Super lens based on double-coupling structure

Abstract

The invention provides a super-lens based on a double-coupling structure, and relates to the field of optical zooming, the super-lens comprises a substrate and a phase wave front arranged on the substrate, the phase wave front is composed of a plurality of nano-columns arranged periodically, a corresponding phase distribution value is given according to the position point of each nano-column, and the phase distribution value is calculated according to the position point of each nano-column. The phase wavefront is arranged on the substrate, the phase wavefront is arranged on the substrate, the phase wavefront is arranged on the phase wavefront, the nanometer columns are arranged on the phase wavefront to convert plane waves incident to the phase wavefront into light beams focused at a specified focal length, each nanometer column has the same rectangular cross section, a slit is formed in the long axis direction of each nanometer column, and the slits penetrate through the nanometer columns and extend to the surface of the substrate. And thus, the nano-columns form a double-coupling structure. According to the invention, the focusing efficiency of the super lens can be improved.

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 use the refractive index of the material and the phase accumulation of the electromagnetic wave during its transmission process to achieve beam control, but have significant disadvantages of being large and difficult to integrate. Planar superlens is an imaging lens composed of sub-wavelength units that independently controls the phase of the incident electromagnetic wave to achieve the focusing function. Compared with traditional lenses, planar superlenses are small in size, low in cost, and easy to integrate.

[0003] The Chinese patent with publication number CN116165731A discloses an intensity-tunable infrared band planar superlens and its adjustment method, including a top layer, a reflective layer and a substrate. The top layer is composed of a cylindrical unit array with symmetrical numbers of left and right units, and the radius r of multiple cylindrical units decreases from the center to both sides. The reflective layer is composed of phase change material VO2, and the substrate is composed of a dielectric. Although the above scheme forms a superlens through 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 superlens based on a dual-coupling structure to improve the focusing efficiency of the superlens. Summary of the invention

[0004] In view of this, the present invention proposes a superlens based on a double coupling structure. By forming a double coupling structure through the through slits in the nanocolumns, the light waves transmitted from the substrate will be tightly confined in the coupling structure, greatly improving the focusing efficiency and the focal spot energy of the superlens.

[0005] The present invention provides a superlens 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 nanocolumns, and a corresponding phase distribution value is assigned according to the position point of each nanocolumn, so as to convert a plane wave incident on the phase wavefront into a light beam focused at a specified focal length, wherein each nanocolumn has the same rectangular cross-section, and a slit is arranged in the long axis direction of the nanocolumn, and the slit passes through the nanocolumn and extends to the surface of the substrate, so that the nanocolumns 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 horizontal coordinate of the center position of the nanocolumn when placed on the substrate, and y represents the vertical coordinate of the center position of the nanocolumn 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 superlens is 0.28-0.82, and the operating wavelength range of the superlens is 440nm to 670nm.

[0012] More preferably, when the numerical aperture of the metalens is 0.44 to 0.6, the focal spot of the metalens is Gaussian distributed, 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 circle.

[0014] More preferably, 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.

[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 metalens. 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 nanocolumns, 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 nanocolumns 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 nanocolumns, 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

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

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

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

[0024] Figure 4 A simulation diagram for the simulation verification of 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 A schematic diagram of the FWHM focal plane peak of the metalens provided by the present invention;

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

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

[0029] Fig. 9 The 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 described embodiments 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 creative work 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-nano structures with sub-wavelength geometric dimensions.

[0033] PB phase control (also known as geometric phase control) is a classic control method of metasurfaces. It introduces geometric phase changes of light only 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 superlens 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 nanocolumns, and a corresponding phase distribution value is assigned according to the position point of each nanocolumn, so as to convert a plane wave incident on the phase wavefront into a light beam focused at a specified focal length, wherein each nanocolumn has the same rectangular cross-section, and a slit is arranged in the long axis direction of the nanocolumn, the slit passes through the nanocolumn and extends to the surface of the substrate, so that the nanocolumns 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 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 horizontal coordinate of the center position of the nanocolumn when it is placed on the substrate, and y represents the vertical coordinate of the center position of the nanocolumn when it is placed on the substrate.

[0039] The expression for the phase distribution value can determine the expected phase at 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 regulation mode.

[0042] In this embodiment, the material of the substrate is SiO2, the material of the nanorod is TiO2, the length of the nanorod is 390nm-410nm, the width of the nanorod is 207nm-217nm, the height of the nanorod is 890nm-910nm, the width of the slit is 20nm-24nm, and the thickness of the substrate is 290nm-310nm.

[0043] The superlens uses a material combination of SiO2 substrate and TiO2 nanocolumns, 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 nanocolumns matches the wavelength of visible light, combined with the optimized slit width and substrate thickness, forming an efficient optical control structure. 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, making the superlens have important practical value in high-precision optical systems.

[0044] Further, the length, width and height of the rectangular TiO2 nanorods are 400nm, 212nm and 900nm respectively. A narrow slit with a width of 22nm is etched in the axial direction of the long axis of the nanorods, the substrate is made of SiO2 with a thickness of 300nm, and the period of the nanorod group is 500nm.

[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 superlens achieves coverage of a wide operating wavelength range and a large numerical aperture range. In particular, in the optimal working 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, its focal length can be continuously adjustable in the range of 10μm to 50μm by adjusting the phase distribution of the nanocolumns, providing a 5-fold adjustment range. These performance characteristics give the superlens 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 working 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 sharp jumps. Figure 1 The phase rotation angle relationship of the metalens based on the double 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 sources in the range of 520nm to 660nm for the dual-coupling structure superlens and the traditional superlens. 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 evenly distributed, with clear alternating light and dark concentric or radial stripes, 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 superlens based on the dual-coupling structure and the traditional superlens. It is obvious that the focal length deviation of the superlens based on the dual-coupling structure and the traditional superlens is a function of the illumination wavelength. The superlens 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 superlens based on the dual-coupling structure is statistically significant.

[0051] In the working wavelength range tested, Figure 5The focal length distribution of the simulated dual-coupling structure-based superlens and the traditional superlens is shown. It can be seen that under effective focusing conditions, the focal spot energy of the superlens based on the dual-coupling structure is significantly enhanced compared with the traditional superlens. It can also be seen that under the same parameters, the focal length deviation of the superlens based on the dual-coupling structure at different wavelengths is basically a fixed value within the normal range. However, the focusing performance of the traditional superlens is extremely poor, and there is a huge difference between the focal length deviation values ​​of adjacent wavelengths. By analyzing 14 groups of different incident wavelength conditions, excluding those with greater influence, only 6 groups basically meet the standard focusing requirements. In contrast, each focusing performance of the dual-coupling model is better. Similarly, after excluding the 8 groups that cannot form normal focus, the comparison of the focal spot energy is also very clear. Under the incidence of 577nm monochromatic light, the electric field intensity of the superlens based on the dual-coupling structure is 3.95 times that of the traditional superlens, which is the largest enhancement. The weakest enhancement occurs under 656nm incidence, where the focal spot energy of the two is almost the same without difference.

[0052] like Figure 6 As shown, Figure 6 is a 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 traditional PB phase superlens show scattering spots, no clear focus, unfocused energy (i.e., there are double focuses), or obvious shoulders. Only seven of the better quality ones are shown here. This shows that the energy of the superlens based on the dual coupling structure is more concentrated at the focus, and its performance is better in the nonlinear transmission process, with a much higher focusing efficiency than the traditional PB phase superlens.

[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 obvious 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 PB phase superlenses, both the final focusing efficiency and focal spot energy, two important parameters, are significantly enhanced compared to conventional PB phase superlenses. In addition, significant focusing was 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 increased by 1.2 times compared to the conventional superlens.

[0055] See also Figure 8 , Figure 8 The focus energy wavelength diagram under four different numerical apertures, and the obvious spherical aberration and secondary focus are ignored in the statistics, and the data is recorded as the energy at the main focus 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 NA, the main data analysis here is focused 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 the ending incident wavelength is 670nm. Four geometric shapes are used to mark the curves at different NAs, 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 0.35, 0.44, 0.6 and 0.82 NA values ​​was verified and compared with the conventional superlens. The working wavelength range was set to the entire visible spectrum of 440 nm-670 nm. The positions, focusing conditions and focal spot energies of the two superlenses were recorded (23 sets), such as 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 discontinuity or significant fluctuations on the statistical curve. As can be seen from the figure, under 4 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 (shoulder, tail, spherical aberration, double focus). In contrast, the traditional metalens under 4 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 double focus at each position, affecting the focusing efficiency. Under the smaller three 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] And 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 defects of the metalens based on the dual-coupling structure (440nm to 520nm) gradually show 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 dual focus or spherical aberration problems affecting efficiency.

[0058] See also Fig. 9 , Fig. 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 superlenses under the condition of r = 12 μm, f = 40 and the subsequent four sets of superlenses with different NAs, as shown in Figure 2. Fig. 9 Combined with the above distribution diagram, we found that when NA = 0.44 and 0.6, the metalens based on the double 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 mainstream application conditions.

[0059] In addition, the small aspect ratio and height-width ratio of the nanorods used are well matched with two-photon lithography, which has great potential in precise nanoscale manufacturing and large-scale rapid preparation. Compared with the traditional model, the designed superlens has great universal significance and substantial improvement, not only has basically no error conditions affecting focusing under a specific NA, but also has an applicable working spectrum that can cover almost the entire visible light range. The relatively low aspect ratio and height-width ratio also make the application scenarios of nanofabrication technology with great potential more extensive.

[0060] A double-coupling structure is formed by the through-slits in the nanocolumns, 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 metalens. In addition, the working bandwidth is significantly broadened to cover the visible light to near-infrared band, reducing the 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 clearly and specifically limited. Reference to "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment 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 can 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 protection scope of the present invention.

Claims

1. A metalens based on a double coupling structure, characterized in that: The invention comprises a substrate and a phase wavefront arranged on the substrate, wherein the phase wavefront is composed of a plurality of periodically arranged nanocolumns, and a corresponding phase distribution value is assigned according to the position point of each nanocolumn, so as to convert a plane wave incident on the phase wavefront into a light beam focused at a specified focal length, wherein each nanocolumn has the same rectangular cross-section, and a slit is arranged in the long axis direction of the nanocolumn, and the slit passes through the nanocolumn and extends to the surface of the substrate, so that the nanocolumns form a double coupling structure.

2. A metalens based on a dual coupling structure as claimed in claim 1, characterized in that: The expression of the phase distribution value is: 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 horizontal coordinate of the center position of the nanocolumn when placed on the substrate, and y represents the vertical coordinate of the center position of the nanocolumn when placed on the substrate.

3. A superlens based on a dual coupling structure as claimed in claim 1, characterized in that: 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.

4. A superlens based on a dual coupling structure as claimed in claim 1, characterized in that: The straight-line distance between the geometric center points of any two adjacent nanorods is 500 nm.

5. The metalens based on the dual coupling structure as claimed in claim 1, characterized in that: The numerical aperture of the superlens is 0.28-0.82, and the operating wavelength range of the superlens is 440nm to 670nm.

6. A metalens based on a dual coupling structure as claimed in claim 5, 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.

7. The metalens based on the dual coupling structure as claimed in claim 1, characterized in that: The nanorods are periodically arranged on the substrate in a square close arrangement or a circular close arrangement.

8. The metalens based on the dual coupling structure as claimed in claim 1, characterized in that: The focal length of the super lens is adjusted by changing the phase distribution of the nano column, and the focal length of the super lens is 10 μm to 50 μm.

9. The metalens based on the dual coupling structure as claimed in claim 1, characterized in that: The thickness of the substrate is 290nm-310nm.

10. The metalens based on the dual coupling structure as claimed in claim 1, characterized in that: The material of the substrate is SiO2, and the material of the nanorods is TiO2.

Images