CN114709622B - Polarization unit based on super-surface structure, polarization converter and preparation method - Google Patents

Polarization unit based on super-surface structure, polarization converter and preparation method Download PDF

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CN114709622B
CN114709622B CN202210331430.6A CN202210331430A CN114709622B CN 114709622 B CN114709622 B CN 114709622B CN 202210331430 A CN202210331430 A CN 202210331430A CN 114709622 B CN114709622 B CN 114709622B
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structure layer
metal
polarization
metal structure
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CN114709622A (en
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潘武
李永瑞
张彬
李海珠
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Chongqing University of Post and Telecommunications
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Chongqing University of Post and Telecommunications
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
    • H01Q15/0086—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices having materials with a synthesized negative refractive index, e.g. metamaterials or left-handed materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/165—Auxiliary devices for rotating the plane of polarisation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P11/00—Apparatus or processes specially adapted for manufacturing waveguides or resonators, lines, or other devices of the waveguide type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/24—Polarising devices; Polarisation filters 
    • H01Q15/242—Polarisation converters
    • H01Q15/246—Polarisation converters rotating the plane of polarisation of a linear polarised wave
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/24—Polarising devices; Polarisation filters 
    • H01Q15/242—Polarisation converters
    • H01Q15/246—Polarisation converters rotating the plane of polarisation of a linear polarised wave
    • H01Q15/248—Polarisation converters rotating the plane of polarisation of a linear polarised wave using a reflecting surface, e.g. twist reflector
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
    • H05K3/022—Processes for manufacturing precursors of printed circuits, i.e. copper-clad substrates
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
    • H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
    • H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
    • H05K3/061—Etching masks
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
    • H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
    • H05K3/068—Apparatus for etching printed circuits
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Polarising Elements (AREA)

Abstract

The invention discloses a polarization unit based on a super-surface structure, a polarization converter and a preparation method, relates to the field of polarization converters, and solves the problem that the existing polarization converter can only realize perfect polarization conversion on a narrow band (the relative bandwidth is less than 1%) or a single frequency point, and the technical scheme is as follows: the dual-band polarization conversion device comprises a dielectric layer, a metal conversion layer plated on the front surface of the dielectric layer and used for realizing dual-band polarization conversion, and a metal reflection layer positioned on the back surface of the dielectric layer; the metal conversion layer comprises a first metal structure layer and a second metal structure layer, the first metal structure layer is nested in the second metal structure layer, the first metal structure layer is cross-shaped, the second metal structure layer is cross-shaped, the distance between the second metal structure layer and the first metal structure layer is equal, and the symmetrical axes of the first metal structure layer and the second metal structure layer are diagonal lines of the dielectric layer. The invention realizes the polarization conversion rate of terahertz double frequency bands and improves the relative bandwidth.

Description

Polarization unit based on super-surface structure, polarization converter and preparation method
Technical Field
The invention relates to the field of polarization converters, in particular to a polarization unit based on a super-surface structure, a polarization converter and a preparation method.
Background
Terahertz (Terahertz, THz) waves refer to electromagnetic waves having a frequency range of 0.1 to 10 THz. The long wave band of THz coincides with microwave, and the short wave band coincides with infrared wave, and compared with electromagnetic wave of other wave bands, terahertz has wide application prospect in fields such as biomedicine, security inspection, communication application and the like due to the position specificity. Polarization is an important feature of electromagnetic waves, which is described as the vibrational behavior of the electric field vector during transmission of electromagnetic waves, which plays an important role in terahertz wave transmission. The polarization conversion in the process of terahertz wave transmission and reflection can well avoid various external interferences in the transmission process.
The two-dimensional equivalent of the super surface as the metamaterial is a periodic sub-wavelength artificial electromagnetic medium, and has wide application in terahertz polarization conversion devices due to the negative refractive index, electromagnetic induction-like transparent effect, nonlinear effect and the like. In 2014, wen X et al designed a double-split-ring reflective super-surface polarization converter to achieve 0.44-0.76 THz cross-line polarization conversion and obtain higher polarization conversion efficiency. In 2018, pan W et al designed a split ring resonator and a hollow disk reflective polarization transformer to achieve a polarization conversion ratio of over 80% over the 0.584-1.352THz band. With research on polarization converters, single-frequency point and single-frequency band polarization converters cannot meet many application scenes, so the research direction is gradually directed to the research of dual-frequency/multi-frequency polarization converters. In 2016, su H et al designed a double-opening square-ring reflective polarization conversion device with a polarization conversion rate close to 100% at two independent frequency points of 0.348THz and 0.640THz, and achieved perfect polarization conversion. In 2020 Bilal R et al achieved perfect polarization conversion at two frequency points 1.10THz and 2.13 THz. The terahertz polarization converter achieves good polarization conversion effects, but the existing terahertz dual-frequency/multi-frequency polarization conversion device can achieve perfect polarization conversion only on a narrow band (the relative bandwidth is smaller than 1%) or a single frequency point, can not achieve perfect polarization conversion on a relatively large bandwidth and multi-frequency points, and limits application of the terahertz dual-channel polarization converter in terahertz dual-channel communication, imaging and detection.
Disclosure of Invention
The invention solves the problem that the existing polarization converter can only realize perfect polarization conversion on a narrow band (the relative bandwidth is less than 1%) or a single frequency point, and aims to provide a polarization unit based on a super-surface structure, a polarization converter and a preparation method. The metal conversion layer of the polarization unit provided by the invention adopts a classical anisotropic cross structure, so that components in two perpendicular directions can generate phase difference conditions meeting the cross polarization conversion when linear polarized waves are incident; because the metal structures with different sizes can generate resonance at different frequencies, and the coupling of the metal structures with different sizes can increase the resonance bandwidth, the metal conversion layer adopts a mode of combining the second metal structure layer (a nested structure) with the first metal structure layer (a cross structure) to realize the cross polarization conversion of double frequency bands. The invention further provides a preparation method based on the polarization converter, so that the processing of the polarization converter is realized.
The technical aim of the invention is realized by the following technical scheme:
in a first aspect, a polarization unit based on a super-surface structure is provided, including a dielectric layer, a metal conversion layer plated on the front surface of the dielectric layer for implementing dual-band polarization conversion, and a metal reflection layer positioned on the back surface of the dielectric layer;
The metal conversion layer comprises a first metal structure layer and a second metal structure layer, the first metal structure layer is nested in the second metal structure layer, the first metal structure layer is cross-shaped, the second metal structure layer is cross-shaped, the distance between the second metal structure layer and the first metal structure layer is equal, and the symmetrical axes of the first metal structure layer and the second metal structure layer are diagonal lines of the dielectric layer.
Further, the material of the metal conversion layer is any one of gold, silver, aluminum and copper.
Further, the dielectric layer is made of any one of polyimide, silicon and quartz.
Further, the period length of the polarization unit is 110-130 μm, the thickness of the dielectric layer is 30-60 μm, and the thicknesses of the metal conversion layer and the metal reflection layer are 100-300 nm.
Further, the first metal structure layer comprises a first long rectangle inclined by 45 degrees along an x-axis or a y-axis and a first short rectangle inclined by 45 degrees along the x-axis or the y-axis, and the first long rectangle and the first short rectangle are perpendicular to each other and are mutually bisected;
The length of the first long rectangle is 100-120 mu m, and the width is 24-28 mu m;
the first short rectangle has a length of 40 μm to 80 μm and a width of 24 μm to 28 μm.
Further, the second metal structure layer comprises a first cross-shaped structure layer and a twenty-first structure layer;
the first cross-shaped structural layer comprises a second long rectangle inclined by 45 degrees along the x axis or the y axis and a second short rectangle inclined by 45 degrees along the x axis or the y axis, and the second long rectangle and the second short rectangle are mutually perpendicular and mutually bisected;
The second structure layer comprises a second long rectangle inclined by 45 degrees along the x axis or the y axis and a second short rectangle inclined by 45 degrees along the x axis or the y axis, and the second long rectangle and the second short rectangle are perpendicular to each other and are mutually bisected;
The first cross-shaped structure layer is positioned in the twenty-first structure layer, and the area of the second metal structure layer on the medium layer is determined by subtracting the area of the first cross-shaped structure layer on the medium layer from the area of the twenty-first structure layer on the medium layer.
Further, a distance between the second long rectangle and the first metal structure layer in the length direction is 4-7 μm, a distance between the second long rectangle and the first metal structure layer in the width direction is 1-3 μm, a distance between the second short rectangle and the first metal structure layer in the length direction is 9-11 μm, and a distance between the second short rectangle and the first metal structure layer in the width direction is 1-3 μm;
the distance between the width boundary of the third long rectangle and the first metal structure layer is 9-11 mu m, and the distance between the width boundary of the third short rectangle and the first metal structure layer is 4-6 mu m.
Further, the distance between the second cross-shaped structural layer and the first cross-shaped structural layer in the length direction is equal, and the distance between the second cross-shaped structural layer and the first cross-shaped structural layer in the width direction is equal.
In a second aspect, a dual-band polarization converter based on a super-surface structure is provided, which includes a polarization unit according to the first aspect, and a plurality of the polarization units are periodically arranged on a plane perpendicular to the incidence plane of terahertz waves to form the dual-band polarization converter.
In a third aspect, a method for preparing a dual-band polarization converter based on a super-surface structure is provided, including a dual-band polarization converter based on a super-surface structure according to the second aspect, including:
Step one, cleaning a photoetching mask plate: firstly, placing the photoetching mask plate into an ultrasonic cleaner containing acetone for cleaning, then placing the ultrasonic cleaner into absolute ethyl alcohol for soaking, using deionized water for cleaning the photoetching mask plate, and finally using a nitrogen gun for blow-drying the photoetching mask plate;
Step two, cleaning a dielectric layer: cleaning the dielectric layer by using acetone and alcohol;
Thirdly, gold plating: plating gold with the thickness of 300nm and titanium with the thickness of 10nm on two sides of the dielectric layer film by utilizing a magnetron sputtering machine;
Fourth, gluing and pre-baking: firstly, placing the gold-plated photoetching mask plate on a photoresist homogenizing machine for photoresist homogenizing, and then, pre-baking the photoresist mask plate after photoresist homogenizing;
fifth, exposure and development: exposing and photoetching the photomask by using a photoetching machine, and then developing the photomask by using a developing solution;
sixth, etching: etching the gold-plated layer with the thickness of 300nm by using an ion beam etching machine to obtain a metal conversion layer;
seventh, photoresist removing: and immersing the etched photoetching mask plate in an acetone solution, removing photoresist on the surface of the photoetching mask plate by using a plasma photoresist remover, and finally cleaning the photoetching mask plate by using deionized water and air-drying.
Compared with the prior art, the invention has the following beneficial effects:
1. The metal conversion layer of the polarization unit provided by the invention adopts a classical anisotropic cross structure, so that components in two perpendicular directions can generate phase difference conditions meeting the cross polarization conversion when linear polarized waves are incident; because the metal structures with different sizes can generate resonance at different frequencies, and the coupling of the metal structures with different sizes can increase the resonance bandwidth, the metal conversion layer adopts a mode of combining a second metal structure layer (a nested structure) with a first metal structure layer (a cross structure) to realize the cross polarization conversion of double frequency bands, and the dielectric layer and the metal reflection layer of the polarization unit are realized by adopting the existing mature design scheme. The polarization converter provided by the invention is formed by periodically arranging a plurality of polarization units on the incidence plane perpendicular to the terahertz wave, so that the polarization converter is of a symmetrical structure, has the same polarization conversion function on y-incident ray polarized waves and x-incident ray polarized waves, can achieve more than 90% of polarization conversion rate in two frequency bands of 0.626-0.775THz and 1.324-1.369THz (the relative bandwidth respectively achieves 13% and 2%, and achieves perfect linear polarization conversion in two frequency bands of 0.642-0.739THz and 1.336-1.365THz (the relative bandwidth achieves 21% and 3%).
2. The nested cross-shaped super-surface metal conversion layer is easy to integrate and convenient to process.
3. The polarization converter provided by the invention can independently control the positions of the two frequency bands by adjusting different parameters, thereby meeting the application of various scenes.
4. The polarization converter provided by the invention has a symmetrical structure, and can generate the same polarization conversion effect on x and y polarized waves.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:
FIG. 1 is a schematic diagram of a polarization unit according to a first embodiment of the present invention;
FIG. 2 is a schematic diagram of a polarization unit according to an embodiment of the present invention;
FIG. 3 is a graph showing the spectral variation of the cross polarization conversion coefficient and co-polarization conversion coefficient of the polarization unit according to the embodiment of the present invention;
FIG. 4 is a spectrum variation curve of polarization conversion rate of a polarization unit according to an embodiment of the present invention;
Fig. 5 is a schematic structural diagram of a polarization converter formed by periodically arranging a plurality of polarization units according to an embodiment of the present invention.
In the drawings, the reference numerals and corresponding part names:
1. a dielectric layer; 2. a metal reflective layer; 3. a first metal structural layer; 4. and a second metal structure layer.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present invention and the descriptions thereof are for illustrating the present invention only and are not to be construed as limiting the present invention.
It should be appreciated that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
Embodiment one:
The terahertz polarization converter in the prior art realizes a good polarization conversion effect, but the existing terahertz dual-frequency/multi-frequency polarization conversion device can only realize perfect polarization conversion on a narrow band (the relative bandwidth is less than 1%) or a single frequency point, can not realize perfect polarization conversion on a relatively large bandwidth and a multi-frequency point, and limits the application of the polarization converter in terahertz dual-channel communication, imaging and detection. Therefore, the first embodiment provides a polarization unit based on a super-surface structure, so that the polarization converter can realize perfect polarization conversion at a relatively large bandwidth and multiple frequency points.
As shown in fig. 1, the first embodiment provides a polarization unit based on a super-surface structure, which includes a dielectric layer 1, a metal conversion layer plated on the front surface of the dielectric layer 1 for implementing dual-band polarization conversion, and a metal reflection layer 2 located on the back surface of the dielectric layer 1;
The metal conversion layer comprises a first metal structure layer 3 and a second metal structure layer 4, the first metal structure layer 3 is nested in the second metal structure layer 4, the first metal structure layer 3 is in a cross shape, the second metal structure layer 4 is in a cross shape, the distance between the second metal structure layer 4 and the first metal structure layer 3 is equal, and the symmetrical axes of the first metal structure layer 3 and the second metal structure layer 4 are diagonal lines of the medium layer 1.
Specifically, as shown in fig. 1, the first metal structure layer 3 is located in the second metal structure layer 4, the first metal structure layer 3 is in a cross structure in the middle, and the second metal structure layer 4 is in a black part in fig. 1, so that the first metal structure layer 3 is nested in the second metal structure layer 4, and the symmetry axes of the first metal structure layer 3 and the second metal structure layer 4 are diagonal lines of the dielectric layer 1, so that components in two perpendicular directions of a linearly polarized wave can generate phase difference conditions meeting cross polarization conversion during incidence.
In yet another embodiment of the present embodiment, the material of the metal conversion layer is any one of gold, silver, aluminum and copper.
Specifically, when the material of the metal conversion layer is gold, its electrical conductivity is 4.561 ×107S/m, and when it is one of silver, aluminum and copper, its electrical conductivity is common knowledge, and thus it is not described.
In yet another embodiment of the present embodiment, the material of the dielectric layer 1 is any one of polyimide, silicon and quartz.
Specifically, the dielectric layer 1 has a dielectric constant of 3.4 when it is polyimide, and has a dielectric constant of common knowledge when it is one of silicon and quartz, and thus is not described.
In yet another embodiment of the present embodiment, the period length of the polarization unit is 110 μm to 130 μm, the thickness of the dielectric layer 1 is 30 μm to 60 μm, and the thicknesses of the metal conversion layer and the metal reflection layer 2 are 100nm to 300nm.
Specifically, as shown in fig. 2, the period length of one polarization unit may be any length value in the range of 110 μm to 130 μm, for example, the thickness h=50 μm of the dielectric layer 1, the period length of the polarization unit may be p=120 μm by 120 μm, and the thicknesses of the metal conversion layer and the metal reflection layer 2 are 300nm. The material of the metal reflecting layer 2 is gold, the thickness of which is 0.3 μm, and the electrical conductivity of which is 4.561 X107S/m.
In yet another embodiment of the present embodiment, the first metal structure layer 3 includes a first long rectangle inclined by 45 degrees along the x-axis or the y-axis and a first short rectangle inclined by 45 degrees along the x-axis or the y-axis, and the first long rectangle and the first short rectangle are perpendicular to each other and bisected with each other;
The length of the first long rectangle is 100-120 mu m, and the width is 24-28 mu m;
the first short rectangle has a length of 40 μm to 80 μm and a width of 24 μm to 28 μm.
In yet another embodiment of the present embodiment, the second metal structure layer 4 includes a first cross-shaped structure layer and a twentieth-shaped structure layer;
the first cross-shaped structural layer comprises a second long rectangle inclined by 45 degrees along the x axis or the y axis and a second short rectangle inclined by 45 degrees along the x axis or the y axis, and the second long rectangle and the second short rectangle are mutually perpendicular and mutually bisected;
The second structure layer comprises a second long rectangle inclined by 45 degrees along the x axis or the y axis and a second short rectangle inclined by 45 degrees along the x axis or the y axis, and the second long rectangle and the second short rectangle are perpendicular to each other and are mutually bisected;
the first cross-shaped structural layer is located in the twenty-first structural layer, and the area of the twenty-first structural layer on the medium layer 1 is subtracted by the area of the first cross-shaped structural layer on the medium layer 1 to determine the area of the second metal structural layer 4 on the medium layer 1.
In yet another embodiment of the present invention, a distance between the second long rectangle and the first metal structure layer in the longitudinal direction is 4 μm to 7 μm, a distance between the second long rectangle and the first metal structure layer in the width direction is 1 μm to 3 μm, a distance between the second short rectangle and the first metal structure layer in the longitudinal direction is 9 μm to 11 μm, and a distance between the second short rectangle and the first metal structure layer in the width direction is 1 μm to 3 μm;
the distance between the width boundary of the third long rectangle and the first metal structure layer is 9-11 mu m, and the distance between the width boundary of the third short rectangle and the first metal structure layer is 4-6 mu m.
In yet another embodiment of the present invention, the distance between the second cross-shaped structural layer and the first cross-shaped structural layer in the longitudinal direction is equal, and the distance between the second cross-shaped structural layer and the first cross-shaped structural layer in the width direction is equal.
In order to achieve a better dual-frequency terahertz polarization conversion effect, considering the design scheme of multi-frequency resonance of the super surface, the following solutions are mainly available: the design scheme of the nested structure is considered because the design of the stacked structure, the multi-parting structure, the resonator combined structure with different shapes, the nested structure and the like are complex in pattern, and certain difficulties are brought to the design and the preparation of the device. For realizing polarization conversion effect, there are usually two structures, namely a chiral structure and an anisotropic structure, for realizing polarization conversion, the chiral structure has certain difficulty in design and preparation due to asymmetry, so that the anisotropic structure is adopted. The metal conversion layer designed through the nested structure and the anisotropic structure has the beneficial effects of simple structure and easy control of parameters in all directions. According to the invention, by combining the anisotropic structure with the nested structure, due to the capacitive coupling effect between structures with different sizes, which is brought by the nested structure, the polarization conversion frequency band can be expanded, and the structure is simple, so that the design and the preparation are easy.
In this embodiment, a parameter is selected in the length range to demonstrate the technical effect that the polarization unit provided by the present invention can achieve, as shown in fig. 2, specific parameters of the first metal structure layer 3 and the second metal structure layer 4 of the metal conversion layer are: l=50.0 μm, w=30.0 μm, a=35.0 μm, b=26 μm, c=5 μm, m=10 μm, n=15 μm. Wherein l represents half of the length of the first long rectangle, w represents half of the length of the first short rectangle, a represents the widths of the third long rectangle and the third short rectangle, b represents the widths of the second long rectangle and the second short rectangle, c represents the distance between the third long rectangle and the second long rectangle in the width direction, n represents the distance between the third short rectangle and the first short rectangle in the width direction, and m represents the distance between the third long rectangle and the first long rectangle in the width direction.
When the x-ray polarized terahertz wave is perpendicularly incident on the surface of the polarization unit along the-z axis direction, the co-polarization coefficient of the polarization unit is denoted as r xx＝Erx/Eix, and the cross-polarization coefficient r yx＝Ery/Eix, wherein x in r yx represents the polarization direction of the incident electromagnetic wave, and y represents the polarization direction of the reflected electromagnetic wave. E ix represents the energy amplitude of the x-polarized incident wave, E rx represents the energy amplitude of the x-polarized wave reflected by the super surface, and E ry represents the energy amplitude of the y-polarized reflected wave. The structure of the polarized cell was simulated with commercial simulation software CST MICROWAVE STUDIO 2020.
As shown in fig. 3, when the x-polarized wave is vertically incident along the-z axis direction, the cross reflection coefficient ryx obtained by observing the S21 parameter in the simulation software reaches more than 0.8 in two frequency bands of 0.642-0.785 THz and 1.325-1.362 THz respectively, and the co-polarized reflection coefficient r xx obtained by observing the S22 parameter is lower than 0.2, that is, most of the energy of the incident x-polarized wave is converted into the energy of y-polarized wave in the two frequency bands.
The linear polarization conversion rate is defined by the cross polarization coefficient and co-polarization coefficient
As shown in FIG. 4, the polarization conversion rate of the polarization unit reaches over 90% in two frequency bands of 0.626-0.775 THz and 1.324-1.369 THz, and the polarization conversion rate is close to 100% in two frequency bands of 0.642-0.739 THz and 1.336-1.365 THz, so that perfect linear polarization conversion is realized.
According to the data obtained in fig. 4, the invention uses a relative bandwidth calculation formula f=2× (f h-fl)/(fh+fl), wherein f h is the high-frequency band and f l is the low-frequency band, and according to the formula, the relative bandwidths of two frequency bands with the polarization conversion rate of more than 90% of the polarization unit reach 13% and 2% respectively, and the relative bandwidths of two frequency bands with the polarization conversion rate close to 100% reach 21% and 3%.
Based on the above discussion, the metal conversion layer of the polarization unit can generate different resonance effects on different components of the incident electromagnetic wave in different directions, so that phase difference conditions (180 DEG) and amplitude conditions meeting linear polarization conversion are generated on the components of the incident electromagnetic wave in two perpendicular directions, meanwhile, the distance between two metal cross structures ensures the capacitive coupling effect between the two structures, and on the basis of generating double frequency bands, the bandwidth of the two conversion frequency bands can be increased, thereby increasing the frequency band utilization rate, and the polarization unit can be better applied to the fields of double-channel communication, imaging and detection based on terahertz.
Embodiment two:
the second embodiment provides a dual-band polarization converter based on a super-surface structure, which comprises a polarization unit in the first embodiment, wherein a plurality of polarization units are periodically arranged on a plane perpendicular to the incidence plane of terahertz waves to form the dual-band polarization converter.
Specifically, since the size of one polarization unit is very small, the subsequent semiconductor preparation is very inconvenient, and therefore, a plurality of polarization units are periodically arranged on the incidence plane perpendicular to the terahertz waves to form a dual-band polarization converter, the polarization converter also has the polarization conversion rate of the polarization units in two frequency bands of 0.626-0.775 THz and 1.324-1.369 THz reaching more than 90%, and the polarization conversion rate in two frequency bands of 0.642-0.739 THz and 1.336-1.365 THz approaching to 100%, so that the perfect linear polarization conversion effect is realized.
The relative bandwidths of the two frequency bands reach 13% and 2% respectively when the polarization conversion rate of the terahertz dual-band reaches more than 90%, and reach 21% and 3% when the polarization conversion rate is close to 100%.
Embodiment III:
the third embodiment provides a preparation method of a dual-band polarization converter based on a super-surface structure, including a dual-band polarization converter based on a super-surface structure in the second embodiment, including:
Step one, cleaning a photoetching mask plate: firstly, placing the photoetching mask plate into an ultrasonic cleaner containing acetone for cleaning, then placing the ultrasonic cleaner into absolute ethyl alcohol for soaking, using deionized water for cleaning the photoetching mask plate, and finally using a nitrogen gun for blow-drying the photoetching mask plate;
Step two, cleaning a dielectric layer: cleaning the dielectric layer by using acetone and alcohol;
Thirdly, gold plating: plating gold with the thickness of 300nm and titanium with the thickness of 10nm on two sides of the dielectric layer film by utilizing a magnetron sputtering machine;
Fourth, gluing and pre-baking: firstly, placing the gold-plated photoetching mask plate on a photoresist homogenizing machine for photoresist homogenizing, and then, pre-baking the photoresist mask plate after photoresist homogenizing;
fifth, exposure and development: exposing and photoetching the photomask by using a photoetching machine, and then developing the photomask by using a developing solution;
sixth, etching: etching the gold-plated layer with the thickness of 300nm by using an ion beam etching machine to obtain a metal conversion layer;
seventh, photoresist removing: and immersing the etched photoetching mask plate in an acetone solution, removing photoresist on the surface of the photoetching mask plate by using a plasma photoresist remover, and finally cleaning the photoetching mask plate by using deionized water and air-drying.
Specifically, the photolithographic reticle is cleaned. And (3) placing the photoetching mask plate into an ultrasonic cleaner containing acetone for cleaning, removing surface magazines, then placing the mask plate into absolute ethyl alcohol for soaking, cleaning the mask plate by using deionized water, and finally drying by using a nitrogen gun.
And (5) cleaning the substrate. The polyimide substrate is cleaned in advance with acetone and alcohol, and the polyimide surface of the substrate is kept dry, with the purpose of ensuring Au plating uniformity and adhesion between the substrate and metal.
The dielectric layer is polyimide, and the polyimide film is gold-plated. Gold with a thickness of 300nm and titanium with a thickness of 10nm were plated on both sides of the polyimide film using a magnetron sputtering machine FHR, and titanium was added in order to increase adhesion between the metal and the polyimide. The thickness of the metal reflecting layer ensures that electromagnetic waves can be totally reflected at the bottom layer, so that the polarization conversion efficiency is improved, the titanium layer ensures good adhesiveness between the metal layer and the dielectric layer, the polarization conversion effect is not affected, the area reaches 120 micrometers by 120 micrometers, and the working frequency band of the device is ensured to be positioned on 0.1-2 THz.
Gluing and pre-baking. And placing the sample on a spin coater for spin coating, and then pre-baking the spin coated sample.
And (5) exposing and developing. The sample is subjected to exposure lithography by using a lithography machine, and then developed by using a developing solution.
Etching. And etching the gold-plated layer with the thickness of 300nm by using an ion beam etching machine. The thickness of the obtained metal conversion layer is 300nm, so that electromagnetic waves can resonate in the metal conversion layer, and a polarization conversion effect is generated.
And (5) removing photoresist. And immersing the etched sample in an acetone solution, removing a photoetching machine on the surface of the sample by using a plasma photoresist remover, and finally cleaning the sample by using deionized water and air-drying.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (9)

1. The polarization unit based on the super-surface structure is characterized by comprising a dielectric layer (1), a metal conversion layer plated on the front surface of the dielectric layer (1) for realizing dual-band polarization conversion, and a metal reflection layer (2) positioned on the back surface of the dielectric layer (1);
The metal conversion layer comprises a first metal structure layer (3) and a second metal structure layer (4), the first metal structure layer (3) is nested in the second metal structure layer (4), the first metal structure layer (3) is in a cross shape, the second metal structure layer (4) is in a cross shape, the distance between the second metal structure layer (4) and the first metal structure layer (3) is equal, and the symmetry axes of the first metal structure layer (3) and the second metal structure layer (4) are diagonal lines of the dielectric layer (1);
wherein the first metal structure layer (3) comprises a first long rectangle inclined by 45 degrees along an x-axis or a y-axis and a first short rectangle inclined by 45 degrees along the x-axis or the y-axis, and the first long rectangle and the first short rectangle are mutually perpendicular and mutually bisected;
Wherein the second metal structure layer (4) comprises a first cross-shaped structure layer and a twenty-first structure layer; the first cross-shaped structural layer comprises a second long rectangle inclined by 45 degrees along the x axis or the y axis and a second short rectangle inclined by 45 degrees along the x axis or the y axis, and the second long rectangle and the second short rectangle are mutually perpendicular and mutually bisected; the second structure layer comprises a second long rectangle inclined by 45 degrees along the x axis or the y axis and a second short rectangle inclined by 45 degrees along the x axis or the y axis, and the second long rectangle and the second short rectangle are perpendicular to each other and are mutually bisected; the first cross-shaped structure layer is positioned in the twenty-first structure layer, and the area of the twenty-first structure layer on the medium layer (1) is subtracted by the area of the first cross-shaped structure layer on the medium layer (1) to determine the area of the second metal structure layer (4) on the medium layer (1).
2. The super surface structure based polarization unit according to claim 1, wherein the material of the metal conversion layer is any one of gold, silver, aluminum and copper.
3. A polarization cell based on a super surface structure according to claim 1, characterized in that the material of the dielectric layer (1) is any one of polyimide, silicon and quartz.
4. The polarization unit based on the super-surface structure according to claim 1, wherein the period length of the polarization unit is 110-130 μm, the thickness of the dielectric layer (1) is 30-60 μm, and the thicknesses of the metal conversion layer and the metal reflection layer (2) are 100-nm-300 nm.
5. The super-surface structure-based polarization unit according to claim 1, wherein the length of the first long rectangle is 100 μm to 120 μm, and the width is 24 μm to 28 μm;
The length of the first short rectangle is 40-80 mu m, and the width of the first short rectangle is 24-28 mu m.
6. The super-surface structure-based polarization unit according to claim 1, wherein a distance in a length direction of the second long rectangle from a length direction of the first metal structure layer (3) is 4 μm to 7 μm, a distance in a width direction of the second long rectangle from a width direction of the first metal structure layer (3) is 1 μm to 3 μm, a distance in a length direction of the second short rectangle from a length direction of the first metal structure layer (3) is 9 μm to 11 μm, and a distance in a width direction of the second short rectangle from a width direction of the first metal structure layer (3) is 1 μm to 3 μm;
The distance between the width boundary of the third long rectangle and the first metal structure layer (3) is 9-11 microns, and the distance between the width boundary of the third short rectangle and the first metal structure layer (3) is 4-6 microns.
7. The super surface structure based polarization unit according to claim 6, wherein the distance between the second cross-shaped structure layer and the first cross-shaped structure layer in the longitudinal direction is equal, and the distance between the second cross-shaped structure layer and the first cross-shaped structure layer in the width direction is equal.
8. A dual-band polarization transformer based on a super-surface structure, comprising a polarization unit according to any one of claims 1 to 7, characterized in that a plurality of said polarization units are periodically arranged on a plane perpendicular to the incidence plane of terahertz waves to constitute said dual-band polarization transformer.
9. A method for manufacturing a super-surface structure based dual-band polarization transformer, comprising the super-surface structure based dual-band polarization transformer according to claim 8, comprising:
Step one, cleaning a photoetching mask plate: firstly, placing the photoetching mask plate into an ultrasonic cleaner containing acetone for cleaning, then placing the ultrasonic cleaner into absolute ethyl alcohol for soaking, using deionized water for cleaning the photoetching mask plate, and finally using a nitrogen gun for blow-drying the photoetching mask plate;
Step two, cleaning a dielectric layer: cleaning the dielectric layer by using acetone and alcohol;
Thirdly, gold plating: plating gold with the thickness of 300nm and titanium with the thickness of 10nm on two sides of the dielectric layer film by utilizing a magnetron sputtering machine;
Fourth, gluing and pre-baking: firstly, placing the gold-plated photoetching mask plate on a photoresist homogenizing machine for photoresist homogenizing, and then, pre-baking the photoresist mask plate after photoresist homogenizing;
fifth, exposure and development: exposing and photoetching the photomask by using a photoetching machine, and then developing the photomask by using a developing solution;
sixth, etching: etching the gold-plated layer with the thickness of 300nm by using an ion beam etching machine to obtain a metal conversion layer;
seventh, photoresist removing: and immersing the etched photoetching mask plate in an acetone solution, removing photoresist on the surface of the photoetching mask plate by using a plasma photoresist remover, and finally cleaning the photoetching mask plate by using deionized water and air-drying.
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