A planar monolithic plasmonic polaritonic superlens and a preparation method thereof

Abstract

The application discloses a planar monolithic plasmonic polaritonic superlens, which comprises a substrate layer and a plasmonic polaritonic layer arranged from bottom to top, and a stepped structure with a geometric shape is arranged on the upper surface of the plasmonic polaritonic layer; in use, the stepped structure is used for converging incident plasmonic polaritons to form a focal point. The application further provides a preparation method. The planar monolithic plasmonic polaritonic superlens is a planar monolithic device, is compatible with an existing on-chip integrated system, does not need a metal antenna, a periodic array or other auxiliary structures, has a simple manufacturing process, and can realize high-resolution and adjustable plasmonic polaritonic in-plane focusing.

Description

Technical Field

[0001] This invention belongs to the field of subwavelength electromagnetic wave modulation technology, and particularly relates to a planar monolithic polaritonic superlens and its fabrication method. Background Technology

[0002] Traditional optical lenses are limited by the diffraction limit, making it difficult to achieve subwavelength resolution. Arrays of metasurfaces or metamaterials, composed of periodic artificial microstructures, can continuously alter the phase of light, achieving beam convergence through the accumulation of phase differences. This allows them to overcome the diffraction limit and achieve subwavelength spatial resolution. However, in these arrays of metalenses, the planes containing the incident and transmitted / reflected light are typically perpendicular to the surface of the metalens, making integration into existing on-chip optical systems difficult. Furthermore, the relatively complex structure of arrays of metalenses places more stringent demands on the fabrication processes and precision required for the devices.

[0003] Polaritons are quasi-particles generated by strong coupling between photons and elementary matter, capable of compressing incident light fields in free space to the surface of a medium, with compression ratios reaching up to 10. 2 This allows for efficient modulation of light at the subwavelength scale. Traditional surface polaritons exhibit in-plane isotropic propagation modes. When the lattice structure of the medium supporting the polariton is asymmetric, it has different dielectric constants along different directions. When the dielectric constants in two of these directions have opposite signs, the polariton exhibits hyperbolic propagation. Unlike traditional surface polaritons, this hyperbolic polariton is confined within a thin layer of the medium and is therefore called a bulk local polariton. Because its propagation trajectory resembles that of a planar optical waveguide, it is also called a waveguide polariton.

[0004] The dispersion relation of waveguide-type polaritons is closely related to the thickness of the medium. At the same frequency, the in-plane momentum of a polariton is inversely proportional to the medium thickness. According to the generalized Fresnel law of refraction, a change in the in-plane momentum of a polariton will cause a reversal in its propagation direction. Therefore, by controlling the change in the thickness of the medium, the in-plane momentum of the polariton can be changed, thereby causing the polariton to refract at the interface. When the region of thickness variation has a specific planar geometry, the refracted polaritons converge, thus obtaining a polariton superlens. Thanks to the intrinsic properties of polaritons, this superlens has subwavelength and tunable resolution.

[0005] Patent document CN116203660A discloses a three-dimensional plasmonic superlens and a method for generating chiral and chiral imaging based thereon. The three-dimensional plasmonic superlens includes a silicon dioxide substrate with a metal layer disposed on the upper surface of the silicon dioxide substrate; a plurality of nanopillars passing through the metal layer and disposed on the silicon dioxide substrate, wherein the plurality of nanopillars have different heights and elliptical cross-sections, each of the elliptical cross-sections of the nanopillars has different transverse and longitudinal axis lengths, and each nanopillar cross-section rotates about the x-axis to form a different azimuth angle with respect to the longitudinal axis length of the nanopillar cross-section, and the distance between the center point of each elliptical cross-section of the nanopillar and the center point of its adjacent elliptical cross-section is the same; a metal film is disposed on the upper surface of each nanopillar. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a planar monolithic polaritonic superlens and its fabrication method. This superlens does not require a metal antenna, periodic array, or other auxiliary structures, has a simple fabrication process, and can achieve high resolution and adjustable in-plane polariton focusing to form a focal point.

[0007] To achieve the first objective of this invention, a planar monolithic polaritonic superlens is provided, comprising a substrate layer and a polariton layer disposed from bottom to top. The upper surface of the polariton layer is provided with a stepped structure of geometric shape, which focuses incident polaritons during use.

[0008] This invention utilizes the unique dispersion relation of waveguide-type polaritons and precisely controls the thickness variation of polariton materials in a specific region to change the equivalent refractive index of the system, thereby modulating the wavefront and energy flow direction of the polaritons and achieving in-plane focusing of subwavelength-scale polaritons.

[0009] Specifically, the substrate layer is made of one of the following: a metallic material, an inorganic dielectric material, or an organic polymer material.

[0010] Specifically, the polariton layer is made of one of α-phase molybdenum trioxide, α-phase vanadium pentoxide, or hexagonal boron nitride.

[0011] Specifically, the planar thickness of the polariton layer is 5 nm to 5 μm.

[0012] Specifically, the ratio of the thickness of the stepped structure to the thickness of the polariton layer plane is 1.2 to 5.

[0013] To achieve the second objective of this invention, a preparation method is provided for the above-mentioned planar monolithic polaritonical superlens, comprising the following steps:

[0014] A polariton layer is fabricated on the substrate.

[0015] A photoresist mask is fabricated on the surface of the polariton layer, and the shape of the photoresist mask is determined by the shape of the step structure.

[0016] The polariton layer surface, excluding the photoresist mask, is etched using reactive ion etching to obtain the corresponding step structure.

[0017] The etched polariton layer is cleaned to obtain a planar monolithic polaritonic superlens.

[0018] Specifically, the methods for preparing the polariton layer include mechanical exfoliation, chemical vapor deposition, or magnetron sputtering.

[0019] Specifically, the photoresist mask is 1 μm thick and is heated at 100°C and cured for 90 seconds.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The lens provided by this invention is based on the special dispersion relation of waveguide polaritons. By utilizing the confined electromagnetic field constraint effect of polaritons, it can break through the optical diffraction limit and achieve subwavelength or even deep subwavelength resolution.

[0022] Furthermore, this lens is a monolithic structure, fabricated by selective etching of the dielectric material, eliminating the need for an external micro-metal antenna or the fabrication of complex periodic microstructures, thus reducing the difficulty of device fabrication. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the planar monolithic polaritonic superlens provided in this embodiment;

[0024] Figure 2 This is a flowchart illustrating the fabrication process of the planar monolithic polaritonic superlens provided in this embodiment;

[0025] Figure 3 An atomic force microscope image of the planar monolithic polaritonic superlens provided in this embodiment;

[0026] Figure 4 This is the thickness line scan data of the planar monolithic polaritonical superlens provided in this embodiment; Figure 5 Near-field scanning microscope image of the planar monolithic polaritonic superlens provided in this embodiment;

[0027] Figure 6 This is a schematic diagram of the electromagnetic wave simulation electric field distribution of the planar monolithic polaritonic superlens provided in this embodiment.

[0028] Figure 7This is a bird's-eye view of the first type of stepped structure provided in this embodiment;

[0029] Figure 8 This is a schematic diagram of the electromagnetic wave simulation electric field distribution of the first stepped structure provided in this embodiment;

[0030] Figure 9 This is a bird's-eye view of the second type of stepped structure provided in this embodiment;

[0031] Figure 10 This is a schematic diagram of the electromagnetic wave simulation electric field distribution for the second stepped structure provided in this embodiment. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0033] The terminology used in this application is for descriptive purposes only and is not intended to limit the application. The singular forms “a,” “said,” and “the” used in this application and the appended claims are also intended to include multiple forms unless the context clearly indicates their meaning. It should be understood that although the terms first, second, third, etc., may be used in this application to describe various parts, these parameters should not be limited to these terms. These terms are used only to separate parameters of the same type from each other. For example, without departing from the scope of this application, a first step structure can also be referred to as a second step structure, and similarly, a second step structure can also be referred to as a first step structure. Depending on the context, the word “if” as used herein can be interpreted as “when…” or “in response to determination.”

[0034] This embodiment provides a planar monolithic polaritonical superlens, such as Figure 1 As shown, the device has a simple structure, consisting of a substrate 1 and a polariton layer 2 from bottom to top. The left side of the polariton layer 2 has a stepped structure with varying thickness, and the stepped structure has a specific planar geometry.

[0035] During use, when polaritons incident from the left side of polariton layer 2 propagate to the edge of the step structure, the different thicknesses on both sides of the interface result in different in-plane momentum of the polaritons. In order to satisfy the principle of momentum matching, the propagation direction of the polaritons will be refracted at the interface, so that the refracted polaritons converge at a specific distance on the right side of the step, forming the focal point of the superlens.

[0036] More specifically, in this embodiment, the substrate layer 1 is made of one of the following: a metallic material, an inorganic dielectric material, or an organic polymer material.

[0037] The polariton layer 2 is made of one of the following: α-phase molybdenum trioxide, α-phase vanadium pentoxide, or hexagonal boron nitride.

[0038] Meanwhile, the planar dimensions of the polariton layer 2 are 1μm to 500μm, and the thickness is 5nm to 5μm. The planar geometry of the step structure on the polariton layer 2 can be one of a circle, a semicircle, a fan, a triangle, or a trapezoid. In addition, the ratio of the thickness of the step structure to the planar thickness of the polariton layer 2 is 1.2 to 5.

[0039] like Figure 2 As shown, this embodiment also provides a fabrication method for the planar monolithic polaritonical superlens proposed in the above embodiments, the process of which is as follows:

[0040] A polariton layer is fabricated on the substrate.

[0041] A photoresist mask is fabricated on the surface of the polariton layer, and the shape of the photoresist mask is determined by the shape of the step structure.

[0042] The polariton layer surface, excluding the photoresist mask, is etched using reactive ion etching to obtain the corresponding step structure.

[0043] The etched polariton layer is cleared to obtain a planar monolithic polaritonic superlens.

[0044] The specific embodiments of this patent will be described in detail below with reference to the accompanying drawings:

[0045] Specific embodiment 1: The substrate 1 of this superlens is silicon dioxide, and the polariton layer 2 is α-phase molybdenum trioxide. The thickness of the thicker region on the left is 200 nm, and the thickness of the thinner region on the right is 150 nm. The planar geometry is a semi-circle with a radius of 1.4 μm. The thickness of the stepped structure is 1.3 times the thickness of the polariton layer plane.

[0046] Its preparation process includes the following steps:

[0047] Fabrication of the polariton layer: Using molybdenum trioxide powder as raw material, α-phase molybdenum trioxide crystals were grown on a silica substrate by chemical vapor deposition in an oxygen atmosphere. The heating temperature of the molybdenum trioxide powder was 750℃, the deposition temperature of the α-phase molybdenum trioxide crystals was 400℃, and the reaction time was 30 min. An α-phase molybdenum trioxide crystal with a thickness of 200 nm and a length and width greater than 10 μm was selected as the polariton layer.

[0048] Fabrication of the photoresist mask: Photoresist with a thickness of 1 μm was spin-coated onto α-phase molybdenum trioxide nanosheets and cured at 100℃ for 90 s. The planar geometry and position of the step region were determined by photolithography, and a semi-circular photoresist mask with a radius of 1.4 μm was formed after development.

[0049] Fabrication of a stepped structure with varying thickness: Reactive ion etching was used to etch the α-phase molybdenum trioxide outside the mask to a depth of 50 nm, leaving a remaining material thickness of 150 nm.

[0050] Fabrication of planar monolithic superlenses: After removing residual photoresist with solvent and drying, planar monolithic polaritonic superlenses are obtained.

[0051] like Figure 3 and Figure 4 The image shown is an atomic force microscope image of the superlens, which has a thickness of approximately 200 nm, while the remaining areas with less thickness have a thickness of 150 nm.

[0052] like Figure 5 As shown, parallel polariton interference fringes are refracted at the edge of the lens after passing through it, and the refracted polaritons converge, forming a distinct focal point on the right side of the lens.

[0053] like Figure 6 As shown, the results are highly consistent with the near-field scanning microscope images, indicating that the prepared planar monolithic polaritonic superlens can effectively converge polaritonic electromagnetic waves.

[0054] Specific Implementation Example 2: As shown in the example Figure 7 As shown, the substrate 1 of the superlens is silicon dioxide, and the polariton layer 2 is α-phase molybdenum trioxide. The thickness of the thicker region on the left is 300 nm, and the thickness of the thinner region on the right is 100 nm. The planar geometry is an isosceles triangle with a base of 4 μm and a height of 1.5 μm. The thickness of the stepped structure is three times the thickness of the polariton layer plane.

[0055] Its preparation process includes the following steps:

[0056] Fabrication of the polariton layer: Using molybdenum trioxide powder as raw material, α-phase molybdenum trioxide crystals were grown on an intrinsic silicon substrate by chemical vapor deposition in an oxygen atmosphere. The heating temperature of the molybdenum trioxide powder was 750℃, the deposition temperature of the α-phase molybdenum trioxide nanosheets was 400℃, and the reaction time was 30 min. α-phase molybdenum trioxide nanosheets with a thickness of 300 nm and a length and width greater than 10 μm were selected as the polariton layer.

[0057] Fabrication of the photoresist mask: Photoresist with a thickness of 1 μm was spin-coated onto α-phase molybdenum trioxide nanosheets and cured at 100℃ for 90 s. The planar geometry and position of the step region were determined by photolithography, and after development, an isosceles triangular photoresist mask with a base of 4 μm and a height of 1.5 μm was formed.

[0058] A stepped structure with varying thickness was fabricated. The α-phase molybdenum trioxide outside the mask was etched using reactive ion etching to a depth of 200 nm, leaving a remaining material thickness of 100 nm.

[0059] Fabrication of planar monolithic superlenses: After removing residual photoresist with solvent and drying, planar monolithic polaritonic superlenses are obtained.

[0060] like Figure 8 As shown, parallel polariton fringes are refracted at the edge of the triangular lens, and the refracted polaritons converge, forming a distinct focal point on the right side of the lens. This indicates that the fabricated planar monolithic polariton superlens can effectively converge polariton electromagnetic waves.

[0061] Specific Implementation Example 3: As shown in the example Figure 9 As shown, the substrate 1 of this superlens is quartz, and the polariton layer 2 is hexagonal boron nitride. The thickness of the thicker region on the left is 75 nm, and the thickness of the thinner region on the right is 50 nm. The planar geometry consists of a rectangle with a length of 2 μm and a width of 1 μm, with a semi-circular groove of radius 0.5 μm removed. The thickness of the stepped structure is three times the thickness of the polariton layer plane.

[0062] Its preparation process includes the following steps:

[0063] Fabrication of the polariton layer: Using hexagonal boron nitride crystals as raw material, the crystals were peeled off with adhesive tape. After repeating this process 5-10 times, the hexagonal boron nitride nanosheets on the tape were transferred to the surface of a quartz substrate. Hexagonal boron nitride nanosheets with a thickness of 75 nm and a length and width greater than 10 μm were selected as the polariton layer.

[0064] Fabrication of the photoresist mask: Photoresist with a thickness of 1 μm was spin-coated onto hexagonal boron nitride nanosheets and cured at 100℃ for 90 s. The geometry and position of the thicker areas were determined by photolithography. After development, a photoresist mask with a semi-circular groove of 0.5 μm radius was formed within a rectangle with a length of 2 μm and a width of 1 μm.

[0065] Fabrication of thickness variation interface: Reactive ion etching method is used to etch hexagonal boron nitride outside the mask to a depth of 25nm, leaving a material thickness of 50nm.

[0066] Fabrication of planar monolithic superlenses: After removing residual photoresist with solvent and drying, planar monolithic polaritonic superlenses are obtained.

[0067] like Figure 10 As shown, parallel polariton fringes are refracted at the edge of the lens after passing through the semi-circular groove. The refracted polaritons converge and form a distinct focal point on the right side of the lens, indicating that the fabricated planar monolithic polariton superlens can effectively converge polariton electromagnetic waves.

[0068] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A planar monolithic plasmonic polaritonic superlens, characterized in that, The planar monolithic plasmonic metasurface lens comprises a substrate layer and a plasmonic layer arranged from bottom to top, wherein a stepped structure with geometric shape is arranged on the upper surface of the plasmonic layer, and the stepped structure is used to converge incident plasmonic waves to form a focal point in use. The substrate layer is made of one of metal material, inorganic dielectric material and organic polymer material. The plasmonic layer is made of one of α-phase molybdenum trioxide, α-phase vanadium pentoxide and hexagonal boron nitride. The planar thickness of the plasmonic layer is 5 nm to 5 μm. The ratio of the thickness of the stepped structure to the planar thickness of the plasmonic layer is 1.2 to 5.

2. The planar monolithic plasmonic metasurface lens of claim 1, wherein, The stepped structure comprises one of circular shape, semi-circular shape, fan shape, triangular shape and trapezoidal shape.

3. A method of manufacture, characterized by, The preparation method of the planar monolithic plasmonic metasurface lens comprises the following steps: Preparation of the plasmonic layer on the substrate layer; Photoresist mask making on the surface of the plasmonic layer, wherein the shape of the photoresist mask is determined by the shape of the stepped structure; Etching of the plasmonic layer surface except the photoresist mask by using reactive ion etching method to obtain the corresponding stepped structure; Cleaning of the etched plasmonic layer to obtain the planar monolithic plasmonic metasurface lens.

4. The production method according to claim 3, characterized by, The preparation method of the plasmonic layer comprises mechanical exfoliation, chemical vapor deposition or magnetron sputtering.

5. The preparation method according to claim 3, characterized in that, The thickness of the photoresist mask is 1 μm, and the photoresist mask is heated at 100 ℃ and cured for 90 s.

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