CN111896479B - Terahertz chiral discrimination device and circular polarization selector - Google Patents

Terahertz chiral discrimination device and circular polarization selector Download PDF

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CN111896479B
CN111896479B CN202010930167.3A CN202010930167A CN111896479B CN 111896479 B CN111896479 B CN 111896479B CN 202010930167 A CN202010930167 A CN 202010930167A CN 111896479 B CN111896479 B CN 111896479B
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strip
metal
arm
terahertz
shaped metal
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CN111896479A (en
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亓丽梅
陶翔
杨君
刘紫玉
陈智娇
姚远
俞俊生
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Beijing University of Posts and Telecommunications
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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    • 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 
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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Abstract

The invention provides a terahertz chiral discrimination device and a circular polarization selector, wherein the device comprises: a metal layer; the dielectric layer is positioned on one side of the metal layer; the metal pattern layer is positioned on one side of the dielectric layer, which is far away from the metal layer, and comprises metal pattern units which are periodically arranged; the metal pattern unit comprises a set metal pattern, the set metal pattern comprises a strip-shaped metal main body, a first strip-shaped metal arm and a second strip-shaped metal arm, the first strip-shaped metal arm is a structure extending from the first end of the strip-shaped metal main body along a first direction perpendicular to the strip-shaped metal main body, and one end of the second strip-shaped metal arm is vertically connected with the strip-shaped metal main body; the first strip-shaped metal arm and the second strip-shaped metal arm are located on the same side of the strip-shaped metal main body. By the scheme, different absorption intensities of different circularly polarized waves can be achieved, and therefore the purpose of identifying a hand sample or selecting the circularly polarized waves in the terahertz waveband can be achieved.

Description

Terahertz chiral discrimination device and circular polarization selector
Technical Field
The invention relates to the technical field of terahertz devices, in particular to a terahertz chiral identification device and a circular polarization selector.
Background
Terahertz (THz) waves refer to electromagnetic waves with a frequency range of 0.1 to 10THz, and are between infrared and microwave in the electromagnetic spectrum. The energy corresponding to 1THz is only about 4.14meV, which is far lower than visible light and ultraviolet rays, is one part in millions of X rays, does not generate ionization to biological molecules, and greatly reduces the damage caused by radiation to tissues and organs in an organism. Compared with an optical waveband, the interaction between the terahertz wave and the material relates to the rotation and vibration energy levels of biological macromolecules, and the relevance between the corresponding terahertz electromagnetic response and the overall molecular structure is higher. Therefore, theoretically, the circular dichroism for measuring the polarization response of the terahertz waveband chiral molecules is expected to be an effective means for identifying biological macromolecules and understanding the molecular activity and the interaction between molecules. However, the strong absorption of water in the terahertz frequency band and the lack of a high-performance terahertz polarization device greatly limit the measurement of circular dichroism in a physiological environment for natural chiral substances.
In addition, theoretically, the identification of different chiral molecules and enantiomers can be realized by utilizing a structure with circular dichroism characteristics in a terahertz waveband, but people find in simulation that a strong circular dichroism characteristic can be generated by utilizing a three-dimensional spiral structure or a metal structure with a metal column connected in the middle in the terahertz waveband, but the structures are complex to prepare in the terahertz waveband and are not beneficial to practical application, and the traditional two-dimensional super surface is a flat plate structure and is easy to prepare, but a circular dichroism signal generated by the structure is weak and is not beneficial to the detection of chiral molecules.
In addition, in terahertz communication, that is, in current 6G communication, the circular polarization selector in the prior art can selectively absorb an incident circular polarization wave, but an optical path discrimination system generally composed of a quarter-wave plate and a linear polarizer is complicated, and thus is inconvenient to use in practice.
Disclosure of Invention
In view of this, the embodiment of the invention provides a terahertz chiral discrimination device and a circular polarization selector, which can achieve the purpose of discriminating a chiral sample in a terahertz waveband and utilize the absorption difference of the discriminator on left-handed and right-handed circular polarization waves, and can be simultaneously applied to the terahertz circular polarization selector.
In order to achieve the purpose, the invention is realized by adopting the following scheme:
according to an aspect of an embodiment of the present invention, there is provided a terahertz chiral discrimination device, including:
a metal layer;
the dielectric layer is positioned on one side of the metal layer;
the metal pattern layer is positioned on one side of the dielectric layer, which is far away from the metal layer, and comprises metal pattern units which are periodically arranged; the metal pattern unit comprises a set metal pattern, the set metal pattern comprises a strip-shaped metal main body, a first strip-shaped metal arm and a second strip-shaped metal arm, the first strip-shaped metal arm is a structure extending from the first end of the strip-shaped metal main body along a first direction perpendicular to the strip-shaped metal main body, and one end of the second strip-shaped metal arm is vertically connected with the strip-shaped metal main body; the first strip-shaped metal arm and the second strip-shaped metal arm are located on the same side of the strip-shaped metal main body.
In some embodiments, the terahertz chiral discrimination device further includes: a third strip-shaped metal arm; the third strip-shaped metal arm is a structure extending from the second end of the strip-shaped metal body in a second direction perpendicular to the strip-shaped metal body; the first direction is opposite to the second direction.
In some embodiments, the third strip metal arm is shorter in length than the first strip metal arm and longer than the second strip metal arm.
In some embodiments, the first direction is a direction that enables the strip metal body, the first strip metal arm, and the second strip metal arm to form an F-shape, or the first direction is a direction that enables the strip metal body, the first strip metal arm, and the second strip metal arm to form an F-shape mirror image.
In some embodiments, the metal layer and the metal pattern layer are made of gold, aluminum, or copper; the material used for the dielectric layer comprises polyimide, silicon dioxide or silicon.
In some embodiments, the length and width of the strip-shaped metal body range from 5 μm to 900 μm and from 10 μm to 500 μm, respectively; the length range of the long side of the first strip-shaped metal arm is 10-900 mu m; the length range of the long side of the second strip-shaped metal arm is 10-900 mu m; the length and width of the third strip-shaped metal arm are respectively 10-900 μm and 10-500 μm.
In some embodiments, the metal pattern layer has a thickness ranging from 0.05 μm to 5 μm; the thickness range of the dielectric layer is 3-1000 μm; the thickness of the metal layer is not less than 0.05 μm; the thickness of the metal pattern layer is smaller than that of the dielectric layer, and the thickness of the metal pattern layer is smaller than that of the metal layer.
In some embodiments, the length of the sides of each metal pattern unit ranges from 50 μm to 1000 μm; the distance between each set metal pattern and each edge of the corresponding metal pattern unit is the same.
According to another aspect of the embodiments of the present invention, there is provided a circular polarization selector, including: a terahertz chiral discrimination device as described in the above embodiments.
According to the terahertz chiral discrimination device and the circular polarization selector, selective absorption can be performed on left-hand circular polarized waves or right-hand circular polarized waves through the terahertz chiral discrimination device. In addition, other structures can be introduced into the tail end of the metal pattern, so that the circular dichroism characteristic of the double-waveband is realized, and the identification range is wider. Meanwhile, the terahertz chiral discrimination device can be used for detecting terahertz chiral molecules and can also be applied to the aspect of circular polarization selectors.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It will be appreciated by those skilled in the art that the objects and advantages that can be achieved with the present invention are not limited to the specific details set forth above, and that these and other objects that can be achieved with the present invention will be more clearly understood from the detailed description that follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. For purposes of illustrating and describing some portions of the present invention, corresponding parts of the drawings may be exaggerated, i.e., may be larger, relative to other components in an exemplary apparatus actually manufactured according to the present invention. In the drawings:
fig. 1 is a schematic structural diagram of a terahertz chiral discrimination device according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a terahertz chiral discrimination device according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a first terahertz chiral discrimination device with a plurality of periodic units according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of absorption spectra of a left-handed and a right-handed circularly polarized waves of a first terahertz chiral discrimination device according to an embodiment of the present invention;
fig. 5 is a schematic diagram of an electric field distribution of a first terahertz chiral discrimination device at a maximum circular dichroism position according to an embodiment of the present invention;
FIG. 6 is a schematic structural diagram of a second terahertz chiral discrimination device with a plurality of periodic units according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of absorption spectra of left and right circularly polarized waves of a second terahertz chiral discrimination device according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of circular dichroism values corresponding to first and second terahertz chiral discrimination devices according to an embodiment of the present invention;
fig. 9 is a schematic structural diagram of a third terahertz chiral discrimination device according to an embodiment of the present invention;
FIG. 10 is a schematic structural diagram of a third terahertz chiral discrimination device with multiple periodic units according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of absorption spectra of left and right circularly polarized waves of a third terahertz chiral discrimination device according to an embodiment of the present invention;
FIG. 12 is a schematic diagram of the electric field distribution of a third terahertz chiral discrimination device at the first maximum circular dichroism position in accordance with an embodiment of the present invention;
FIG. 13 is a schematic diagram of the electric field distribution of a third terahertz chiral discrimination device at a second maximum circular dichroism position in accordance with an embodiment of the present invention;
fig. 14 is a schematic structural diagram of a fourth terahertz chiral discrimination device according to an embodiment of the present invention;
FIG. 15 is a schematic structural diagram of a fourth terahertz chiral discrimination device with multiple periodic units according to an embodiment of the present invention;
FIG. 16 is a schematic diagram of absorption spectra of left and right circularly polarized waves of a fourth terahertz chiral discrimination device according to an embodiment of the present invention;
fig. 17 is a schematic diagram of a circular dichroism curve of a fourth terahertz chiral discrimination device according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.
It should be emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, elements, steps or components, but does not preclude the presence or addition of one or more other features, elements, steps or components.
In the infrared and visible light bands, people use the electromagnetic coupling effect of the chiral super surface and chiral molecules to distinguish different chiral molecules. Based on the principle, in the terahertz wave band, the identification of different chiral molecules and enantiomers can be realized based on the circular dichroism characteristics of the metamaterial. In the prior art, strong circular dichroism is generated by utilizing a three-dimensional spiral structure or a metal structure connected with a metal column in the middle in a terahertz frequency band, but the structures are complex to prepare in the terahertz frequency band and are not beneficial to practical application, the traditional two-dimensional super surface is a flat plate structure and is easy to prepare, but the existing research shows that the generated circular dichroism signal is weak and effective identification of chiral molecules is not facilitated.
Fig. 1 is a schematic structural diagram of a terahertz chiral discrimination device according to an embodiment of the present invention, and as shown in fig. 1, the terahertz chiral discrimination device according to the embodiment includes a metal layer 100, a dielectric layer 200, and a metal pattern layer 300.
The terahertz wave can be divided into a left-handed circularly polarized wave, a right-handed circularly polarized wave, and the like. The super surface is a periodic structure which is artificially designed, local electromagnetic resonance response can be enhanced through reasonable design, and sub-wavelength resolution is realized. The super-surface-based biosensor can realize sub-wavelength resolution by enhancing local electromagnetic resonance, and greatly improve the resolution and sensitivity of the sensor.
The material used for the metal layer 100 may include gold, aluminum, or copper. For example, the metal layer is made of gold. In the process of using the device, terahertz waves pass through the metal pattern layer and the dielectric layer, and the metal layer needs to enable the waves not to penetrate through the metal pattern layer and the dielectric layer. Therefore, the thickness of the metal layer may range not less than 0.05 μm. For example, the thickness of the metal layer may be 0.5 μm, 20 μm, 100 μm, or the like. The metal layer may be a metal film, a metal plate, or the like.
The dielectric layer 200 is located at one side of the metal layer 100. The material used for the dielectric layer may include polyimide, silicon dioxide, silicon, or other materials. The dielectric layer is completely overlapped with one side of the metal layer. The shape of the dielectric layer may be square, rectangular or other shapes. In addition, the length range of a first side of one side, completely superposed with the metal layer, of the dielectric layer in each period is 50-1000 microns, and the length range of a second side adjacent to the first side is 50-1000 microns; wherein a length of the first side is equal to a length of the second side. For example, the dielectric layer is made of polyimide, which has a dielectric constant of 3.4 and a loss tangent of 0.008. When different dielectric materials are selected, a proper dielectric constant can be selected according to the frequency range required by the terahertz waves, and the dielectric materials are further selected based on the dielectric constant.
The first side may have a length of 160 μm and the second side 160 μm. The thickness of the dielectric layer ranges from 3 mu m to 1000 mu m. For example, the dielectric layer may have a thickness of 60 μm, 120 μm, 150 μm, or the like.
The metal pattern layer 300 is positioned on one side of the dielectric layer 200 far away from the metal layer 100 and comprises metal pattern units 310 which are arranged periodically; the metal pattern unit 310 includes a set metal pattern 311, the set metal pattern 311 includes a bar-shaped metal body 311a, a first bar-shaped metal arm 311b, and a second bar-shaped metal arm 311c, the first bar-shaped metal arm 311b is a structure extending from a first end of the bar-shaped metal body along a first direction perpendicular to the bar-shaped metal body, and one end of the second bar-shaped metal arm 311c is vertically connected to the bar-shaped metal body; the first strip-shaped metal arm 311b and the second strip-shaped metal arm 311c are located on the same side of the strip-shaped metal body 311 a.
Wherein the thickness range of the metal pattern layer is 0.05-5 mu m; for example, the thickness of the metal pattern layer is 2 μm, 3 μm, 2.8 μm. In addition, the thickness of the metal pattern layer is smaller than that of the dielectric layer, and the thickness of the metal pattern layer is smaller than that of the metal layer. The material used for the metal pattern layer may include gold, aluminum, or other metals such as copper. The side of the dielectric layer away from the metal layer means the side of the dielectric layer not in contact with the metal layer and the side opposite to the side in contact with the metal layer. The metal patterns are arranged in rows at the same pitch and in columns at the same pitch, thereby forming metal pattern units arranged periodically. It is contemplated that the metal pattern may include letters without excluding other patterns. The strip-shaped metal main body can be 5-900 μm long in length range and 10-500 μm wide in length range; for example, the strip-shaped metal body may be 40 μm, 70 μm, 86 μm, or the like in length; the width is 30 μm, 46 μm or 60 μm. The length range of the long side of the first strip-shaped metal arm can be 10-900 micrometers; for example, the length of the long side of the first bar-shaped metal arm may be 40 μm, 90 μm, 79 μm, or the like. The length range of the long side of the second strip-shaped metal arm can be 10-900 micrometers; for example, the length of the long side of the second strip-shaped metal arm may be 60 μm, 90 μm, 129 μm, or the like.
Furthermore, the length of the first strip-shaped metal arm can also be smaller than the length of the second strip-shaped metal arm. For example, the length of the first strip-shaped metal arm is 60 μm, and the length of the second strip-shaped metal arm is 80 μm. Or the length of the first strip-shaped metal arm may also be equal to the length of the second strip-shaped metal arm. For example, the length of the first strip-shaped metal arm is 60 μm, and the length of the second strip-shaped metal arm is 60 μm.
In some embodiments, the length of the sides of each metal pattern unit ranges from 50 μm to 1000 μm; the distance between each set metal pattern and each edge of the corresponding metal pattern unit is the same.
The shape of each metal pattern unit can be a square, a rectangle, a pentagon or other polygons. Also, the side of each metal pattern unit may be 63 μm, 72 μm, 80 μm, or the like. For example, the metal pattern unit may be square in shape, and the side length thereof may be 63 μm; the number of periods included in the metal pattern layer may be m × n, where m is greater than or equal to 10, and n is greater than or equal to 10. If each metal pattern unit is a pentagon or other polygons, the number of periods included in the metal pattern layer may be represented in other manners. The metal pattern units may be shaped so as to be closely connected together, and there is no space between the plurality of connected metal pattern units. Each set metal pattern is positioned in the central position of each corresponding metal pattern unit. If the metal pattern units are arranged periodically, the metal pattern layers are provided with a plurality of set metal patterns, and each set metal pattern corresponds to one metal pattern unit. Since each set metal pattern has an electrical resonance in the process of use, if the distance between two set metal patterns is too close, the two set metal patterns will interfere with each other in the process of identification, and the use effect of the device will be affected.
Illustratively, the material of the metal pattern layer is gold, and the conductivity of the gold is 4.56 x 107And (5) S/m. Assuming that the metal pattern is F-shaped, the width of the bar-shaped metal body is 23 μm, the length of the bar-shaped metal body is 106 μm, the length of the long side of the first bar-shaped metal arm is 61 μm, and the length of the long side of the second bar-shaped metal arm is 54 μm. The first strip-shaped metal arm and the second strip-shaped metal arm have a certain interval therebetween, and the interval can be 12 μm. The long side of the metal bar arm is calculated from the long side of the metal bar body closest to the metal bar arm, and the long side is defined as the bar from the long side to the end of the long side of the metal bar armThe length distance of the metal arms.
Fig. 2 is a schematic structural diagram of a terahertz chiral discrimination device according to an embodiment of the present invention. As shown in fig. 2, specifically, the material of the metal layer is gold, and the thickness thereof is 0.2 μm; the dielectric layer is made of polyimide, the dielectric constant of the polyimide is 3.4, the loss tangent of the polyimide is 0.008, the thickness d of the polyimide is 33 mu m, the length of the dielectric layer can be 160 mu m, and the width of the dielectric layer can be 160 mu m. The metal pattern layer is made of gold, the metal pattern layer is F-shaped, the thickness of the metal pattern layer is 0.2 mu m, the width w of the strip-shaped metal body of the metal pattern is 23 mu m, the length L of the strip-shaped metal body is 106 mu m, the length of the long side s1 of the first strip-shaped metal arm is 61 mu m, and the length of the long side s2 of the second strip-shaped metal arm is 54 mu m. The first strip-shaped metal arm and the second strip-shaped metal arm have a certain interval therebetween, and the interval m can be 12 μm. The terahertz chiral discrimination device is used as a first terahertz chiral discrimination device. The length and width of the dielectric layer are shown as that only one set metal pattern is included in the metal pattern layer on the dielectric layer, and if the metal pattern units are periodically arranged, all metals can be set according to the parameters of each metal pattern layer, the parameters of the dielectric layer and the parameters of the metal layer.
Fig. 3 is a schematic structural diagram of a first terahertz chiral discrimination device with a plurality of periodic units according to an embodiment of the present invention. As shown in fig. 3, in the terahertz chiral device arranged periodically, the period is 4 × 4 periodic units. The simulation was performed by using CST (Commercial simulation software). Under the condition of terahertz wave incidence, establishing one period of the structure, setting the directions x and y as period boundary conditions, setting the upward direction of the set metal pattern as the direction z, setting the direction as an open boundary condition, simultaneously using the direction as an incident port and an exit port of the terahertz wave, and further obtaining a terahertz wave reflection curve R through simulation-+，R++，，R--，R+-. Subscripts "+" and "-" denote right-hand circular polarization and left-hand circular polarization, respectively, RijIndicating j polarization of incident wave and i polarization of reflected waveAnd (4) the case of chemical conversion. And finally, obtaining an absorption curve of the right-hand circularly polarized wave and an absorption curve of the left-hand circularly polarized wave through calculation. When the circularly polarized wave is incident to the terahertz wave chiral identification device, the absorption rate of the terahertz wave chiral identification device to the right-handed circularly polarized wave is ARThe expression of (a) is as follows:
AR＝1-|R-+|2-|R++|2-|T-+|2-|T++|2；
when the circularly polarized wave is incident to the surface of the terahertz chiral discrimination device, the absorption rate A of the terahertz chiral discrimination device to the left-handed circularly polarized waveLThe expression of (a) is as follows:
AL＝1-|R--|2-|R+-|2-|T--|2-|T+-|2。
wherein A isRThe absorption rate of the terahertz chiral discrimination device to right-handed circularly polarized waves is represented; a. theLRepresenting the absorption rate of the terahertz chiral discrimination device to the left-handed circularly polarized wave; r++Representing the reflection coefficient of a right-hand circularly polarized wave; r--Representing the reflection coefficient of a left-handed circularly polarized wave; t is++Represents the transmission coefficient of the right-hand circularly polarized wave; t is--The transmission coefficient of the left-handed circularly polarized wave is shown; r-+A reflection coefficient representing cross polarization of an incident wave which is a right-handed circularly polarized wave; r+-A reflection coefficient indicating cross polarization of an incident wave which is a left-handed circularly polarized wave; t is-+A transmission coefficient representing cross polarization of an incident wave which is a right-handed circularly polarized wave; t is+-The transmission coefficient of the cross polarization of the incident wave which is a left-handed circularly polarized wave is shown.
If the terahertz chiral discrimination device is a reflection-type device, the transmission coefficient of the left-handed circularly polarized wave and the right-handed circularly polarized wave can be ignored, and the absorptivity A of the terahertz chiral discrimination device to the right-handed circularly polarized wave at the momentRThe following were used:
AR＝1-|R-+|2-|R++|2；
then the absorptivity A of the terahertz chiral discrimination device to the left-handed circularly polarized waveLThe following were used:
AL＝1-|R--|2-|R+-|2；
wherein A isRThe absorption rate of the terahertz chiral discrimination device to right-handed circularly polarized waves is represented; a. theLRepresenting the absorption rate of the terahertz chiral discrimination device to the left-handed circularly polarized wave; r++Representing the reflection coefficient of a right-hand circularly polarized wave; r--Representing the reflection coefficient of a left-handed circularly polarized wave; r-+A reflection coefficient representing cross polarization of an incident wave which is a right-handed circularly polarized wave; r+-The reflection coefficient of the cross polarization of the incident wave which is a left-handed circularly polarized wave is shown.
And the circular dichroism spectrum value obtains a circular dichroism spectrum value (CD) corresponding to the terahertz chiral discrimination device by calculating the difference value between the square of the absorption rate of the left-handed circularly polarized wave and the square of the absorption rate of the right-handed circularly polarized wave. The formula for the circular dichroism value is as follows:
Figure BDA0002669936870000081
wherein CD represents the circular dichroism value, ARThe absorption rate of the terahertz chiral discrimination device to right-handed circularly polarized waves is represented; a. theLThe absorption rate of the terahertz chiral discrimination device to the left-handed circularly polarized wave is shown.
As shown in fig. 4, the absorption curve of the right-hand circularly polarized wave and the absorption curve of the left-hand circularly polarized wave can be expressed. Wherein the abscissa represents frequency, the frequency range is 0.9THz to 1.1THz, and the ordinate represents absorbed energy. When right-handed circularly polarized waves are incident to the terahertz chiral discrimination device, the peak absorption rate at a frequency of 1.019THz is 0.95. When the incident wave is a left-handed circularly polarized wave, the absorptivity in the range of 0.9THz to 1.1THz is lower than 0.11. Therefore, the device exhibits completely different absorption effects for a left-hand circularly polarized wave and a right-hand circularly polarized wave at a frequency of 1.09 THz. Since the difference between the absorptance of the left-hand circularly polarized wave and the absorptance of the right-hand circularly polarized wave is a circular dichroism value, it can be expressed as a strong circular dichroism value.
As shown in fig. 5, in which (a) and (b) are diagrams showing electric field distributions in the xoy plane at the time of incidence of right-hand and left-hand circularly polarized waves, respectively, and in which (c) and (d) are diagrams showing electric field distributions in the xoz plane at the time of incidence of right-hand and left-hand circularly polarized waves, respectively. It can be seen from the diagrams (a) and (b) that when the incident wave is right-hand circular polarized, there is strong electric resonance between the long and short arms of the F-shaped structure, so that most of the energy is absorbed into the medium. When the incident wave is left-handed circular polarized, there is a weak electrical resonance only near the short arm of the F-shaped structure, so only very little electromagnetic wave energy is absorbed. The graphs (c) and (d) show the electric field distribution observed from the xoz plane, and thus it is proved that the right-hand circularly polarized wave is mostly localized in the medium, and absorbed by the formation of surface plasmon.
Referring to fig. 1, in some embodiments, the first direction is a direction that enables the strip metal body, the first strip metal arm, and the second strip metal arm to form an F-shape, or the first direction is a direction that enables the strip metal body, the first strip metal arm, and the second strip metal arm to form a mirror image of the F-shape.
Both sides of the strip-shaped metal body can be represented as a first direction, and if one side is represented as the first direction and an F-shape is formed, the other side can be a mirror image of the F-shape. And the material used and the dimensions are the same as the F-shape formed in the first direction.
Illustratively, the material of the metal layer is gold, and the thickness thereof is 0.2 μm; the dielectric layer is made of polyimide, the dielectric constant of the polyimide is 3.4, the loss tangent of the polyimide is 0.008, the thickness of the polyimide is 33 mu m, the length of the dielectric layer can be 160 mu m, and the width of the dielectric layer can be 160 mu m. The metal pattern layer is made of gold, the metal pattern layer is in an F shape, the thickness of the metal pattern layer is 0.2 mu m, the width of the strip-shaped metal body of the metal pattern is 23 mu m, the length of the strip-shaped metal body is 106 mu m, the length of the long edge of the first strip-shaped metal arm is 61 mu m, and the length of the long edge of the second strip-shaped metal arm is 54 mu m. The first strip-shaped metal arm and the second strip-shaped metal arm have a certain interval therebetween, and the interval can be 12 μm. And taking a device with a mirror image pattern which is set to be F-shaped with the metal pattern as a second terahertz chiral discrimination device.
Fig. 6 is a schematic structural diagram of a second terahertz chiral discrimination device with a plurality of periodic units according to an embodiment of the present invention, and as shown in fig. 6, the number of the periodic units of the second terahertz chiral discrimination device with a plurality of periodic units is 4 × 4.
As shown in fig. 7, after the terahertz wave is incident on the device, it may represent a curve shape similar to that shown in fig. 3, but the difference therebetween is at the frequency of 1.019THz, and fig. 7 represents an absorption curve of a left-hand circularly polarized wave and an absorption curve of a right-hand circularly polarized wave. Wherein the abscissa represents frequency, the frequency range is 0.9THz to 1.1THz, and the ordinate represents absorbed energy. When a left-handed circularly polarized wave is incident to the terahertz chiral discrimination device, the peak absorption rate at a frequency of 1.019THz is 0.95. When the incident wave is right-handed circularly polarized wave, the absorptivity in the range of 0.9 THz-1.1 THz is lower than 0.11.
As shown in fig. 8, at a frequency of 1.019THz, the first terahertz chiral discrimination device strongly absorbs right-handed circularly polarized waves and has little absorption to left-handed circularly polarized waves in a corresponding frequency range. The second terahertz chiral discrimination device strongly absorbs left-handed circularly polarized waves and has small absorption on right-handed circularly polarized waves. The first terahertz chiral discrimination device and the second terahertz chiral discrimination device can discriminate terahertz waves with different chiralities, and the metal patterns on the devices are arranged in a mirror image mode to achieve the discrimination purpose.
The first terahertz chiral discrimination device and the second terahertz chiral discrimination device have opposite absorption effects on circularly polarized waves in two polarization modes. Therefore, the circular dichroism value of the first terahertz chiral discrimination device is the same as that of the second terahertz chiral discrimination device in size, but the signs are opposite. The peak amplitude corresponding to the circular dichroism curve of the device with the two structures at the frequency of 1.018THz is 0.836, so that the difference of the absorption effects of the terahertz chiral discrimination device on the left-handed and right-handed circularly polarized waves at the frequency point can be shown to be large, and the terahertz chiral discrimination device has a strong circular dichroism value. The chiral molecules have different circular dichroism characteristics due to different absorption of the chiral molecules on left-hand circular polarized waves and right-hand circular polarized waves, and the circular dichroism sizes of two enantiomers of the same chiral molecules are the same and are opposite in positive and negative. Therefore, the identification of different chiral molecules and the distinction of chiral molecular enantiomers have important scientific and practical values in the aspects of researching life origin, medicine detection, disease diagnosis and treatment.
In some embodiments, the terahertz chiral discrimination device further includes: a third strip-shaped metal arm; the third strip-shaped metal arm is a structure extending from the second end of the strip-shaped metal body in a second direction perpendicular to the strip-shaped metal body; the first direction is opposite to the second direction.
Wherein the length and width of the third strip-shaped metal arm are respectively 10-900 μm and 10-500 μm. For example, the third strip-shaped metal arm length may be 15 μm, 20 μm, 100 μm, or the like; the third strip-shaped metal arm may have a width of 60 μm, 70 μm, 75 μm, or the like. The third strip-shaped metal arm is positioned on the side opposite to the first strip-shaped metal arm and the second strip-shaped metal arm. And the length of the third strip-shaped metal arm is smaller than that of the first strip-shaped metal arm and larger than that of the second strip-shaped metal arm. The thickness range of the metal pattern layer in the structure can be 0.05-5 mu m; the thickness range of the dielectric layer can be 3-1000 μm; the thickness range of the metal layer can be 0.05-5 μm; the thickness of the metal pattern layer is smaller than that of the metal layer and smaller than that of the dielectric layer. The structure can increase the working frequency range of the terahertz chiral discrimination device, thereby further improving the discrimination accuracy.
Fig. 9 is a schematic structural diagram of a third terahertz chiral discrimination device according to an embodiment of the present invention, and referring to fig. 9, a metal layer is made of gold, and the thickness of the metal layer is 0.2 μm; the dielectric layer is made of polyimide, has a dielectric constant of 3.4, a loss tangent of 0.008 and a thickness of 130 μm, and can have a length of 480 μm and a width of 480 μm. The metal pattern layer is made of gold, the thickness of the metal pattern layer is 0.2 mu m, the length of the strip-shaped metal main body of the metal pattern is set to be 328 mu m, the length of the long edge of the first strip-shaped metal arm is set to be 123 mu m, and the length of the long edge of the second strip-shaped metal arm is set to be 91 mu m; the third strip-shaped metal arm had a length of 105 μm and a width of 80 μm. The first strip-shaped metal arm and the second strip-shaped metal arm are spaced at a certain interval, and the interval can be 40 μm. As shown in fig. 10, it is a third terahertz chiral discrimination device of a plurality of periodic units.
The length and width of the dielectric layer are shown as that only one set metal pattern is included in the metal pattern layer on the dielectric layer, and if the metal pattern units are a plurality of metal pattern units which are arranged periodically, all metals can be set according to the parameters of each metal pattern layer, the parameters of the dielectric layer and the parameters of the metal layer. As can be seen from fig. 11, when a right-hand circularly polarized wave is incident on the device, the device has absorption peaks at frequencies of 0.31THz and 0.38THz for the right-hand circularly polarized wave, and the absorptances thereof are 0.826 and 0.745, respectively. When a left-handed circularly polarized wave is incident to the terahertz wave chirality discriminating device, absorptances at frequencies of 0.31THz and 0.38THz are 0.14 and 0.19, respectively. Compared with the first terahertz chiral discrimination device, the terahertz chiral discrimination device can simultaneously have strong absorption on right-handed circularly polarized waves and little absorption on left-handed circularly polarized waves in two wave bands, and the terahertz chiral discrimination device with the structure increases the working frequency range in use.
Fig. 12 is a schematic diagram of the electric field distribution of a third terahertz chiral discrimination device at the first maximum circular dichroism position according to an embodiment of the present invention. Fig. 13 is a schematic diagram of the electric field distribution of a third terahertz chiral discrimination device at the second maximum circular dichroism position according to an embodiment of the present invention. As shown in fig. 12 and 13, (a) and (b) in fig. 12 show the electric field distribution of the xoy plane at the first maximum circular two-color spectrum position 0.31THz when right-hand and left-hand circularly polarized waves are incident, respectively, and (c) and (d) in fig. 12 show the electric field distribution of the xoz plane at the first maximum circular two-color spectrum position 0.31THz when right-hand and left-hand circularly polarized waves are incident, respectively. Whereas the graphs (a) and (b) in fig. 13 show the electric field distribution of the xoy plane at the second maximum circular dichroism position 0.38THz when right-hand and left-hand circularly polarized waves are incident, respectively, the graphs (c) and (d) in fig. 13 show the electric field distribution of the xoz plane at the second maximum circular dichroism position 0.38THz when right-hand and left-hand circularly polarized waves are incident, respectively. Therefore, it can be seen that, at the two maximum circular dichroism positions, when the incident wave is right-hand circular polarized, the right-hand circular polarized wave is mostly localized in the medium, forming surface plasmons to be absorbed. When the incident wave is left-handed circular polarization, the resonance generated in the third device is weak, and only a small amount of energy is absorbed, so that a strong circular dichroism value is obtained.
Fig. 14 is a schematic structural diagram of a fourth terahertz chiral discrimination device according to an embodiment of the present invention. As shown in fig. 14, in some embodiments, the first direction is a direction in which the strip metal body, the first strip metal arm, and the second strip metal arm form an F-shape, or the first direction is a direction in which the strip metal body, the first strip metal arm, and the second strip metal arm form a mirror image of an F-shape.
Both sides of the strip-shaped metal body can be represented as a first direction, and if one side is represented as the first direction and an F-shape is formed, the other side can be a mirror image of the F-shape. And the third strip-shaped metal arm in the second direction changes along with the change of the first direction. And the material and the size are the same as those of the set metal pattern formed in the first direction.
Illustratively, the material of the metal layer is gold, and the thickness thereof is 0.2 μm; the dielectric layer is made of polyimide, has a dielectric constant of 3.4, a loss tangent of 0.008 and a thickness of 130 μm, and can have a length of 480 μm and a width of 480 μm. The metal pattern layer is made of gold, the thickness of the metal pattern layer is 0.2 mu m, the length of a strip-shaped metal body of the metal pattern is set to be 328 mu m, the length of a long edge of the first strip-shaped metal arm is set to be 123 mu m, and the length of a long edge of the second strip-shaped metal arm is set to be 91 mu m; the third strip-shaped metal arm had a length of 105 μm and a width of 80 μm. The first strip-shaped metal arm and the second strip-shaped metal arm are spaced at a certain interval, and the interval can be 40 μm. As shown in fig. 15, a fourth terahertz chiral discrimination device is a plurality of periodic units.
Specifically, as shown in fig. 16, when a left-hand circularly polarized wave is incident on the device, the device has absorption peaks at 0.31THz and 0.38THz for the left-hand circularly polarized wave, and the absorptances are 0.826 and 0.745, respectively. When right-hand circularly polarized waves are incident on the device, the absorptances at 0.31THz and 0.38THz are 0.14 and 0.19, respectively. Compared with a second terahertz chiral discrimination device, the terahertz chiral discrimination device with the structure can simultaneously absorb left-handed circularly polarized waves in two wave bands, but hardly absorb right-handed circularly polarized waves, so that the working frequency range of the device is enlarged.
Taking the terahertz chiral discrimination device with the third metal arm as a third terahertz chiral discrimination device; and a mirror image pattern of a set metal pattern with a third metal arm is used as a fourth terahertz chiral discrimination device. As shown in fig. 17, at the frequencies of 0.31THz and 0.38THz, the third terahertz chiral discrimination device strongly absorbs right-handed circularly polarized waves and has little absorption to left-handed circularly polarized waves in the corresponding frequency range. The fourth terahertz chiral discrimination device strongly absorbs left-handed circularly polarized waves and has small absorption on right-handed circularly polarized waves. The third terahertz chiral discrimination device and the fourth terahertz chiral discrimination device can discriminate incident terahertz waves with different chiralities, the metal patterns on the devices are arranged in a mirror image mode to achieve the discrimination purpose, and meanwhile, a third metal arm is added to increase the working frequency range of the devices.
In addition, the device can also be applied to an antenna, the terahertz wave chiral discrimination device is positioned at the front end of the antenna, and under the condition that the antenna receives terahertz waves, left-hand circularly polarized waves and right-hand circularly polarized waves are distinguished to obtain corresponding terahertz waves. If the antenna needs to receive right-handed circularly polarized waves, the terahertz wave chiral discrimination device can reflect the unwanted waves. For example, when the left-hand circularly polarized wave and the right-hand circularly polarized wave reach the surface of the terahertz wave chiral discrimination device at the same time, the terahertz wave chiral discrimination device corresponding to the right-hand circularly polarized wave absorbs the corresponding wave, reflects most of the left-hand circularly polarized wave, and only a very small part of the left-hand circularly polarized wave is absorbed.
According to another aspect of the embodiments of the present invention, there is provided a circular polarized wave selector, including: a terahertz chiral discrimination device as described in the above embodiments.
The conventional circularly polarized wave selector is an optical path identification system consisting of a quarter-wave plate and a linear polarizer, so that the conventional circularly polarized wave selector is high in complexity and is not beneficial to use.
In order that those skilled in the art will better understand the present invention, embodiments of the present invention will be described below with reference to specific examples.
As further shown in fig. 2, a terahertz chiral discrimination device of an embodiment includes: f-shaped metal structure layer, dielectric layer and metal plate.
The periodic unit is composed of an F-shaped metal structure layer, a dielectric layer and a metal plate from top to bottom in sequence, and the periods in the x direction and the y direction are Px and Py respectively.
The period length in the x direction is Px, and the length is 50-1000 μm.
The period length in the y direction is Py, and the length is 50-1000 μm.
Referring to fig. 2, the width w of the F-shaped metal structure layer ranges from 10 μm to 500 μm, the length L ranges from 5 μm to 900 μm, the length s1 of the long arm ranges from 10 μm to 900 μm, and the length s2 of the short arm ranges from 10 μm to 900 μm.
The thickness range of the F-shaped metal structure layer is 0.05-5 mu m.
The material of the F-shaped metal structure layer can be gold, aluminum or copper.
The dielectric constant of the middle dielectric layer is 1-20, the loss tangent angle range is 0-0.2, and the thickness range is 3-1000 mu m.
The intermediate dielectric layer is polyimide, silicon dioxide, silicon and the like.
The thickness of the metal floor layer is not less than 0.05 μm. The metal material may be gold, aluminum, or copper.
In this example, the dielectric material was polyimide with a dielectric constant of 3.4 and a loss tangent of 0.008, and the metal material was gold with a conductivity of 4.56X 107And (5) S/m. Dielectric layerThe thickness of the square plate-shaped structure positioned in the middle of the periodic unit is d. The metal structure of the upper surface of the media is in the shape of the letter F with a thickness t1 and the relevant dimensional parameters are shown in fig. 3. The metal layer on the lower surface of the medium is a metal plate with the same period as the unit, and the thickness is t 2. Exemplary values of Px ═ Py 160 μm, d ═ 33 μm, t1 ═ 0.2 μm, t2 ═ 1 μm, w ═ 23 μm, L ═ 106 μm, m ═ 12 μm, s1 ═ 61 μm, and s2 ═ 54 μm.
As shown in fig. 3, the number of the periodic units of the first terahertz chiral discrimination device of the plurality of periodic units is 4 × 4. In an actual process, the number of the periodic units included in the device is not limited thereto. If the actual period number of the terahertz chiral super surface is mxn, generally, m is larger than or equal to 10, and n is larger than or equal to 10.
As shown in fig. 1, a second terahertz chiral super surface can be obtained by mirroring the F metal pattern structure of the terahertz chiral super surface of the first structure. The second terahertz chiral super-surface shown in fig. 1 is a side view of a terahertz chiral super-surface of 1 periodic unit.
It can be seen that the periodic cells in fig. 1 differ from the periodic cells in fig. 2 in the orientation of the F-shaped structures, which are mirror images of each other. The structural size of the second terahertz chiral super surface is consistent with the parameters of the first terahertz chiral super surface.
As shown in fig. 6, the number of the periodic units of the second terahertz chiral discrimination device of the plurality of periodic units is 4 × 4. In actual processing, the number of the periodic units included in the device is not limited thereto. The actual period number of the terahertz chiral super surface is mxn, generally, m is more than or equal to 10, and n is more than or equal to 10.
As shown in fig. 4, wherein the solid line and the broken line correspond to aRAnd ALThe absorption of the structure to right-hand circularly polarized waves and left-hand circularly polarized waves respectively. The result is obtained by adopting three-dimensional electromagnetic field simulation software CST simulation. During calculation, firstly, one period of the structure is established, then, the x and y directions are set as period boundary conditions, the z direction is set as an open boundary condition and is used as an incident port and an emergent port, and a reflection curve R can be obtained through simulation-+，R++，R--，R+-. Subscripts "+" and "-" denote right-hand circular polarization and left-hand circular polarization, respectively, RijThis shows the case where the incident wave is j-polarized and the reflected wave is i-polarized. When the circularly polarized wave is incident to the terahertz chiral discrimination device, the absorption rate of the terahertz chiral discrimination device to the right-handed circularly polarized wave is ARThe expression of (a) is as follows:
AR＝1-|R-+|2-|R++|2-|T-+|2-|T++|2； (1)
when the circularly polarized wave is incident to the surface of the terahertz chiral discrimination device, the absorption rate of the terahertz chiral discrimination device to the left-handed circularly polarized wave is ALThe expression of (a) is as follows:
AL＝1-|R--|2-|R+-|2-|T--|2-|T+-|2； (2)
wherein A isRThe absorption rate of the terahertz chiral discrimination device to right-handed circularly polarized waves is represented; a. theLRepresenting the absorption rate of the terahertz chiral discrimination device to the left-handed circularly polarized wave; r++Representing the reflection coefficient of a right-hand circularly polarized wave; r--Representing the reflection coefficient of a left-handed circularly polarized wave; t is++Represents the transmission coefficient of the right-hand circularly polarized wave; t is--The transmission coefficient of the left-handed circularly polarized wave is shown; r-+A reflection coefficient representing cross polarization of an incident wave which is a right-handed circularly polarized wave; r+-A reflection coefficient indicating cross polarization of an incident wave which is a left-handed circularly polarized wave; t is-+A transmission coefficient representing cross polarization of an incident wave which is a right-handed circularly polarized wave; t is+-The transmission coefficient of the cross polarization of the incident wave which is a left-handed circularly polarized wave is shown.
If the terahertz chiral discrimination device is a reflection-type device, the absorption rate A of the terahertz chiral discrimination device to the right-hand circularly polarized wave can be obtained without considering the transmission items of the left-hand circularly polarized wave and the right-hand circularly polarized waveRThe following were used:
AR＝1-|R-+|2-|R++|2； (3)
then the absorptivity A of the terahertz chiral discrimination device to the left-handed circularly polarized waveLThe following were used:
AL＝1-|R--|2-|R+-|2； (4)
wherein A isRThe absorption rate of the terahertz chiral discrimination device to right-handed circularly polarized waves is represented; a. theLRepresenting the absorption rate of the terahertz chiral discrimination device to the left-handed circularly polarized wave; r++Representing the reflection coefficient of a right-hand circularly polarized wave; r--Representing the reflection coefficient of a left-handed circularly polarized wave; r-+A reflection coefficient representing cross polarization of an incident wave which is a right-handed circularly polarized wave; r+-The reflection coefficient of the cross polarization of the incident wave which is a left-handed circularly polarized wave is shown.
And the circular dichroism spectrum value obtains a circular dichroism spectrum value (CD) corresponding to the terahertz chiral discrimination device by calculating the difference value between the square of the absorption rate of the left-handed circularly polarized wave and the square of the absorption rate of the right-handed circularly polarized wave. The formula for the circular dichroism value is as follows:
Figure BDA0002669936870000151
wherein CD represents the circular dichroism value, ARThe absorption rate of the terahertz chiral discrimination device to right-handed circularly polarized waves is represented; a. theLThe absorption rate of the terahertz chiral discrimination device to the left-handed circularly polarized wave is shown. Finally, an absorption curve A of the first terahertz chiral super-surface to the right-handed circularly polarized wave is calculated by a formula (3) and a formula (4) respectivelyRAnd absorption curve A of left-handed circularly polarized wavesLAnd then the circular dichroism spectrum (CD) of the device is obtained from the formula (5), as shown in fig. 6.
The solid line in fig. 4 represents the absorption curve of the first chiral device for right-hand circularly polarized waves, and the dashed line represents the absorption curve of the first device for left-hand circularly polarized waves. The abscissa represents frequency, the frequency range is 0.9THz to 1.1THz, and the ordinate represents absorption. When right-hand circularly polarized waves are incident on the first chiral super surface, the peak absorptance at 1.019THz reaches 0.95. When the incident wave is a left-handed circularly polarized wave, the absorptivity in the range of 0.9THz to 1.1THz is lower than 0.11. Therefore, the first chiral super-surface has completely different absorption effects on two types of circularly polarized waves near 1.09THz, the difference value is the circular dichroism value, and therefore the structure has a strong circular dichroism value.
Fig. 7 is a schematic diagram of absorption spectra of left-hand and right-hand circularly polarized waves of a second terahertz chiral discrimination device according to an embodiment of the present invention. As shown in fig. 7, although the curve shapes of fig. 7 and fig. 4 are completely consistent, the essential difference is that at 1.019THz, the absorption effects of the first device and the second device on the right-and-left circularly polarized waves in the corresponding frequency ranges are opposite. The second device has strong absorption to left-hand circularly polarized waves and small absorption to right-hand circularly polarized waves. The first device strongly absorbs right-handed circularly polarized waves and has little absorption to left-handed circularly polarized waves.
Fig. 8 is a schematic diagram of circular dichroism values corresponding to first and second terahertz chiral discrimination devices according to an embodiment of the present invention. As shown in FIG. 8, the absorption effects of the first chiral super-surface and the second chiral super-surface on the circularly polarized waves of the two polarization modes are opposite. Therefore, the circular dichroism value of the first terahertz chiral super surface is the same as that of the second terahertz chiral super surface, but the signs are opposite. The peak amplitude of the circular dichroism curve of the two structures at 1.018THz is 0.836, which shows that the difference of the absorption effect of the chiral super surface on the left-hand and right-hand circularly polarized waves at the frequency point is large, so that the circular dichroism value is strong.
As shown in fig. 5, in which the graphs (a) and (b) are the electric field distributions of the xoy plane at the time of incidence of the right-hand and left-hand circularly polarized waves, respectively, and in which the graphs (c) and (d) are the electric field distributions of the xoz plane at the time of incidence of the right-hand and left-hand circularly polarized waves, respectively. As can be seen from the diagrams (a) and (b), when the incident wave is right-hand circularly polarized, there is strong electrical resonance between the long and short arms of the F-shaped structure, so that most of the energy is absorbed into the medium. When the incident wave is left-handed circular polarized, there is a weak electrical resonance only near the short arm of the F-shaped structure, so only very little electromagnetic wave energy is absorbed. The graphs (c) and (d) show the electric field distribution from the other observation plane (xoz plane), and thus it is proved that the right-hand circularly polarized wave is mostly localized in the medium, forms surface plasmon and is absorbed.
Referring to fig. 9, fig. 9 shows a side view of a third type of terahertz chiral super surface 1 periodic unit. In fig. 9, the periodic unit is similar to that of the first type of terahertz chiral super surface, and the same material is used, except that a piece of metal is added at the tail end of the F-type metal structure. The corresponding dimensional parameters are shown in fig. 9. Illustratively, the parameters are as follows: Px-Py-480 μm, d-130 μm, t 1-0.2 μm, t 2-0.2 μm, w-80 μm, L-328 μm, m-40 μm, s 1-123 μm, s 2-91 μm, and s 3-105 μm.
As shown in fig. 10, a side view of a third terahertz chiral super-surface of a 4 × 4 periodic unit is shown. In actual processing, the number of the periodic units included in the device is not limited thereto. The actual period number of the terahertz chiral super surface is mxn, generally, m is more than or equal to 10, and n is more than or equal to 10.
Fig. 11 is a schematic diagram of absorption spectra of left-hand and right-hand circularly polarized waves of a third terahertz chiral discrimination device according to an embodiment of the present invention. As shown in fig. 11, when a right-hand circularly polarized wave is incident on the third terahertz chiral super-surface, the device has absorption peaks at 0.31THz and 0.38THz for the right-hand circularly polarized wave, and the absorptances are 0.826 and 0.745 respectively. When a left-handed circularly polarized wave is incident to the third terahertz chiral super surface, absorptances at 0.31THz and 0.38THz are 0.14 and 0.19, respectively. Compared with the first type of terahertz chiral super-surface, the third type of terahertz chiral super-surface has the characteristics that the right-handed circularly polarized waves can be strongly absorbed at two wave bands, the left-handed circularly polarized waves can be hardly absorbed, and the working frequency range of the device is enlarged.
As shown in fig. 14, fig. 14 shows a side view of a fourth type of terahertz chiral super-surface of 1 periodic unit. The periodic unit is similar to that of the second type terahertz chiral super-surface, the used materials are the same, and only one piece of metal is added at the tail end of the F-shaped metal structure. The corresponding dimensions are exemplary as follows: Px-Py-480 μm, d-130 μm, t 1-0.2 μm, t 2-0.2 μm, w-80 μm, L-328 μm, m-40 μm, s 1-123 μm, s 2-91 μm, and s 3-105 μm.
Fig. 15 is a schematic structural diagram of a fourth terahertz chiral discrimination device with multiple periodic units according to an embodiment of the present invention. As shown in fig. 15, fig. 15 shows a side view of a fourth terahertz chiral super-surface that is a 4 × 4 periodic unit. In actual processing, the number of the periodic units included in the device is not limited thereto. The actual period number of the terahertz chiral super surface is mxn, generally, m is more than or equal to 10, and n is more than or equal to 10.
Fig. 16 is a schematic diagram of absorption spectra of left and right circularly polarized waves of a fourth terahertz chiral discrimination device according to an embodiment of the present invention. As can be seen from fig. 16, when a right-hand circularly polarized wave is incident on the fourth terahertz chiral super-surface, the device has absorption peaks at 0.31THz and 0.38THz for a left-hand circularly polarized wave, and the absorption rates are 0.826 and 0.745 respectively. When right-hand circularly polarized waves are incident on the fourth terahertz chiral super-surface, the absorptances at 0.31THz and 0.38THz are 0.14 and 0.19, respectively. Compared with the second type of terahertz chiral super-surface, the fourth type of terahertz chiral super-surface has the characteristics that the right-handed circularly polarized waves can be absorbed strongly at two wave bands, the left-handed circularly polarized waves can be absorbed less, and the working frequency range of the device is enlarged.
Fig. 17 is a schematic diagram of a circular dichroism curve of a fourth terahertz chiral discrimination device according to an embodiment of the present invention. As shown in fig. 17, the solid line and the dotted line of fig. 17 are circular dichroism curves of the third and fourth terahertz chiral super-surfaces provided by the embodiment of the present invention, respectively. The absorption effects of the third chiral super surface and the fourth chiral super surface on the circularly polarized waves of the two polarization modes are just opposite. Therefore, the circular dichroism value of the third terahertz chiral super surface is the same as that of the fourth terahertz chiral super surface, but the sign is opposite. The circular dichroism curves of the two structures have peak amplitudes of 0.663 and 0.51 at 0.31THz and 0.381THz respectively.
In summary, the terahertz chiral discrimination device and the circular polarization selector of the embodiments of the invention pass through the metal layer; the dielectric layer is positioned on one side of the metal layer; the metal pattern layer is positioned on one side of the dielectric layer, which is far away from the metal layer, and comprises metal pattern units which are periodically arranged; the metal pattern unit comprises a set metal pattern, the set metal pattern comprises a strip-shaped metal main body, a first strip-shaped metal arm and a second strip-shaped metal arm, the first strip-shaped metal arm is a structure extending from the first end of the strip-shaped metal main body along a first direction perpendicular to the strip-shaped metal main body, and one end of the second strip-shaped metal arm is vertically connected with the middle part of the strip-shaped metal main body; the length of the first strip-shaped metal arm is greater than that of the second strip-shaped metal arm; the first strip-shaped metal arm and the second strip-shaped metal arm are located on the same side of the strip-shaped metal main body. The circular dichroism spectrum value of the terahertz wave chiral discrimination device, the antenna and the circularly polarized wave selector is greater than 0.836 in the terahertz frequency band. And a strip structure is introduced at the tail end of the F, so that the dual-band circular dichroism characteristic can be realized, and the circular dichroism values corresponding to the dual bands are all larger than 0.745. The device can be used for detecting the terahertz chiral molecules and has important application value in the aspect of terahertz circular polarization selectors.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments in the present invention.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made to the embodiment of the present invention by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (8)

1. A terahertz chiral discrimination device, comprising:
a metal layer;
the dielectric layer is positioned on one side of the metal layer;
the metal pattern layer is positioned on one side of the dielectric layer, which is far away from the metal layer, and comprises metal pattern units which are periodically arranged; the metal pattern unit comprises a set metal pattern, the set metal pattern is composed of a strip metal main body, a first strip metal arm and a second strip metal arm or composed of the strip metal main body, the first strip metal arm, the second strip metal arm and a third strip metal arm, the first strip metal arm is a structure extending from the first end of the strip metal main body along a first direction perpendicular to the strip metal main body, and one end of the second strip metal arm is perpendicularly connected with the strip metal main body; the first strip-shaped metal arm and the second strip-shaped metal arm are positioned on the same side of the strip-shaped metal main body; the length of the first strip-shaped metal arm is greater than that of the second strip-shaped metal arm; the third strip-shaped metal arm is a structure extending from the second end of the strip-shaped metal body in a second direction perpendicular to the strip-shaped metal body; the first direction is opposite to the second direction.
2. The terahertz chiral discrimination device of claim 1, wherein the third strip metal arm is shorter in length than the first strip metal arm and longer than the second strip metal arm.
3. The terahertz chiral discrimination device of claim 1, wherein the first direction is a direction in which the strip metal body, the first strip metal arm, and the second strip metal arm form an F-shape, or a direction in which the strip metal body, the first strip metal arm, and the second strip metal arm form an F-shape mirror image.
4. The terahertz chiral discrimination device of claim 1, wherein the metal layer and the metal pattern layer are made of a material comprising gold, aluminum, or copper; the material used for the dielectric layer comprises polyimide, silicon dioxide or silicon.
5. The terahertz chiral discrimination device of claim 3, wherein the length ranges of the length and the width of the strip-shaped metal main body are 5-900 μm and 10-500 μm, respectively; the length range of the long edge of the first bar-shaped metal arm is 10-900 mu m; the length range of the long edge of the second strip-shaped metal arm is 10-900 mu m; the length ranges of the length and the width of the third strip-shaped metal arm are respectively 10 mu m-900 mu m and 10 mu m-500 mu m.
6. The terahertz chiral discrimination device of claim 5, wherein the thickness of the metal pattern layer ranges from 0.05 μm to 5 μm; the thickness range of the medium layer is 3-1000 mu m; the thickness of the metal layer is not less than 0.05 [ mu ] m; the thickness of the metal pattern layer is smaller than that of the dielectric layer, and the thickness of the metal pattern layer is smaller than that of the metal layer.
7. The terahertz chiral discrimination device of claim 3, wherein the length of the sides of each metal pattern unit ranges from 50 μm to 1000 μm; the distance between each set metal pattern and each edge of the corresponding metal pattern unit is the same.
8. A circular polarization selector, comprising: the terahertz chiral discrimination device of any one of claims 1 to 7.
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