A superlens based on a double-coupling structure

Abstract

The present invention proposes a metalens based on a dual-coupling structure, which relates to the field of optical zoom. The metalens comprises a substrate and a phase wavefront disposed on the substrate. The phase wavefront is composed of a plurality of periodically arranged nanopillars. A corresponding phase distribution value is assigned according to the position of each nanopillar to convert a plane wave incident on the phase wavefront into a light beam focused at a specified focal length. Each nanopillar has the same rectangular cross-section and is provided with a slit along its long axis. The slit passes through the nanopillar and extends to the surface of the substrate, so that the nanopillars form a dual-coupling structure. The present invention helps improve the focusing efficiency of the metalens.

Description

Technical Field

[0001] The present invention relates to the field of optical zoom, and in particular to a metalens based on a double-coupling structure. Background Art

[0002] Traditional lenses utilize the refractive index of a material and the phase accumulation of electromagnetic waves during their propagation to achieve beam control. However, these lenses suffer from significant drawbacks, such as bulk and difficulty integrating. Planar metalenses are imaging lenses composed of subwavelength elements that independently control the phase of the incident electromagnetic wave to achieve focusing. Compared to traditional lenses, planar metalenses offer small size, low cost, and ease of integration.

[0003] The Chinese patent with publication number CN116165731A discloses an intensity-tunable infrared band planar metalens and its adjustment method, which includes a top layer, a reflective layer and a substrate. The top layer is composed of a cylindrical unit array with a symmetrical number of left and right units, and the radius r of the multiple cylindrical units decreases from the center to both sides. The reflective layer is composed of a phase change material VO2, and the substrate is composed of a dielectric. Although the above scheme forms a metalens by forming a cylindrical unit array with decreasing radius to achieve continuous adjustment of the focus intensity, the light waves transmitted from the substrate will still oscillate in the reflective layer or be absorbed / lost in the reflective layer. Therefore, it is very necessary to provide a metalens based on a dual-coupling structure to improve the focusing efficiency of the metalens. Summary of the Invention

[0004] In light of this, the present invention proposes a metalens based on a dual-coupling structure. By forming a dual-coupling structure through slits in the nanopillars, light waves transmitted from the substrate are tightly confined within the coupling structure, greatly improving focusing efficiency and increasing the focal energy of the metalens.

[0005] The present invention provides a metalens based on a dual-coupling structure, comprising a substrate and a phase wavefront arranged on the substrate, wherein the phase wavefront is composed of a plurality of periodically arranged nanopillars. A corresponding phase distribution value is assigned according to the position of each nanopillar to convert a plane wave incident on the phase wavefront into a light beam focused at a specified focal length, wherein each nanopillar has the same rectangular cross-section and a slit is provided in the long axis direction of the nanopillar, wherein the slit passes through the nanopillar and extends to the surface of the substrate, so that the nanopillars form a dual-coupling structure.

[0006] On the basis of the above technical solution, preferably, the expression of the phase distribution value is:

[0007]

[0008] in, represents the lower phase distribution value with coordinates (x, y), f represents the specified focal length of the phase wavefront, λ is the wavelength, x represents the abscissa of the center position of the nanopillar when placed on the substrate, and y represents the ordinate of the center position of the nanopillar when placed on the substrate.

[0009] On the basis of the above technical solution, preferably, the length of the nanocolumn is 390nm-410nm, the width of the nanocolumn is 207nm-217nm, the height of the nanocolumn is 890nm-910nm, and the width of the slit is 20nm-24nm.

[0010] More preferably, the straight-line distance between the geometric center points of any two adjacent nanocolumns is 500 nm.

[0011] More preferably, the numerical aperture of the metalens is 0.28 to 0.82, and the operating wavelength range of the metalens is 440 nm to 670 nm.

[0012] More preferably, when the numerical aperture of the metalens is 0.44 to 0.6, the focal spot of the metalens has a Gaussian distribution, and the full width at half maximum of the focal spot meets the diffraction limit.

[0013] More preferably, the nanorods are periodically arranged on the substrate in a close-packed square or a close-packed circular pattern.

[0014] More preferably, the focal length of the superlens is adjusted by changing the phase distribution of the nanorods, and the focal length of the superlens is 10 μm to 50 μm.

[0015] More preferably, the thickness of the substrate is 290 nm to 310 nm.

[0016] More preferably, the material of the substrate is SiO2, and the material of the nanorods is TiO2.

[0017] The metalens based on the dual-coupling structure provided by the present invention has the following beneficial effects compared with the prior art:

[0018] (1) A double-coupling structure is formed by the through-slit in the nanocolumn, which produces a strong local enhancement effect of the electromagnetic field, significantly improves the phase control range, and can achieve full phase coverage of 0-2π. At the same time, the double-coupling structure enhances the interaction between light and the nanostructure. The through-slit design reduces the reflection loss of light, and the light waves transmitted from the substrate will be tightly confined in the coupling structure without oscillating in the coupling structure or being absorbed / lost in the waveguide, which greatly improves the focusing efficiency and the focal spot energy of the superlens. In addition, the working bandwidth is significantly broadened to cover the visible light to near-infrared band, reducing the polarization dependence, and having a good control effect on light of different polarization states. While maintaining excellent optical performance, the uniform rectangular cross-section design and periodic arrangement characteristics make the device have good process compatibility and mass production capabilities.

[0019] (2) The superlens uses a material combination of SiO2 substrate and TiO2 nanopillars, making full use of the excellent optical properties and processing compatibility of the two materials. At the same time, the precise size design of the nanopillars matches the wavelength of visible light. Combined with the optimized slit width and substrate thickness, an efficient optical control structure is formed. The strict tolerance control of various parameters ensures the stability and consistency of device performance and maintains good process feasibility. This structural design not only achieves excellent optical performance, but also has good mechanical stability and reliability. (3) The superlens achieves coverage of a wide operating wavelength range and a large numerical aperture range. In particular, in the optimal operating range of numerical aperture 0.44-0.6, a diffraction-limited Gaussian distribution focal spot can be obtained, ensuring high resolution and high quality of imaging. At the same time, the focal length of the superlens can be continuously adjusted in the range of 10μm to 50μm by adjusting the phase distribution of the nanopillars, providing a 5-fold adjustment range, which makes the superlens have excellent imaging quality, good adjustability and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A schematic structural diagram of the dual coupling structure provided by the present invention;

[0022] Figure 2 This is the electric field distribution diagram after the left-handed circularly polarized light provided by the present invention is incident;

[0023] Figure 3 Schematic diagram of the phase rotation angle distribution of the LCP under the incident monochromatic light provided by the present invention;

[0024] Figure 4 A simulation diagram for verifying the metalens provided by the present invention in the visible spectrum;

[0025] Figure 5 A comparison diagram of the focal position and focal spot energy of the metalens provided by the present invention;

[0026] Figure 6 Schematic diagram of the FWHM focal plane peak of the metalens provided by the present invention;

[0027] Figure 7 Statistical diagram of focusing conditions at four different numerical apertures in the visible spectrum provided by the present invention;

[0028] Figure 8 The focal spot energy wavelength diagram under four different numerical apertures provided by the present invention;

[0029] Figure 9 This is a statistical diagram of normalized focusing efficiency and wavelength under different initial numerical aperture conditions provided by the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Before introducing the embodiments of the present invention, some terms and their abbreviations involved in the embodiments of the present invention are first defined and explained.

[0032] A metasurface is a precision optical modulation device composed of specially arranged optical micro-nanostructures with sub-wavelength geometric dimensions.

[0033] PB phase control (also known as geometric phase control) is a classic control method for metasurfaces. It introduces geometric phase changes of light simply by changing the rotation angle of the central axis of the nanostructure. Therefore, the most basic focusing function of the metalens can be achieved in the simplest way.

[0034] like Figure 1As shown, the present invention provides a metalens based on a dual-coupling structure, including a substrate and a phase wavefront arranged on the substrate, wherein the phase wavefront is composed of a plurality of periodically arranged nanopillars, and a corresponding phase distribution value is assigned according to the position point of each nanopillar to convert the plane wave incident on the phase wavefront into a light beam focused at a specified focal length, wherein each nanopillar has the same rectangular cross-section, and a slit is provided in the long axis direction of the nanopillar, the slit passes through the nanopillar and extends to the surface of the substrate, so that the nanopillars form a dual-coupling structure.

[0035] In this embodiment, the nanorods are periodically arranged on the substrate in a square close arrangement or a circular close arrangement, and the straight-line distance between the geometric center points of any two adjacent nanorods is 500 nm.

[0036] The expression of the phase distribution value is:

[0037]

[0038] in, represents the lower phase distribution value with coordinates (x, y), f represents the specified focal length of the phase wavefront, λ is the wavelength, x represents the abscissa of the center position of the nanopillar when it is placed on the substrate, and y represents the ordinate of the center position of the nanopillar when it is placed on the substrate.

[0039] The expression of the phase distribution value can determine the expected phase of each coordinate point (x,y). 2 +y 2 =r 2 When , the control method of all points on each ring (when r is the same) is the same, that is, the corresponding rotation angles are all the same, and the rotation angle is proportional to the calculated phase.

[0040]

[0041] As shown in the above formula, starting from the center of the metalens (r = 0), to the edge of the metalens (r max =R), each nanopillar on the same radius has a unique deviation in its control mode.

[0042] In this embodiment, the substrate is made of SiO2, and the nanopillars are made of TiO2. The nanopillars have a length of 390 nm to 410 nm, a width of 207 nm to 217 nm, a height of 890 nm to 910 nm, a slit width of 20 nm to 24 nm, and a substrate thickness of 290 nm to 310 nm.

[0043] The metalens utilizes a material combination of a SiO2 substrate and TiO2 nanopillars, fully leveraging the excellent optical properties and processing compatibility of both materials. The precise size of the nanopillars is designed to match the wavelength of visible light, combined with optimized slit width and substrate thickness to form a highly efficient optical control structure. Strict tolerance control of various parameters ensures the stability and consistency of device performance while maintaining good process feasibility. This structural design not only achieves excellent optical performance but also possesses good mechanical stability and reliability, making the metalens of great practical value in high-precision optical systems.

[0044] Furthermore, the length, width, and height of the rectangular TiO2 nanopillars are 400 nm, 212 nm, and 900 nm, respectively. A narrow slit with a width of 22 nm is etched along the long axis of the nanopillars. The substrate is made of 300 nm thick SiO2, and the period of the nanopillar group is 500 nm.

[0045] In this embodiment, the numerical aperture of the superlens is 0.28 to 0.82, and the operating wavelength range of the superlens is 440 nm to 670 nm. When the numerical aperture of the superlens is 0.44 to 0.6, the focal spot of the superlens is Gaussian distributed, and the full width at half maximum of the focal spot meets the diffraction limit. The focal length of the superlens is adjusted by changing the phase distribution of the nanocolumns, and the focal length of the superlens is 10 μm to 50 μm.

[0046] The metalens achieves coverage of a wide operating wavelength range and a large numerical aperture range. In particular, within the optimal operating range of numerical aperture 0.44-0.6, a diffraction-limited Gaussian distribution focal spot can be obtained, ensuring high resolution and high quality imaging. At the same time, its focal length can be continuously adjusted within the range of 10μm to 50μm by adjusting the phase distribution of the nanopillars, providing a 5-fold adjustment range. These performance characteristics give the metalens excellent imaging quality, good adjustability, and wide applicability, and it has important application value in the fields of micro-nano optical systems, high-precision imaging, and adjustable focus optical devices.

[0047] like Figure 2 and Figure 3 As shown, Figure 2 The electric field distribution diagram after the left-handed circularly polarized light is incident. After the left-handed circularly polarized light (LCP) of the superlens based on the double-coupling structure is incident on 9 groups of unit cell structures, the electric field energy is well confined in the slit and no significant leakage is observed. Figure 3 This is a schematic diagram of the phase angle distribution under six LCP monochromatic light incidents in the operating wavelength range of 520nm to 660nm. Through the fitting analysis of discrete phase points, it is found that each test wavelength group in the band has a good phase response and can perfectly cover the range of 0 to 2π. Figure 3The rotation of the nanorods with respect to the Z axis should smoothly cover the phase distribution from 0 to 2π without frequent significant jumps. Figure 1 The phase rotation angle relationship of the metalens based on the dual-coupling structure also covers the entire range from 0 to 2π.

[0048] See also Figure 4 , Figure 4 These are the simulation results of seven single-wavelength incident light incident on the dual-coupling structure superlens and the traditional superlens in the range of 520nm to 660nm. Figure 4 (a) is a superlens based on a double-coupling structure. Figure 4 (b) is a traditional superlens. The superlens based on the dual-coupling structure and the traditional superlens are placed on the XY plane, where the Z direction is the propagation direction.

[0049] like Figure 4 As shown in (a), in the analysis of the focal plane, it can be clearly observed that the Fresnel diffraction pattern near the focal spot of the metalens based on the double coupling structure is more uniformly distributed, with clear concentric or radial stripes of alternating light and dark, and no obvious inhomogeneity or bright spots off the center. Figure 4 As shown in (b), the focal spot of the traditional metalens has obvious aberrations and deviations, and even scattering spots. The emergence of these phenomena will greatly reduce the focusing efficiency and imaging quality, affecting the entire optical system. Figure 4 Where r = 12 μm, f = 50 μm, NA = 0.233, the electric field distribution under irradiation of different wavelengths from 480 nm to 650 nm is as follows Figure 4 For comparison, the electric field distribution of a conventional metalens with the same parameters at the same wavelength is shown in (a). Figure 4 As shown in (b) in .

[0050] See also Figure 5 , Figure 5 This is a schematic diagram comparing the focal position and focal spot energy of the above-mentioned metalens based on the dual-coupling structure and the traditional metalens. It is obvious that the focal length deviation of the metalens based on the dual-coupling structure and the traditional metalens is a function of the illumination wavelength. The metalens based on the dual-coupling structure also exhibits a certain chromatic aberration correction ability, and the relationship between each group of focal spot energy and the corresponding wavelength of the metalens based on the dual-coupling structure is statistically significant.

[0051] In the working wavelength range tested, Figure 5The simulated focal length distributions of a dual-coupling structure-based metalens and a conventional metalens are shown. It can be seen that under effective focusing conditions, the dual-coupling structure-based metalens significantly enhances the focal spot energy compared to the conventional metalens. It can also be seen that, under identical parameters, the focal length deviation of the dual-coupling structure-based metalens at different wavelengths is essentially constant within the normal range. However, the focusing performance of the conventional metalens is extremely poor, with significant differences in focal length deviation between adjacent wavelengths. After analyzing 14 different incident wavelength conditions and excluding those with significant influence, only six groups essentially meet standard focusing requirements. In contrast, the dual-coupling model exhibits superior focusing performance in every case. Similarly, after excluding the eight groups that failed to achieve normal focus, the comparison of focal spot energy is also very clear. Under 577nm monochromatic light incidence, the electric field intensity of the dual-coupling structure-based metalens is 3.95 times that of the conventional metalens, representing the greatest enhancement. The weakest enhancement occurs under 656nm incidence, where the focal spot energies of the two are virtually identical.

[0052] like Figure 6 As shown, Figure 6 Schematic diagram of the FWHM focal plane peak of the metalens, Figure 6 As can be seen from the left image, the full width at half maximum (FWHM) of the focal spot in each test group of the double-coupling structure-based metalens shows a relatively sharp Gaussian distribution of energy peaks without asymmetry or obvious shoulders and tails. Figure 6 As shown in the image on the right, more than half of the 14 FWHM energy peaks of the conventional PB phase metalens exhibit scattering spots, lack of a clear focus, unfocused energy (i.e., the presence of a double focus), or a noticeable shoulder. Only seven of the better quality peaks are shown here. This indicates that the energy of the metalens based on the dual-coupling structure is more concentrated at the focus and its performance is better during nonlinear transmission, with a much higher focusing efficiency than the conventional PB phase metalens.

[0053] See also Figure 7 , Figure 7 It is a statistical diagram of focusing conditions under four different numerical apertures in the visible spectrum. Figure 7 It can be seen that the metalens based on the dual-coupling structure has stable focusing ability and high focusing efficiency under four different numerical aperture (NA) conditions. Compared with the traditional structure, the improved unit model shows better focusing imaging performance in different wavelength ranges, stable focal length distribution, and significantly enhanced focal spot energy. At the same time, we found that in the main analysis of the relatively small 0.233NA, the working band will be limited to between 510nm and 680nm. When the NA gradually increases to 0.82, the working band is correspondingly extended to 440nm to 670nm, and there is no significant impact on the imaging quality compared with the traditional metalens.

[0054] Due to its extremely narrow waveguide structure, the electromagnetic field energy of the incident light is tightly confined within the slit, resulting in minimal leakage and absorption during transmission, greatly reducing energy loss. When applied to a PB phase superlens, both the final focusing efficiency and focal spot energy, two important parameters, are significantly enhanced compared to conventional PB phase superlens. In addition, significant focusing is observed in the NA range of 0.28 to 0.82. Among the five tested NA groups, the average focal spot energy of the superlens based on the dual-coupling structure is 1.2 times higher than that of the conventional superlens.

[0055] See also Figure 8 , Figure 8 The figure shows the energy-wavelength diagram of the focal spot under four different numerical apertures. The obvious spherical aberration and secondary focus are ignored in the statistics. The data is recorded as the energy at the main focal spot position. Figure 8 The focusing conditions at different NA are clearly shown. Considering that the parameters of the two models in the 500nm-660nm band are almost the same at the above NA = 0.288 and higher, the main data analysis here focuses on 500nm. The starting incident wavelength is 440nm and the step size is 7nm. The working wavelength is above 500nm with a step size of 10nm and an ending incident wavelength of 670nm. Four geometric shapes are used to mark the curves at different NA, and three special shapes are used to mark the location of focusing anomalies. If multiple anomalies occur simultaneously, the geometric shapes will be merged.

[0056] By constructing another four sets of dual-coupling structure-based superlenses with r = 15 μm and focal lengths of 40 μm, 30 μm, 20 μm and 10 μm, the focusing performance of the model at NA values ​​of 0.35, 0.44, 0.6 and 0.82 was verified and compared with the traditional superlens. The operating wavelength range was set to the entire visible spectrum of 440nm-670nm. The position, focusing conditions and focal spot energy of the two superlenses were recorded (23 sets), as shown in Figure 2. Figure 7 and Figure 8As shown. Since the initial design assumes a central wavelength of 550nm, the position of each expected focal plane in the entire spectrum should be evenly distributed above and below the focal plane at the central wavelength. There should be no discontinuities or significant fluctuations on the statistical curve. As can be seen from the figure, under four different NA groups, the focal plane displacement of the metalens based on the dual-coupling structure is consistent with expectations, and the focal plane position is evenly distributed under different NA values. Compared with the traditional metalens, it also shows fewer factors affecting the final focus (shoulders, tails, spherical aberration, bifocals). In contrast, the traditional metalens under the four NA groups shows more of the above-mentioned effects on focusing than the metalens based on the dual-coupling structure. Within the working spectrum, the traditional metalens also shows deviations from the non-smooth change of the focal plane position. Analysis of the anomalies on the statistical curve shows problems such as spherical aberration or the above-mentioned bifocals at each position, affecting the focusing efficiency. Under the three smaller NA conditions, at least two of the four focal spot formation effects occur in four different wavelength ranges, resulting in abnormal focusing and subsequent lower focal spot energy and focusing efficiency.

[0057] Moreover, under small NA (r=15, f=50, NA=0.287) and incident light below 500nm, the focusing efficiency and focal spot quality of the metalens based on the dual-coupling structure are far inferior to those of the traditional metalens. By increasing the design NA alone (keeping the diameter unchanged while shortening the design focal length), the original working defect of the metalens based on the dual-coupling structure (440nm to 520nm) gradually shows more obvious focusing behavior. The previously "disappeared" focal spot gradually becomes clear, and focusing parameters such as efficiency and focal spot energy regain their advantages over traditional metalens without obvious bifocal or spherical aberration problems affecting efficiency.

[0058] See also Figure 9 , Figure 9 Figure 2 is a statistical graph of normalized focusing efficiency versus wavelength under different initial numerical aperture conditions. The focusing efficiency of the initial two sets of metalenses under the conditions of r = 12 μm, f = 40 and the subsequent four sets of metalenses with different NAs are shown in Figure 2. Figure 9 Combined with the above distribution diagram, we found that when NA = 0.44 and 0.6, the metalens based on the dual-coupling structure exhibits the best focal spot quality and relatively high focusing efficiency, covering almost the entire visible spectrum, and all indicators can meet the conditions of mainstream applications.

[0059] Furthermore, the small aspect ratio and height-width ratio of the nanorods used are well-matched to two-photon lithography, a technique with great potential for precise nanoscale fabrication and large-scale rapid production. Compared to conventional models, the designed metalens offers significant generality and substantial improvements, with virtually no error conditions affecting focusing at a specific NA and an applicable operating spectrum that covers nearly the entire visible light range. The relatively low aspect ratio and height-width ratio also broaden the application scenarios of this promising nanofabrication technology.

[0060] By forming a dual-coupling structure through the through slits in the nanocolumns, a strong local enhancement effect of the electromagnetic field is generated, which significantly improves the phase control range and can achieve full phase coverage of 0-2π. At the same time, the dual-coupling structure enhances the interaction between light and the nanostructure. The through slit design reduces the reflection loss of light, and the light waves transmitted from the substrate will be tightly confined in the coupling structure without oscillating in the coupling structure or being absorbed / lost in the waveguide, which greatly improves the focusing efficiency and the focal spot energy of the metalens. In addition, the working bandwidth is significantly broadened to cover the visible light to near-infrared band, reducing polarization dependence, and has a good control effect on light of different polarization states. While maintaining excellent optical performance, the unified rectangular cross-section design and periodic arrangement characteristics make the device have good process compatibility and mass production capabilities.

[0061] In the description of the present invention, "multiple" means two or more, unless otherwise specifically defined. Reference to "embodiments" herein means that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A metalens based on a dual-coupling structure, characterized in that: The invention comprises a substrate and a phase wavefront disposed on the substrate, wherein the phase wavefront is composed of a plurality of periodically arranged nanopillars, and a corresponding phase distribution value is assigned according to the position of each nanopillar to convert a plane wave incident on the phase wavefront into a light beam focused at a specified focal length, wherein each nanopillar has the same rectangular cross-section and a slit is disposed in the direction of the long axis of the nanopillar, the slit penetrating the nanopillar and extending to the surface of the substrate, so that the nanopillars form a dual-coupling structure; The length of the nanocolumn is 390 nm to 410 nm, the width of the nanocolumn is 207 nm to 217 nm, the height of the nanocolumn is 890 nm to 910 nm, and the width of the slit is 20 nm to 24 nm; The straight-line distance between the geometric center points of any two adjacent nanopillars is 500 nm.

2. The metalens based on a dual-coupling structure according to claim 1, characterized in that: The expression of the phase distribution value is: ； in, φ ( x,y ) means the coordinates are ( x,y )’s lower phase distribution value, f represents the specified focal length of the phase wavefront, λ is the wavelength, x represents the abscissa of the center position of the nanorod when placed on the substrate, y The vertical coordinate represents the center position of the nanorod when placed on the substrate.

3. The metalens based on a dual-coupling structure according to claim 1, wherein: The numerical aperture of the metalens is 0.28-0.82, and the operating wavelength range of the metalens is 440 nm to 670 nm.

4. The metalens based on a dual-coupling structure according to claim 3, characterized in that: When the numerical aperture of the metalens is 0.44-0.6, the focal spot of the metalens presents a Gaussian distribution, and the full width at half maximum of the focal spot meets the diffraction limit.

5. The metalens based on a dual-coupling structure according to claim 1, wherein: The nanorods are periodically arranged on the substrate in a square close arrangement or a circular close arrangement.

6. The metalens based on a dual-coupling structure according to claim 1, wherein: The focal length of the superlens is adjusted by changing the phase distribution of the nanocolumns, and the focal length of the superlens is 10 μm to 50 μm.

7. The metalens based on a dual-coupling structure according to claim 1, wherein: The thickness of the substrate is 290nm~310nm.

8. The metalens based on a dual-coupling structure according to claim 1, wherein: The material of the substrate is SiO2, and the material of the nanorods is TiO2.

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