailed Implementation

[0089] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0090] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be 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 merely illustrative of the invention and do not constitute a limitation thereof.

[0091] Figure 2 This is a schematic diagram of the optical path for focusing and splitting light using a superlens-grating structure provided in an embodiment of the present invention.

[0092] like Figure 2 As shown, the superlens-grating structure for a spectrometer provided in this embodiment of the invention includes: a light source, a collimating lens 1, a superlens-grating structure 2, and a detector 3;

[0093] A light beam emitted from the light source is incident on collimating lens 1. After being collimated by collimating lens 1, the incident light becomes a parallel beam and is incident perpendicularly on the superlens-grating structure 2. The superlens-grating structure 2 has the functions of dispersive spectral splitting and focused spectrum. After the parallel beam is dichroically focused by the superlens-grating structure 2, the spectral distribution is obtained on the detector 3. This invention reduces the required size of the system.

[0094] The superlens is an off-axis superlens, which is a portion of an axisymmetric superlens that is off-center. It can separate the axes of beams of different wavelengths and focus them separately at different points on the original optical axis. Focusing at a specified position can be achieved by controlling the phase distribution of the nanounits.

[0095] The one-dimensional grating is a beam splitting element that achieves beam splitting by modulating the amplitude or phase of the beam.

[0096] This invention couples a superlens and a one-dimensional grating. By fabricating the superlens and the one-dimensional grating on the front and back surfaces of the same substrate, a beam-splitting phase is introduced on top of the beam-splitting and focusing achieved by the superlens, thereby improving the beam-splitting capability on top of the focusing capability and forming a diffractive optical device with high dispersion beam splitting and focusing.

[0097] The working process of the superlens-grating structure applied to the spectrometer is as follows: When the incident light shines on the off-axis superlens on the front surface of the substrate through the collimating lens, the phase distribution on it has a focusing effect and a certain color separation effect on the light. When the light passes through the template and then through the one-dimensional grating on the rear surface, the color separation effect of the grating on different wavelengths of light is further amplified. The superposition of the two effects can focus light of different wavelengths at different positions.

[0098] Figure 3 A flowchart illustrating the superlens-grating structure design method provided according to an embodiment of the present invention is shown.

[0099] like Figure 3 As shown, the superlens-grating structure design method provided in this embodiment of the invention includes the following steps:

[0100] S1. Establish the transmittance function of the one-dimensional grating and the transmittance function of the superlens, respectively.

[0101] The transmittance function of a one-dimensional grating is:

[0102] h(x)=exp(i2πAx) (10)

[0103] Where h(x) is the transmittance distribution of a one-dimensional grating, x is the position coordinate of a one-dimensional grating, and A is the slope of the phase distribution of a one-dimensional grating.

[0104] Figure 4 A schematic diagram of the phase distribution of a one-dimensional grating in the superlens-grating structure of the present invention is shown.

[0105] Figure 5 A schematic diagram of the height distribution of a one-dimensional grating in the superlens-grating structure of the present invention is shown.

[0106] like Figure 4-5 As shown, according to formula (10), the phase distribution function of a one-dimensional grating can be obtained as follows:

[0107] Ψ(x)=2πAx (11)

[0108] Wherein, Ψ(x) is the phase distribution of the one-dimensional grating, x is the position coordinate of the one-dimensional grating, and A is the slope of the phase distribution of the one-dimensional grating;

[0109] Since the phase function of a one-dimensional grating is linear, we can obtain:

[0110]

[0111] Where ΔΨ is the phase difference between adjacent one-dimensional gratings, and T is the period of the one-dimensional grating;

[0112] When the operating wavelength λ is incident, the phase difference between adjacent fences is ΔΨ:

[0113]

[0114] Where ΔΨ is the phase difference between adjacent gratings when the working wavelength λ is incident, ΔΨ0 is the phase difference between adjacent gratings when the design wavelength λ0 is incident, n(λ) is the refractive index of the medium when the incident wavelength is the working wavelength λ, n(λ0) is the refractive index of the medium when the incident wavelength is the design wavelength λ0, and Δh is the height difference between adjacent gratings.

[0115] Combining formulas (12) and (13), the phase distribution slope A of the one-dimensional grating can be obtained:

[0116]

[0117] Where ΔΨ0 is the phase difference between adjacent gratings when the incident wavelength λ0 is the design wavelength, n(λ) is the refractive index of the medium when the incident wavelength is the working wavelength λ, n(λ0) is the refractive index of the medium when the incident wavelength is the design wavelength λ0, and T is the one-dimensional grating period.

[0118] Establishing the transmittance function of a superlens includes the following sub-steps:

[0119] S11. Establish the phase distribution function of the superlens:

[0120]

[0121] Where Φ(x,y) is the phase distribution function of the superlens, and (x,y) are the coordinates of any position in the plane containing the superlens. f is the focal length of the superlens. x f ,y f ,z f λ represents the focusing position coordinates of the superlens at the designed wavelength, and λ is the operating wavelength of the light source.

[0122] S12. The transmittance function of the superlens is calculated based on the phase distribution function of the superlens:

[0123]

[0124] Where g(x,y) is the transmittance function of the superlens, Φ(x,y) is the phase distribution function of the superlens, and (x,y) are the coordinates of any position in the plane containing the superlens. λ0 is the design wavelength of the superlens phase, f is the focal length of the superlens, and x... f ,y f ,z f These are the focusing position coordinates of the superlens at the designed wavelength.

[0125] S13. Based on the dispersion and focusing characteristics of a superlens, we can obtain... Therefore, formula (16) can be simplified to the following:

[0126]

[0127] S2. After combining the superlens and the one-dimensional grating on the same substrate, the complex amplitude transmittance function is calculated as follows:

[0128] u(x,y)=h(x)g(x,y) (18)

[0129] S3. If the superlens-grating structure is placed on the z=0 plane and illuminated with plane light waves, the complex amplitude of the diffracted beam on any plane z>0 can be obtained by Fresnel integration as follows:

[0130]

[0131] Where z represents any position on the z-axis in the space where the structure is located; (x′, y′) represents the coordinate position on any cross section perpendicular to the z-axis in the propagation space where z>0; λ0 is the design wavelength of the superlens phase, and λ is the operating wavelength of the light source; (x, y) represents any position coordinate on the plane where the superlens is located; f is the focal length of the superlens, x f ,y f ,z f These are the focusing position coordinates of the superlens at the designed wavelength.

[0132] S4. The focusing position of the light source when the working wavelength is λ is obtained from the complex amplitude of the diffracted beam on any plane where z>0.

[0133] In y f =0, in the x′-z plane, the brightest point of the spectrum with wavelength λ appears when the following conditions are met:

[0134]

[0135] According to formula (20), the incident beam will be focused at (x) when passing through the superlens-grating structure. f +λ0z f A,0,λ0z f At position / λ), the focusing position changes with the operating wavelength λ of the light source. Therefore, the superlens-grating structure of this invention can focus light of different wavelengths at different positions.

[0136] S5. The period of the nanopillar of the superlens and the period of the one-dimensional grating are rationally allocated to achieve beam splitting and focusing functions, including:

[0137] Let the period of the nanopillars of the superlens be t1 and the period of the grating be t2. The method for setting the distribution of the nanopillars and grating structure of the superlens is as follows:

[0138] To ensure that the one-dimensional phase grating does not produce a resonant response, the period of the one-dimensional grating needs to be greater than the wavelength. Since the metasurface and the grating are on the front and back surfaces of the substrate, respectively, the preferred structural parameters for the period of the superlens nanopillars and the period of the one-dimensional grating are t2 = N × t1, where N is a positive integer greater than 1. This ensures that the center of the superlens unit coincides with the center of the grating fence, guaranteeing that the length of the one-dimensional grating in the y-direction coincides with the upper and lower edges of the entire nanopillar array of the superlens, which facilitates simulation and fabrication.

[0139] Figure 6 The simulated light intensity curves for light focusing and beam splitting provided in the embodiments of the present invention are shown.

[0140] like Figure 6 As shown, λ1 = 10 μm, λ2 = 9.5 μm, λ3 = 9 μm, λ4 = 8.5 μm, and λ5 = 8 μm. Specific parameters are: entrance pupil diameter D = 200 μm, phase design wavelength λ0 = 9 μm, and the z-coordinate of the focusing position of the superlens-grating structure at the design wavelength is z0. f =200μm, the structural parameters of the superlens nanopillar period and the one-dimensional grating period are t2=2×t1, and the x-coordinate of the focusing position of the superlens-grating structure at the designed wavelength is x f =346.

[0141] Furthermore, the method for calculating the minimum spectral resolution achievable by the superlens-grating structure is as follows:

[0142]

[0143] Where |Δr| is the distance between different focusing positions when the working wavelength λ and the design wavelength λ0 are incident, Δλ is the wavelength difference between the working wavelength λ and the design wavelength λ0, NA is the numerical aperture of the superlens-grating structure; λ0 is the phase design wavelength of the superlens; λ is the working wavelength, D is the diameter of the superlens-grating structure, x′ is the x-coordinate of the focusing position, and zf Let denot λ be the z-coordinate of the focusing position of the superlens at the design wavelength, ΔΨ0 be the phase difference between adjacent gratings when incident at the design wavelength λ0, and β be the angle subtended by the focusing position on the structure at the design wavelength λ0; n(λ) is the refractive index of the superlens-grating structure at the working wavelength λ, and n(λ0) is the refractive index of the superlens-grating structure at the design wavelength λ0.

[0144] Figure 7 The diagram shows a comparison curve of the spectral resolution of the superlens-grating structure and the off-axis superlens provided in the embodiments of the present invention.

[0145] like Figure 7 As shown, the specific parameters are: phase design wavelength λ0 = 1550nm, focal length f = 6.1mm, entrance pupil diameter D = 1cm, focusing angle α = arctan(x) f / z f The figure shows a resolution comparison curve between the superlens-grating structure and the off-axis superlens when the focusing angle (α) varies within the range of 1° to 80°. As can be seen from the figure, when the focusing angle is less than 38°, the spectral resolution of the superlens-grating structure provided in this embodiment of the invention is within 500 pm, which is superior to the spectral resolution of the off-axis superlens. It should be noted that the smaller the focusing angle, the smaller the loss of imaging illumination. Therefore, the embodiment provided by this invention can achieve a better spectral resolution than the off-axis superlens while ensuring imaging illumination.

[0146] Although 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 can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0147] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for designing a superlens-grating structure, characterized in that: The following steps are involved: S1, establishing a one-dimensional grating transmittance function and a superlens transmittance function respectively; S2, combining the superlens and the one-dimensional grating to obtain a superlens-grating structure, and calculating a complex amplitude transmittance function according to the transmittance functions of the superlens and the one-dimensional grating; S3, placing the superlens-grating structure on a plane z=0, and illuminating it with a plane light wave to obtain a diffracted light beam, and calculating the complex amplitude of the diffracted light beam on any plane z>0 according to the complex amplitude transmittance function; S4, obtaining the focal position when the working wavelength of the light source is λ according to the complex amplitude of the diffracted light beam on any plane where z>0; S5. Distribute the period of the superlens nanocolumn and the period of the one-dimensional grating respectively to realize the functions of splitting and focusing the light beam.

2. The method for designing a superlens-grating structure according to claim 1, characterized in that: In step S1: The one-dimensional grating transmittance function is: h(x)=exp(i2πAx) (1) Wherein, h(x) is the one-dimensional grating transmittance distribution, x is the one-dimensional grating position coordinate, and A is the one-dimensional grating phase distribution slope.

3. The method for designing a superlens-grating structure according to claim 2, characterized in that: In step S1: The establishment of the metalens transmittance function includes the following sub-steps: S11, establishing the phase distribution function of the metalens: in, Φ(x,y) is the phase distribution function of the metalens; (x, y) are the coordinates of any position on the plane where the metalens is located; f is the focal length of the metalens, f=sqrt(x f 2 +y f 2 +z f 2 ); x f ,y f , z f are respectively the focal position coordinates of the metalens at the design wavelength; λ is the operating wavelength of the light source; S12. Calculate the transmittance function of the metalens according to the phase distribution function of the metalens: in, g(x,y) is the transmittance function of the metalens; λ0 is the phase design wavelength of the superlens; S13, according to the dispersion and focusing characteristics of the metalens, obtain (xx f ) 2 +(yy f ) 2 < <z f 2 , so the formula (3) is simplified to: Combining the formulas (3) and (4), the transmittance function of the metalens is obtained as follows:

4. The method for designing a superlens-grating structure according to claim 3, characterized in that: In step S2: The complex amplitude transmittance function is: u(x,y)=h(x)g(x,y) (6).

5. The method for designing a superlens-grating structure according to claim 4, characterized in that: The step S3 comprises: The complex amplitude of the diffracted beam on any plane with z>0 is obtained by Fresnel integral: in, z is an arbitrary position on the z-axis of the space where the superlens-one-dimensional grating is located; (x′, y′) is the coordinate position on any cross section perpendicular to the z-axis in the propagation space where z>0.

6. The method for designing a superlens-grating structure according to claim 5, characterized in that: The step S4 comprises: In y f = 0, x′-z plane, the focusing position of the light beam is obtained when the following conditions are met: Wherein, ΔΨ0 is the phase difference between adjacent gratings when the design wavelength λ0 of the metalens is incident; n(λ) is the refractive index of the medium when the incident wavelength is the working wavelength λ; n(λ0) is the refractive index of the medium when the incident wavelength is the design wavelength λ0; T is the period of the one-dimensional grating; According to formula (8), the incident light beam will be focused at (x f +λ0 2 z f ΔΨ0n(λ) / (λ2πTn(λ0)),0,λ0z f / λ) position, the focusing position changes with the change of the working wavelength λ of the light source.

7. The method for designing a superlens-grating structure according to claim 6, characterized in that: The step S5 comprises: Assume that the nanocolumn period of the superlens is t1, and the one-dimensional grating period is t2; To ensure that the one-dimensional grating does not produce a resonant response, the one-dimensional grating period is greater than the operating wavelength λ; the structural parameters of the superlens nanocolumn period and the one-dimensional grating period are t2=N×t1, where N is a positive integer greater than 1; The center of the super lens unit coincides with the fence center of the one-dimensional grating, and the length of the one-dimensional grating in the y direction coincides with the upper and lower edges of the entire nanocolumn array of the super lens.

8. The method for designing a superlens-grating structure according to claim 7, characterized in that: Also includes: The minimum spectral resolution of the superlens-grating structure is: Wherein, |Δr| is the distance between the working wavelength λ and the design wavelength λ0 at different focusing positions when incident; Δλ is the wavelength difference between the working wavelength λ and the design wavelength λ0; NA is the numerical aperture of the superlens-one-dimensional grating structure; D is the diameter of the superlens-one-dimensional grating structure; x′ is the x-direction coordinate of the focus position; z f is the z-direction coordinate of the focusing position of the metalens at the design wavelength λ0; ΔΨ0 is the phase difference between adjacent gratings when the design wavelength λ0 is incident; β is the angle of the focusing position to the superlens-one-dimensional grating structure at the design wavelength; n(λ) is the refractive index of the superlens-one-dimensional grating structure at the working wavelength λ; n(λ0) is the refractive index of the superlens-one-dimensional grating structure at the design wavelength λ0.

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