CN117706665A - Zoom superlens based on reconfigurable sparse aperture and preparation method thereof - Google Patents
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Abstract
The invention discloses a zoom superlens based on reconfigurable sparse aperture and a preparation method thereof, wherein the zoom superlens comprises a stretchable substrate and a plurality of sparse apertures; wherein the number of sparse apertures is greater than one; symmetry exists among the plurality of sparse apertures and the sparse apertures are uniformly distributed; the sparse aperture comprises a plurality of phase structures; a stretchable substrate for supporting the sparse apertures and for changing a distance between a center of the plurality of sparse apertures and a center of the stretchable substrate by deformation; sparse aperture for adjusting focal length of zoom superlens; and the phase structure is used for carrying out wave front regulation and control on the incident light. The embodiment of the invention reduces the preparation difficulty and the preparation cost, can realize the focusing performance of active regulation and control, and can be widely applied to the field of optical devices.
Description
Technical Field
The invention relates to the field of optical devices, in particular to a zoom superlens based on a reconfigurable sparse aperture and a preparation method thereof.
Background
The superlens has important roles in the fields of display imaging, wireless communication, information encryption and the like. Among them, the requirements of optical imaging for imaging resolution are continuously increasing. The angular resolution of a superlens is proportional to the ratio of the operating wavelength to the entrance pupil aperture, and increasing the aperture of a superlens is a conventional method of increasing resolution. However, the structural units of the superlens are usually in sub-wavelength scale, patterning in the manufacturing process depends on a photolithography process, and the difficulty, cost and time consumption of the photolithography process are greatly increased after the aperture is increased, so that the manufacturing difficulty is greatly increased, the production and the manufacturing are not facilitated, and the wide application of the superlens with a large aperture is limited.
In addition, in the related art, the focal length of the superlens based on the reconfigurable sparse aperture is fixed, and the adjustment of the focal length needs to be realized by adjusting and controlling the electromagnetic characteristic or the background parameter of the incident light.
Disclosure of Invention
In view of the above, an object of the embodiments of the present invention is to provide a zoom superlens based on reconfigurable sparse aperture and a preparation method thereof, which reduce preparation difficulty and preparation cost, and can realize active regulation and control of focusing performance.
In a first aspect, an embodiment of the present invention provides a zoom superlens based on reconfigurable sparse aperture, including a stretchable substrate and a plurality of sparse apertures; wherein the number of sparse apertures is greater than one; symmetry exists among the plurality of sparse apertures and the sparse apertures are uniformly distributed; the sparse aperture comprises a plurality of phase structures;
a stretchable substrate for supporting the sparse apertures and for changing a distance between a center of the plurality of sparse apertures and a center of the stretchable substrate by deformation;
sparse aperture for adjusting focal length of zoom superlens;
and the phase structure is used for carrying out wave front regulation and control on the incident light.
Optionally, the stretchable substrate comprises any one of a flexible substrate, an elastic substrate, or a malleable substrate.
Optionally, the stretchable substrate comprises a central electrode, a plurality of spring structures, a plurality of comb electrodes, and a plurality of peripheral electrodes; the central electrode is arranged at the central position of the stretchable substrate; a plurality of spring structures, a plurality of sparse apertures, a plurality of comb-shaped electrodes and a plurality of peripheral electrodes are sequentially arranged in the direction from the central electrode to the edge of the stretchable substrate; wherein,
a center electrode for supplying a first voltage to one end of the comb-shaped electrode;
a peripheral electrode for supplying a second voltage to the other end of the comb-shaped electrode;
the spring structure is used for generating deformation so as to change the distance between the centers of the plurality of sparse apertures and the center of the stretchable substrate;
and the comb-shaped electrode is used for generating electrostatic force so as to deform the spring structure.
Optionally, the spring structure, the sparse aperture and the comb electrode are suspended by a pulling force between the spring structure and the center electrode and a pulling force between the comb electrode and the peripheral electrode.
Optionally, the shape of the sparse aperture comprises a first regular shape comprising any one or more of a sector, a circle, or a rectangle.
Optionally, the plurality of sparse apertures are symmetrical about a center of the stretchable substrate or symmetrical about a line passing through the center of the stretchable substrate.
Optionally, the plurality of sparse apertures form a plurality of focusing units; symmetry exists for sparse apertures in the same focusing element.
Optionally, the sparse aperture further comprises a rigid substrate, etching is performed on the rigid substrate to form a phase structure; the cross-sectional shape of the phase structure includes a second regular pattern including a T-shape or a circle shape.
In a second aspect, an embodiment of the present invention further provides a method for preparing a zoom superlens based on a reconfigurable sparse aperture, which is applied to the zoom superlens described above, and includes:
pretreating a substrate;
preparing a plurality of bonding layers and a stretchable substrate on the pretreated substrate;
preparing a sparse aperture layer at a preset position, and preparing sparse apertures in the sparse aperture layer;
the substrate and the bonding layer corresponding to the substrate are removed.
Optionally, when the stretchable substrate includes a center electrode, a plurality of spring structures, a plurality of comb electrodes, and a plurality of peripheral electrodes, the preparation method includes:
preparing a protective layer, a bonding layer and a sparse aperture layer on a substrate in sequence;
preparing a sparse aperture, a spring structure and a comb structure in the sparse aperture layer;
preparing comb-shaped electrodes on the comb-tooth structure;
and removing part of the substrate and part of the bonding layer to suspend the sparse aperture, the spring structure and the comb-shaped electrode.
The embodiment of the invention has the following beneficial effects: the embodiment of the invention provides a zoom superlens based on a reconfigurable sparse aperture and a preparation method thereof, wherein the zoom superlens comprises a stretchable substrate and a plurality of sparse apertures; wherein the number of sparse apertures is greater than one; symmetry exists among the plurality of sparse apertures and the sparse apertures are uniformly distributed; the sparse aperture comprises a plurality of phase structures; the stretchable substrate is used for supporting the sparse apertures and enabling the distances between the centers of the plurality of sparse apertures and the center of the stretchable substrate to change through deformation; sparse aperture for adjusting focal length of zoom superlens; and the phase structure is used for carrying out wave front regulation and control on the incident light. By stretching the stretchable substrate, active regulation and control of the focal length of the superlens are realized, and the focal length is linearly related to the stretching amount of the substrate, so that regulation and control are facilitated; the number and arrangement of the sparse apertures can be freely designed according to actual requirements, and the method has higher flexibility; a plurality of sparse apertures in the same zoom superlens can form a plurality of focusing units, so that the spatial multiplexing of the sparse apertures is realized; the distance between the center of the sparse aperture in different focusing units and the center of the stretchable substrate is changed differently, and independent regulation and control of a plurality of focusing units are realized. The preparation method of the embodiment of the invention relates to photoetching, ion etching, bonding and ion beam evaporation technology, and is used for preparing the structure in the varifocal superlens layer by layer, has simple process flow, reduces the preparation difficulty and the preparation cost, and is beneficial to wide production and application.
Drawings
Fig. 1 is a schematic structural diagram of a zoom superlens based on a reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the structure and electric field of a zoom superlens based on a reconfigurable sparse aperture according to an embodiment of the present invention;
fig. 3 is a schematic perspective view of a zoom superlens based on a reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a three-dimensional structure of another zoom superlens based on a reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of the structure, electric field and focusing performance of a zoom superlens based on biaxial stretching and reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of the structure, electric field and focusing performance of a zoom superlens based on four-axis stretching and reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of the structure, electric field and focusing performance of a zoom superlens based on uniaxial stretching and reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of the structure, electric field and focusing performance of another zoom superlens based on biaxial stretching and reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of the structure, electric field and focusing performance of another zoom superlens based on four-axis stretching and reconfigurable sparse aperture according to an embodiment of the present invention;
fig. 10 is a schematic flow chart of a preparation method of a zoom superlens based on a reconfigurable sparse aperture according to an embodiment of the present invention;
FIG. 11 is a schematic flow chart of another method for preparing a zoom superlens based on a reconfigurable sparse aperture according to an embodiment of the present invention;
fig. 12 is a schematic flow chart of another method for preparing a zoom superlens based on a reconfigurable sparse aperture according to an embodiment of the present invention.
Detailed Description
The invention will now be described in further detail with reference to the drawings and to specific examples. The step numbers in the following embodiments are set for convenience of illustration only, and the order between the steps is not limited in any way, and the execution order of the steps in the embodiments may be adaptively adjusted according to the understanding of those skilled in the art.
In the following description, reference is made to "some embodiments" which describe a subset of all possible embodiments, but it is to be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with one another without conflict.
In the following description, the terms "first", "second", "third" and the like are merely used to distinguish similar objects and do not represent a specific ordering of the objects, it being understood that the "first", "second", "third" may be interchanged with a specific order or sequence, as permitted, to enable embodiments of the invention described herein to be practiced otherwise than as illustrated or described herein.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the embodiments of the invention is for the purpose of describing embodiments of the invention only and is not intended to be limiting of the invention.
As shown in fig. 1, an embodiment of the present invention provides a zoom superlens based on a reconfigurable sparse aperture 2, comprising a stretchable substrate 1 and a plurality of sparse apertures 2; wherein the number of sparse apertures 2 is greater than one; symmetry exists among the plurality of sparse apertures 2, and the sparse apertures are uniformly distributed; the sparse aperture 2 comprises a plurality of phase structures 21;
a stretchable substrate 1 for supporting the sparse apertures 2 and for changing the distance between the center of the plurality of sparse apertures 2 and the center of the stretchable substrate 1 by deformation;
a sparse aperture 2 for adjusting the focal length of the zoom superlens;
a phase structure 21 for wavefront manipulation of the incident light.
Specifically, the sparse aperture 2 is arranged on the stretchable substrate 1, or the stretchable substrate 1 comprises a plurality of parts, the two sides of the sparse aperture 2 are respectively connected with the stretchable substrate 1, and the sparse aperture 2 is suspended below; the number of the sparse apertures 2 is more than one, so that a symmetrical structure can be formed among a plurality of the sparse apertures 2; the sparse apertures 2 are provided with a sufficient number of phase structures 21 to realize wave front regulation of incident light through the phase structures 21, and the focusing of the zoom superlens is realized by changing the distances between the centers of the plurality of sparse apertures 2 and the center of the stretchable substrate 1 by stretching or compressing the stretchable substrate 1.
Specifically, the incident light may be incident from the direction of the sparse aperture 2 to the stretchable substrate 1, or from the direction of the stretchable substrate 1 to the sparse aperture 2.
Specifically, the center of one sparse aperture 2 is connected to the center of the stretchable substrate 1 in an axis, and each sparse aperture 2 is moved on the axis by stretching or compressing the stretchable substrate 1, so that the distance between the center of the sparse aperture 2 and the center of the stretchable substrate 1 is increased or decreased.
In one specific embodiment, as shown in fig. 2 (a), the sparse aperture has dimensions of 3mm x 4.5mm; as shown in fig. 2 (a) - (c), when the sparse apertures were shifted 3mm, 4.5mm and 9mm, respectively, in the lateral direction; the normalized electric field distribution of the emitted light shifted by 3mm is shown in fig. 2 (d), the normalized electric field distribution of the emitted light shifted by 4.5mm is shown in fig. 2 (e), and the normalized electric field distribution of the emitted light shifted by 9mm is shown in fig. 2 (f); wherein, the electric field intensity is black when 0, and white when 1. As can be seen from (d) - (f) in fig. 2, the electric field energy distribution at the focus is tilted, wherein the focus is at the maximum of the electric field along the central axis of the zoom superlens; as the sparse aperture moves, the focal length of the single sparse aperture will change, but the electric field distribution will be off-center. Therefore, it is necessary to maintain the center distribution of the electric field and change the focal length by increasing the number of sparse apertures and making symmetry exist between several sparse apertures; the electric field synthesis of the zoom superlens based on two sparse apertures with central symmetry is as shown in (g) of fig. 2, and the position relationship of the two sparse apertures from left to right is respectively approaching, original position and far; when the two sparse apertures are close, the focuses of the two sparse apertures are not overlapped any more, and the focal length is reduced; when the two sparse holes are far away, the focuses of the two sparse holes are not coincident any more, and the focal length is increased. By making the two sparse apertures close to or far from each other, the distribution of the composite electric field can be correspondingly changed, and the position of the electric field maximum value along the central axis direction of the zoom superlens can be changed, so that the effective regulation and control of the focal length of the superlens can be realized.
Optionally, the stretchable substrate comprises any one of a flexible substrate, an elastic substrate, or a malleable substrate.
Specifically, when the stretchable substrate is any one of a flexible substrate, an elastic substrate, or a stretchable substrate, the sparse aperture is provided on the stretchable substrate, and an external force is applied to the stretchable substrate on an axis line formed by connecting the center of the sparse aperture and the center of the stretchable substrate, so that a distance between the center of the sparse aperture and the center of the stretchable substrate is changed.
Specifically, when the stretchable substrate is a flexible substrate, the zoom superlens as shown in (a) of fig. 3 is uniaxially stretched, and the number of sparse apertures is 2; the zoom superlens shown in fig. 3 (b) is biaxially stretched, and the number of sparse apertures is 4; the zoom superlens shown in fig. 3 (c) is stretched in four axes, and the number of sparse apertures is 8.
In particular, a flexible substrate refers to a base material having relatively high flexibility and bendability capable of withstanding multiple bending and deformation without breaking or damaging. The material of the flexible substrate includes any one of a polymer film, a thin metal foil, a plastic film, etc., and the specific flexible substrate material is determined according to practical situations, and the embodiment of the present invention is not limited, and only examples are provided for reference, for example, the material of the flexible substrate may be Polydimethylsiloxane (PDMS).
Specifically, the elastic substrate refers to a base material having high elasticity and recovery, which is capable of being deformed by an external force, but is capable of being quickly recovered after the external force is removed. The material of the elastic substrate includes an elastomer material or an elastic film, and the specific elastic substrate material is determined according to practical situations, which is not limited in the embodiment of the present invention.
In particular, an extensible substrate refers to a base material that is highly extensible and stretchable and is capable of substantial stretching and deformation under external forces without breaking or losing functionality. The material of the extensible substrate includes an elastomer material or an elastic polymer film, and the specific elastically extensible substrate material is determined according to practical situations, which is not limited in the embodiment of the present invention.
As shown in fig. 4, the stretchable substrate 1 includes a central electrode 11, a number of spring structures 12, a number of comb-like electrodes 13, and a number of peripheral electrodes 14; the center electrode 11 is provided at the center position of the stretchable substrate 1; a plurality of spring structures 12, a plurality of sparse apertures 2, a plurality of comb-shaped electrodes 13 and a plurality of peripheral electrodes 14 are sequentially arranged in the direction from the central electrode 11 to the edge of the stretchable substrate 1; wherein,
a center electrode 11 for supplying a first voltage to one end of the comb-shaped electrode 13;
a peripheral electrode 14 for supplying a second voltage to the other end of the comb-shaped electrode 13;
a spring structure 12 for deforming to vary the distance between the center of the plurality of sparse apertures 2 and the center of the stretchable substrate 1;
and comb-shaped electrodes 13 for generating electrostatic forces to deform the spring structure 12.
Specifically, the stretchable substrate 1 is composed of a central electrode 11, a plurality of spring structures 12, a plurality of comb-shaped electrodes 13 and a plurality of peripheral electrodes 14; a plurality of spring structures 12, a plurality of sparse apertures 2, a plurality of comb-shaped electrodes 13 and a plurality of peripheral electrodes 14 are sequentially connected outwards by taking the central electrode 11 as the center; wherein the number of spring structures 12, comb electrodes 13 and peripheral electrodes 14 is the same as the number of sparse apertures 2.
Specifically, the comb-shaped electrodes 13, which are also referred to as interdigital electrodes, are composed of alternately arranged metal electrodes, forming comb-shaped motor teeth. The spacing between the electrode teeth is typically very close, forming a few fine gaps.
Specifically, when the stretchable substrate 1 includes the center electrode 11, the plurality of spring structures 12, the plurality of comb-shaped electrodes 13, and the plurality of peripheral electrodes 14, stretching of the stretchable substrate 1 is achieved by a microelectromechanical system (Micro Electro Mechanical Systems, MEMS).
Specifically, two different voltages, such as a positive voltage and a negative voltage, are applied to the center electrode 11 and the peripheral electrode 14, respectively, so that an attractive electrostatic force is generated between the electrode teeth which are mutually intersected in the comb-shaped electrode 13, the electrode teeth are mutually close to each other, so that the spring structure 12 is stretched, and the distance between the center of the sparse aperture 2 and the center of the stretchable substrate 1 is increased; when the potential difference between the first voltage and the second voltage is reduced, the degree of stretching of the spring structure 12 is reduced such that the distance between the center of the sparse aperture 2 and the center of the stretchable substrate 1 is reduced.
Specifically, when the stretchable substrate 1 includes a center electrode 11, a plurality of spring structures 12, a plurality of comb-shaped electrodes 13, and a plurality of peripheral electrodes 14, the zoom superlens as shown in (a) of fig. 4 is uniaxially stretched, and the number of sparse apertures 2 is 2; the zoom superlens shown in fig. 4 (b) is biaxially stretched, and the number of sparse apertures 2 is 4; the zoom superlens shown in fig. 4 (c) is stretched in four axes, and the number of sparse apertures 2 is 8.
Optionally, the spring structure, the sparse aperture and the comb electrode are suspended by a pulling force between the spring structure and the center electrode and a pulling force between the comb electrode and the peripheral electrode.
Specifically, the sparse aperture, the spring structure and the comb electrode are in a suspended state, so that when electrostatic force is generated between electrode teeth which are mutually intersected in the comb electrode, the spring structure can deform, and the sparse aperture moves.
Specifically, the bottoms of the central electrode, the peripheral electrode and/or part of the comb-shaped electrodes are connected with a protective layer and a substrate to support the central electrode, the spring structure, the sparse aperture, the comb-shaped electrodes and the peripheral electrode, so that the sparse aperture, the spring structure and the comb-shaped electrodes are suspended by the tensile force between the spring structure and the central electrode and the tensile force between the comb-shaped electrodes and the peripheral electrode; the bottom of part of the comb-shaped electrode is connected with the protective layer and the substrate, so that when electrostatic force is generated between the electrode teeth which are mutually intersected in the comb-shaped electrode, the electrode teeth can move, but cannot be fixed by the protective layer or the substrate, and the electrode teeth cannot move.
Optionally, the shape of the sparse aperture comprises a first regular shape comprising any one or more of a sector, a circle, or a rectangle.
Specifically, the first regular shape includes any one or more of a sector, a circle, or a rectangle, and the specific shape is determined according to practical situations, which is not limited in the embodiments of the present invention, and only examples are provided for reference, for example, the first regular shape may be a rectangle.
Optionally, the plurality of sparse apertures are symmetrical about a center of the stretchable substrate or symmetrical about a line passing through the center of the stretchable substrate.
Specifically, when the shape of the sparse aperture is itself an axisymmetric pattern, the symmetry of the plurality of sparse apertures about the center of the stretchable substrate is equivalent to the axisymmetry about the center passing through the stretchable substrate; when the shape of the sparse apertures is itself a non-axisymmetric pattern, such as a non-equilateral triangle or a non-isosceles triangle, the number of sparse apertures are symmetric about the center of the stretchable substrate and are symmetric about an axis passing through the center of the stretchable substrate in two different symmetric ways.
Optionally, the plurality of sparse apertures form a plurality of focusing units; symmetry exists for sparse apertures in the same focusing element.
Specifically, one or more focusing units may be included in one zoom superlens; the number of sparse apertures in one focusing unit is greater than one, and symmetry exists in the sparse apertures in the same focusing unit.
In a specific embodiment, the zoom superlens is structured as shown in FIG. 5 (a), comprising four sparse apertures 201-204; wherein the sparse aperture 201 and the sparse aperture 203 form one focusing unit, and the sparse aperture 202 and the sparse aperture 204 form the other focusing unit. Compressing or stretching the stretchable substrate along the long side direction of the sparse aperture, wherein the normalized electric field energy of the emergent light is shown as (b) in fig. 5, and the compressing is performed towards the center of the stretchable substrate, and the compressing is expressed as a negative moving distance; stretching is performed in a direction away from the center of the stretchable substrate, expressed as a positive distance of movement. The change of the focusing characteristics of the transverse magnetic mode and the transverse electric mode of the outgoing light with the movement is shown in fig. 5 (c) - (f), wherein (c) - (d) are the focusing characteristic diagrams of the two focusing units in the transverse magnetic mode, and (e) - (f) are the focusing characteristic diagrams of the two focusing units in the transverse electric mode; the graph shows that the full width at half maximum of the emergent light exceeds or approaches to the diffraction limit, which indicates that the zoom superlens has excellent focusing quality and can realize the linear change of the focal length; wherein, in the transverse magnetic mode, the linear correlation coefficients of the focal lengths of the two focusing units are 0.99772 and 0.99908 in sequence; in the transverse electric mode, the linear correlation coefficients of the focal lengths of the two focusing units are 0.99877 and 0.99705 in order.
In another specific embodiment, the structure of the zoom superlens is as shown in fig. 6 (a), comprising eight sparse apertures; wherein the sparse apertures 205, 207, 209, 212 constitute one focusing element and the sparse apertures 206, 208, 210, 213 constitute another focusing element. The stretchable substrate is compressed or stretched along the long side direction of the sparse aperture, and the normalized electric field energy of the emitted light is shown in fig. 6 (b). The change of focusing characteristics of the transverse magnetic mode and the transverse electric mode of the emergent light along with the movement is shown in (c) - (d) of fig. 6, and the full width at half maximum of the emergent light can exceed or approach the diffraction limit, which indicates that the zoom super-lens has excellent focusing quality and can realize the linear change of the focal length; in the transverse magnetic mode, the linear correlation coefficients of the focal lengths of the two focusing units are 0.99416 and 0.99955 in sequence; in the transverse electric mode, the linear correlation coefficients of the focal lengths of the two focusing units are 0.99967 and 0.99866 in order.
Optionally, the sparse aperture further comprises a rigid substrate, etching is performed on the rigid substrate to form a phase structure; the cross-sectional shape of the phase structure includes a second regular pattern including a T-shape or a circle shape.
Specifically, the specific second rule pattern is determined according to the actual situation, which is not limited in the embodiment of the invention, and only the embodiment is provided for reference, for example, the second rule pattern may be T-shaped.
Specifically, the material of the sparse pore diameter includes a rigid material, the rigid material includes silicon, and specifically, the sparse pore diameter material is determined according to practical situations, which is not limited in the embodiment of the present invention.
Specifically, the sparse aperture further comprises a rigid substrate, and etching is performed on the rigid substrate to form a phase structure, namely, a layer of rigid material exists between the phase structure and the stretchable substrate, so that when the stretchable substrate deforms, the deformation of the sparse aperture has negligible influence on focusing and focusing effects of the zoom superlens.
Specifically, the phase structure includes a polarization dependent phase structure such that the outgoing light transmitted through the zoom superlens achieves a transverse magnetic mode and a transverse electric mode.
In a specific embodiment, the cross-sectional shape of the phase structure is T-shaped, and the T-shaped phase structure has polarization dependent properties, enabling focusing in two polarization directions.
In a specific embodiment, a single axis stretched sparse aperture based zoom superlens is shown in FIG. 1, the stretchable substrate being a flexible substrate; the number of sparse apertures is 2, symmetrical about the center of the stretchable substrate; the sparse aperture is rectangular in shape, and the phase structure is of a T-shaped cross section. The focal length of the superlens is changed by stretching the flexible substrate along the long side direction of the sparse aperture.
In a specific embodiment, a uniaxially stretched reconfigurable sparse aperture based zoom superlens (stretchable single-axis metals, SSM) is structured as shown in fig. 7 (a), comprising two rectangular sparse apertures; the stretchable substrate stretches along the long side direction of the rectangle, the normalized electric field energy of the emergent light is shown in (b) of fig. 7, and as can be seen from the figure, SSM keeps good focusing characteristic in the axial direction, and the focal length increases with the increase of the moving amount; wherein compression toward the center of the stretchable substrate is expressed as a negative travel distance; stretching is performed in a direction away from the center of the stretchable substrate, expressed as a positive distance of movement. The change of the focusing characteristic of the outgoing light with the movement in the transverse magnetic mode is shown in fig. 7 (c), the change of the focusing characteristic with the movement in the transverse electric mode is shown in fig. 7 (d), the moving distance of the sparse aperture is increased from-500 μm to 500 μm in a step of 250 μm, the focal length is kept linearly increased in both the transverse magnetic mode and the transverse electric mode, the linear correlation coefficient of the transverse magnetic mode is 0.99804, and the linear correlation coefficient of the transverse electric mode is 0.99855. The full width at half maximum characterizes the focusing performance of the zoom superlens, and the full width at half maximum in the longitudinal and transverse directions are very close to or even exceed the diffraction limit as shown in figures (c) - (d).
In another specific embodiment, the structure of the biaxially stretched reconfigurable sparse aperture based zoom Superlens (SDM) is shown in fig. 8 (a), and includes four rectangular sparse apertures, which are the same focusing unit; the stretchable substrate stretches along the long side direction of the rectangle, and the normalized electric field energy of the emitted light is as shown in fig. 8 (b), and it can be seen from the figure that SDM maintains good focusing characteristics in the axial direction, and the focal length increases with the increase of the moving amount. The change of the focusing characteristic of the emergent light along with the movement in the transverse magnetic mode is shown in fig. 8 (c), the change of the focusing characteristic along with the movement in the transverse electric mode is shown in fig. d, it can be seen from the graph that the full widths at half maximum in the longitudinal direction and the full width at half maximum in the transverse direction are very close to the diffraction limit, the focal length of the SDM shows good linear change trend along with the movement distance of the sparse aperture, the linear correlation coefficient of the transverse magnetic mode is 0.99852, and the linear correlation coefficient of the transverse electric mode is 0.99858.
In another specific embodiment, a four-axis stretched reconfigurable sparse aperture based zoom Superlens (SQM) has a structure as shown in fig. 9 (a), comprising eight rectangular sparse apertures, the eight rectangular sparse apertures being the same focusing unit; the stretchable substrate stretches along the long side direction of the rectangle, the normalized electric field energy of the emitted light is as shown in fig. 9 (b), and it can be seen from the figure that the SQM maintains good focusing characteristics in the axial direction, and the focal length increases with the increase of the moving amount. The change of the focusing characteristic of the emergent light along with the movement in the transverse magnetic mode is shown in fig. 9 (c), the change of the focusing characteristic along with the movement in the transverse electric mode is shown in fig. 9 (d), the longitudinal half-width and the transverse half-width are very close to diffraction limit, the focal length of SDM shows good linear change trend along with the movement distance of the sparse aperture, the linear correlation coefficient of the transverse magnetic mode is 0.99655, and the linear correlation coefficient of the transverse electric mode is 0.99862.
As shown in fig. 10, the embodiment of the invention further provides a preparation method of a zoom superlens based on a reconfigurable sparse aperture, which is applied to the zoom superlens described above, and includes:
s100, preprocessing the substrate 3.
Specifically, the material of the substrate includes silicon or silicon dioxide, and the specific substrate material is determined according to practical situations, and the embodiment of the invention is not limited, but only provided for reference, for example, the material of the substrate is silicon as shown in the figure.
Specifically, the pretreatment includes cleaning the substrate 3.
Specifically, the substrate 3 serves as a temporary substrate so that the vacuum adsorption process involved in performing photolithography does not affect the flexible substrate.
S200, preparing a plurality of bonding layers and a stretchable substrate on the pretreated substrate 3; the stretchable substrate comprises any one or more of a flexible substrate, a center electrode, a plurality of spring structures, a plurality of comb electrodes, and a plurality of peripheral electrodes.
Specifically, when the stretchable substrate is a flexible substrate, a plurality of bonding layers and the stretchable substrate are prepared on the pretreated substrate, specifically including:
s201, as shown in fig. 11 (a), a first bonding layer 4 and a flexible substrate 5 are sequentially prepared on the pretreated substrate 3.
Specifically, the material of the flexible substrate 5 includes any one of Polydimethylsiloxane (PDMS), polyester (PET) or Polyimide (PI), and the specific material of the flexible substrate 5 is determined according to practical situations, and the embodiment of the invention is not limited, but only provided for reference, for example, the flexible substrate 5 is PDMS as shown in the drawings.
S300, preparing a sparse aperture layer 6 at a preset position, and preparing sparse apertures in the sparse aperture layer 6.
S301, as shown in (b) - (c) of FIG. 11, cleaning the sparse aperture layer 6, carrying out local patterning on the sparse aperture layer 6 through photoetching and deep reactive ion etching, and bonding the local patterned sparse aperture layer 6 on a preset position of the flexible substrate 5 through a second bonding layer 7, so that the local patterned sparse aperture layer 6 is uniformly distributed on the flexible substrate and has symmetry;
s302, as shown in (d) of fig. 11, performing secondary alignment lithography and deep reactive ion etching on the partially patterned sparse aperture layer 6, and etching the phase structure 21 to obtain a sparse aperture 2.
Specifically, the material of the sparse pore diameter 2 includes silicon, and the specific sparse pore diameter material is determined according to practical situations, and the embodiment of the invention is not limited, but only provided for reference, for example, the material of the sparse pore diameter as shown in the figure is silicon.
Specifically, the material of the first bonding layer 4 or the second bonding layer 7 includes an organic glue, and the specific bonding layer material is determined according to practical situations, but the embodiment of the invention is not limited thereto, and only examples are provided for reference, for example, two different organic glues are respectively used for the first bonding layer 4 and the second bonding layer 7 as shown in the drawings.
S400, removing the substrate 3 and the bonding layer corresponding to the substrate 3.
Specifically, as shown in (e) of fig. 11, the substrate 3 and the first bonding layer 4 are removed, resulting in a stretchable substrate based on a flexible substrate and a variable focus superlens of reconfigurable sparse aperture.
In a specific embodiment, a solution that dissolves the first bonding layer 4 but not the second bonding layer 7 is used to remove the substrate and the first bonding layer 4.
Optionally, when the stretchable substrate includes a central electrode, a plurality of spring structures 12, a plurality of comb electrodes 13 and a plurality of peripheral electrodes, the preparation method of the zoom superlens based on the reconfigurable sparse aperture includes:
s500, preparing a protective layer 8, a bonding layer and a sparse aperture layer 6 on the substrate 3 in sequence.
S501, as shown in fig. 12 (a), a protective layer 8 is prepared on a substrate 3, where a material of the protective layer 8 includes silicon dioxide, and a specific protective layer material is determined according to practical situations, and the embodiment of the invention is not limited, and only examples are provided for reference, for example, the material of the protective layer 8 shown in fig. 12 (a) is silicon dioxide;
s502, as shown in (b) of fig. 12, a third bonding layer 9 and a sparse aperture layer 6 are sequentially prepared on the protective layer 8, and an alignment mark penetrating the entire structure is etched in the structure shown in (b) of fig. 12 by photolithography and deep reactive ion etching.
S600, preparing sparse apertures, spring structures 12 and comb structures 15 in the sparse aperture layer 6.
Specifically, as shown in fig. 12 (d) - (e), the sparse aperture layer 6 is partially patterned by photolithography and deep reactive ion etching, and the partially patterned sparse aperture layer 6 is subjected to secondary alignment photolithography and deep reactive ion etching to etch out the phase structure 21, the spring structure 12 and the comb-teeth structure 15, thereby obtaining the sparse aperture 2.
And S700, preparing the comb-shaped electrode 13 on the comb-tooth structure 15.
Specifically, as shown in fig. 12 (f), electron beam evaporation is performed on the comb-tooth structure 15 to obtain a metal electrode, and patterning of the metal electrode is achieved by a lift-off (liftoff) process to obtain the comb-shaped electrode 13.
S800, removing part of the substrate and part of the bonding layer to suspend the sparse aperture, the spring structure 12 and the comb-shaped electrode 13.
Specifically, as shown in (g) - (h) of fig. 12, part of the substrate 3 and the protective layer 8 are removed by photolithography and deep reactive ion etching to suspend the sparse aperture, the spring structure 12, and part of the comb-shaped electrode 13.
The embodiment of the invention has the following beneficial effects: the embodiment of the invention provides a zoom superlens based on a reconfigurable sparse aperture and a preparation method thereof, wherein the zoom superlens comprises a stretchable substrate and a plurality of sparse apertures; wherein the number of sparse apertures is greater than one; symmetry exists among the plurality of sparse apertures and the sparse apertures are uniformly distributed; the sparse aperture comprises a plurality of phase structures; the stretchable substrate is used for supporting the sparse apertures and enabling the distances between the centers of the plurality of sparse apertures and the center of the stretchable substrate to change through deformation; sparse aperture for adjusting focal length of zoom superlens; and the phase structure is used for carrying out wave front regulation and control on the incident light. By stretching the stretchable substrate, active regulation and control of the focal length of the superlens are realized, and the focal length is linearly related to the stretching amount of the substrate, so that regulation and control are facilitated; the number and arrangement of the sparse apertures can be freely designed according to actual requirements, and the method has higher flexibility; a plurality of sparse apertures in the same zoom superlens can form a plurality of focusing units, so that the spatial multiplexing of the sparse apertures is realized; by adopting a stretchable substrate based on a micro-electro-mechanical system (MEMS), the distance between the center of the sparse aperture in different focusing units and the center of the stretchable substrate is changed differently, and independent regulation and control of a plurality of focusing units are realized. The preparation method of the embodiment of the invention relates to photoetching, ion etching, bonding and ion beam evaporation technology, and is used for preparing the structure in the varifocal superlens layer by layer, has simple process flow, reduces the preparation difficulty and the preparation cost, and is beneficial to wide production and application.
While the preferred embodiment of the present invention has been described in detail, the invention is not limited to the embodiment, and various equivalent modifications and substitutions can be made by those skilled in the art without departing from the spirit of the invention, and these modifications and substitutions are intended to be included in the scope of the present invention as defined in the appended claims.
Claims (10)
1. The zoom superlens based on the reconfigurable sparse aperture is characterized by comprising a stretchable substrate and a plurality of sparse apertures; wherein the number of sparse apertures is greater than one; symmetry exists among the plurality of sparse apertures, and the sparse apertures are uniformly distributed; the sparse aperture comprises a plurality of phase structures;
the stretchable substrate is used for supporting the sparse apertures and changing the distances between the centers of the sparse apertures and the centers of the stretchable substrate through deformation;
the sparse aperture is used for adjusting the focal length of the zoom super lens;
the phase structure is used for carrying out wave front regulation and control on incident light.
2. The reconfigurable sparse aperture based zoom superlens of claim 1, wherein the stretchable substrate comprises any one of a flexible substrate, an elastic substrate, or a malleable substrate.
3. The reconfigurable sparse aperture based zoom superlens of claim 1, wherein the stretchable substrate comprises a central electrode, a number of spring structures, a number of comb electrodes, and a number of peripheral electrodes; the center electrode is arranged at the center of the stretchable substrate; a plurality of spring structures, a plurality of sparse apertures, a plurality of comb-shaped electrodes and a plurality of peripheral electrodes are sequentially arranged in the direction from the central electrode to the edge of the stretchable substrate; wherein,
the center electrode is used for providing a first voltage for one end of the comb-shaped electrode;
the peripheral electrode is used for providing a second voltage for the other end of the comb-shaped electrode;
the spring structure is used for generating deformation so as to change the distances between the centers of the sparse apertures and the centers of the stretchable substrates;
the comb-shaped electrode is used for generating electrostatic force so as to deform the spring structure.
4. A reconfigurable sparse aperture based zoom superlens according to claim 3, wherein the spring structure, the sparse aperture and the comb electrode are suspended by a pulling force between the spring structure and the central electrode, and a pulling force between the comb electrode and the peripheral electrode.
5. The reconfigurable sparse aperture based zoom superlens of claim 1, wherein the shape of the sparse aperture comprises a first regular shape comprising any one or more of a sector, a circle, or a rectangle.
6. The reconfigurable sparse aperture based zoom superlens of claim 1, wherein a number of the sparse apertures are symmetrical about a center of the stretchable substrate or about a line passing through a center of the stretchable substrate.
7. The reconfigurable sparse aperture based zoom superlens of claim 1, wherein a number of the sparse apertures comprise a number of focusing elements; symmetry exists for sparse apertures in the same focusing element.
8. The reconfigurable sparse aperture based zoom superlens of claim 1, wherein the sparse aperture further comprises a rigid substrate on which etching is performed to form the phase structure; the cross-sectional shape of the phase structure includes a second regular pattern including a T-shape or a circle shape.
9. A method for preparing a zoom superlens based on reconfigurable sparse aperture, which is applied to the zoom superlens as claimed in claim 1, comprising:
pretreating a substrate;
preparing a plurality of layer bonding layers and the stretchable substrate on the pretreated substrate; the method comprises the steps of carrying out a first treatment on the surface of the
Preparing the sparse aperture layer at a preset position, and preparing the sparse aperture in the sparse aperture layer;
and removing the substrate and the bonding layer corresponding to the substrate.
10. The method of manufacturing a reconfigurable sparse aperture based zoom superlens of claim 9, wherein when the stretchable substrate comprises the center electrode, the number of spring structures, the number of comb electrodes, and the number of peripheral electrodes, the method of manufacturing comprises:
preparing a protective layer, the bonding layer and the sparse aperture layer on the substrate in sequence;
preparing the sparse aperture, the spring structure and the comb structure in the sparse aperture layer;
preparing the comb-shaped electrode on the comb-tooth structure;
and removing part of the substrate and part of the bonding layer so as to suspend the sparse aperture, the spring structure and the comb-shaped electrode.
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