A planar metallic metasurface lens with high focusing efficiency

Abstract

This invention relates to a high-focusing-efficiency planar metal metasurface lens, belonging to the field of microwave lenses. It comprises a dielectric layer, a metal layer, and an aperture ring. Two metal layers cover the two end faces of the dielectric layer. Several aperture rings are spaced apart on the metal layers. The aperture rings are two sets of concentric segmented circular rings with symmetrical double openings, distributed internally and externally. The opening portion of the inner ring is deflected by an angle greater than 0° along the center, causing the segmented circular rings within the aperture ring to be asymmetrically distributed, thereby achieving a focusing efficiency greater than 60% and a magnification of 16 times. This invention has the advantages of achieving high focusing efficiency and high magnification by employing an ultra-thin double-layer metal twisted double-aperture resonant ring metasurface unit and a single dielectric interlayer structure.

Description

Technical Field

[0001] This invention relates to the field of microwave lens technology, and in particular to a planar metal metasurface lens with high focusing efficiency. Background Technology

[0002] A metasurface lens is a planar ultrathin lens composed of an array of periodic metallic or dielectric metasurfaces with a gradually changing phase gradient. A metasurface is a planar subwavelength metallic or dielectric structure that allows for flexible manipulation of incident electromagnetic waves through the arrangement of periodic or quasi-periodic unit arrays. In recent years, with the proposal of the generalized Snell's law of reflection and refraction, various ultrathin devices based on metasurface technology have been continuously developed. Metasurfaces and metalenses are quasi-two-dimensional ultrathin materials that not only achieve the properties of conventional materials but also possess advantages such as thinness, low profile, low loss, simple fabrication, easy planar conformal processing, and low cost.

[0003] In optical and communication frequency bands, to overcome the high losses of metallic structures, high numerical aperture (NPAP) superlenses are generally achieved through all-dielectric metasurface structures. For example, in 2015, Arbabi et al. from Caltech achieved a high NAP superlens with a focusing efficiency of 42% using all-dielectric silicon nanopillars. In lower terahertz and microwave frequency bands, metasurfaces mostly employ periodic metal patches or complementary structures placed on dielectric substrates or air-layer surfaces, allowing for the manipulation of incident waves through the shape, geometric parameters, and arrangement of the metal metasurface structure. In the low-frequency band, high-focusing-efficiency superlenses are of significant research value for achieving ultra-compact far-field focusing, opening new research avenues for high-resolution imaging, miniaturized projection array antennas, and compact lens corner reflectors.

[0004] Currently, most high-focusing-efficiency metallic metalenses in the low-frequency band are implemented using multi-layered metallic (more than 4 layers) metasurface structures. These structures are excited by circularly polarized waves, resulting in significant device thickness, high fabrication and testing costs, and considerable implementation difficulty. Using single-layer dielectric or double-layer metallic metasurface structures can significantly reduce the design cost and implementation difficulty of metalenses. Traditional double-aperture resonant ring units have low transmittance.

[0005] Therefore, to address the above shortcomings, there is a need to provide a planar metal metasurface lens with high focusing efficiency. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] The technical problem to be solved by the present invention is to address the issues of current metasurface lenses having more than 4 metasurface layers, large unit structure thickness, and low transmittance of resonant ring units and arrays.

[0008] (II) Technical Solution

[0009] To address the aforementioned technical problems, this invention provides a planar metal metasurface lens with high focusing efficiency, comprising a dielectric layer, a metal layer, and an aperture ring. Two metal layers cover the two end faces of the dielectric layer, and a plurality of aperture rings are distributed at intervals on the metal layer. The aperture rings are two sets of concentric segmented circular rings distributed inner and outer and having symmetrical double openings. The opening portion of the inner ring is deflected at an angle greater than 0° along the center to make the segmented circular rings inside the aperture ring asymmetrically distributed, so as to achieve a focusing efficiency of more than 60% and a magnification of 16 times.

[0010] As a further explanation of the present invention, preferably, each open ring is arranged at a fixed period interval, the size of which is smaller than the wavelength of the electromagnetic wave.

[0011] As a further explanation of the present invention, preferably, the phase distribution of the metasurface lens is as follows:

[0012]

[0013] in,

[0014] The phase distribution of the metasurface lens is the inner diameter r of the inner ring of the opening ring (3);

[0015] f is the frequency of the incident electromagnetic wave;

[0016] x represents the horizontal coordinate position of the open loop;

[0017] F is the focal length of the metasurface lens.

[0018] As a further explanation of the present invention, preferably, the aperture of the metasurface lens is:

[0019] D = n0 * sin(θ)

[0020] in

[0021] D is the aperture of the metasurface lens;

[0022] n0 is the refractive index of the external environment in which the lens is located; it is 1 when the lens is in air.

[0023] θ is the maximum deflection angle of the incident electromagnetic wave.

[0024] As a further explanation of the present invention, preferably, the maximum deflection angle θ of the incident electromagnetic wave is obtained by the following formula:

[0025]

[0026] in

[0027] D is the aperture of the metasurface lens;

[0028] F is the focal length of the metasurface lens.

[0029] (III) Beneficial Effects

[0030] The above-described technical solution of the present invention has the following advantages:

[0031] This invention, through a double-opening resonant ring structure with an inner ring twist, combined with a design formula, enables metasurface lens arrays to achieve high-efficiency and large numerical aperture focusing spots in the far field. Theoretically, the projection efficiency can approach 90%, and the focusing efficiency can be greater than 60%. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the focusing operation of the metasurface lens of the present invention;

[0033] Figure 2 This is a top view of the metasurface lens opening ring unit of the present invention;

[0034] Figure 3 This is a schematic diagram of the distribution of the opening rings in the metal layer of the metasurface lens of the present invention;

[0035] Figure 4 This is a focusing energy distribution diagram of the lens of the present invention in the xz plane;

[0036] Figure 5 This is a z-axis distribution diagram of the focused energy of this invention;

[0037] Figure 6 This is the energy distribution diagram of the focused spot in the xy plane of the present invention;

[0038] Figure 7 This is the energy distribution diagram of the incident electromagnetic wave in the xy plane according to the present invention;

[0039] Figure 8 This is a normalized energy distribution diagram of the focused wave and incident electromagnetic wave along the x-axis of this invention.

[0040] In the diagram: 1. Dielectric layer; 2. Metal layer; 3. Open ring. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] A planar metallic metasurface lens with high focusing efficiency, combined with Figure 1 , Figure 3The device comprises a dielectric layer 1, a metal layer 2, and open rings 3. Two metal layers 2 cover the two end faces of the dielectric layer 1, and several open rings 3 are arrayed on the metal layers 2. The dielectric layer 1 has a disk-shaped structure with a thickness of t, preferably 2.6 mm, and a designed aperture of D, preferably 175 mm. Conventionally, increasing the thickness of the dielectric layer 1 can improve its equivalent refractive index, but this also increases the designed aperture D, leading to a decrease in focusing efficiency. This invention uses a composite structure of a double-layer periodic metal metasurface and a single-layer dielectric structure to improve the average transmittance of its gradient structure.

[0043] Combination Figure 2 , Figure 3 The open ring 3 consists of two sets of concentric segmented rings, one inside the other and one outside, with symmetrical double openings. The open rings 3 are arranged in a periodic array p in the xy plane, where p < λ, and λ is the wavelength of the incident electromagnetic wave. The outer ring portion of the open ring 3 is symmetrically distributed left and right and has a width of w2, preferably 1 mm. The inner ring has an inner diameter r, a gradually changing value, typically 1-2.25 mm. Its width is w1, preferably 1 mm. The interval between the inner and outer rings is g, preferably 1.5 mm. The opening portion of the inner ring is deflected by an angle α along the center, where α > 0°, causing the segmented rings within the open ring to be asymmetrically distributed left and right, creating a misalignment with the opening portion of the outer ring. By rationally selecting and optimizing the above data based on the actual incident electromagnetic wave data to be matched, the transmittance within the operating frequency bandwidth can be improved.

[0044] Microwave-band planar superlenses typically employ a hybrid sandwich structure of periodic metal patches (or complementary structures) and a uniform dielectric layer. To simultaneously achieve high transmittance (greater than 50%) and 360° transmission phase coverage, at least three metal layers are required. Increasing the number of stacked metal layers or the thickness of the dielectric layer can increase the equivalent refractive index of the unit cell, thus improving both transmission amplitude and transmission phase. However, this also introduces problems such as increased device weight, more complex design and fabrication processes, higher manufacturing costs, and increased testing difficulty. This invention, however, solves these problems with only two metal layers 2 and a reasonably distributed open ring 3.

[0045] The phase distribution of the aperture ring 3 of the metasurface lens is as follows:

[0046]

[0047] The phase distribution of the metasurface lens is the inner diameter r of the inner ring of the opening ring (3);

[0048] f is the frequency of the incident electromagnetic wave;

[0049] x represents the horizontal coordinate position of the open loop;

[0050] F is the focal length of the metasurface lens, preferably 100mm.

[0051] The aperture D of the metasurface lens is:

[0052] D = n0 * sin(θ)

[0053] in

[0054] n0 is the refractive index of the external environment in which the lens is located; it is 1 when the lens is in air.

[0055] θ is the maximum deflection angle of the incident electromagnetic wave, specifically:

[0056]

[0057] in

[0058] D is the aperture of the metasurface lens;

[0059] F is the focal length of the metasurface lens.

[0060] By altering the distribution of the phase gradient gradient in a double-opening resonant ring with an inner ring twist, a superlens array can be designed to achieve a high-efficiency and large numerical aperture focusing spot in the far field. Theoretically, this can make the projection efficiency of the superlens approach 90% and the focusing efficiency greater than 60%. This enables the composite structure of a double-layer periodic metallic metasurface and a single-layer dielectric structure to improve the average transmittance of its gradient gradient structure.

[0061] Combination Figures 4-8 This invention presents a double-layer ultrathin planar metallic superlens based on a phase gradient array designed with a tortuous double-opening resonant ring metasurface unit. This achieves high-efficiency focusing of incident linearly polarized electromagnetic waves and amplifies the power intensity of the incident planar electromagnetic waves by a factor of 16. The focused position is 3.3 times the wavelength λ, the half-size width of the lateral focal spot is 0.79 times the wavelength λ, and the longitudinal focusing depth is 2.8 times the wavelength. The designed single-layer metallic superlens exhibits a high focusing efficiency of 64.8%, uses the fewest metallic metasurface layers, is thinner, lighter, simpler to manufacture, and has lower cost.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A planar metallic metasurface lens with high focusing efficiency, characterized in that: The metasurface lens comprises a dielectric layer (1), a metal layer (2), and an open ring (3). Two metal layers cover the two ends of the dielectric layer (1). Several open rings (3) are spaced apart on the metal layer (2), with each open ring (3) arranged at a fixed period interval. The open rings (3) are two sets of concentric segmented rings with symmetrical double openings, distributed inside and outside. The opening portion of the inner ring is deflected by an angle greater than 0° along the center, making the segmented rings inside the open ring (3) asymmetrically distributed. The phase distribution of the metasurface lens is as follows: in, The phase distribution of the metasurface lens; The inner diameter of the inner ring of the open ring (3); The frequency of the incident electromagnetic wave; The x-coordinate position of the open loop; The focal length of the metasurface lens; To achieve a focusing efficiency of over 60% and a magnification of 16x.

2. The high-focusing-efficiency planar metal metasurface lens according to claim 1, characterized in that: The fixed period is smaller than the wavelength of the electromagnetic wave.

3. The planar metal metasurface lens with high focusing efficiency according to claim 2, characterized in that: The aperture of the metasurface lens is: in The aperture of the metasurface lens; The refractive index of the external environment in which the lens is located is 1; it is 1 when the lens is in air. This represents the maximum deflection angle of the incident electromagnetic wave.

4. A planar metal metasurface lens with high focusing efficiency according to claim 3, characterized in that: Maximum deflection angle of incident electromagnetic wave The following formula is used to calculate: in The aperture of the metasurface lens; It is the focal length of the metasurface lens.

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