CN113866229B - high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface and implementation method thereof - Google Patents
high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface and implementation method thereof Download PDFInfo
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Abstract
The invention discloses a high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface and an implementation method thereof. The invention adopts a plurality of eccentric artificial local surface plasmon basic units to be arranged into a periodic two-dimensional array, so that the geometric center and the gravity center of the circular grating have offset, namely the circular grating is an eccentric structure; the eccentric structure breaks the symmetry of a concentric structure, so that a high-order mode is degenerated into a quasi-BIC mode with a very high Q value, and the high-order mode is excited; the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing; the invention has the advantages of multiple resonance points, wide frequency band and field enhancement, and is used for millimeter wave sensing, material detection, tactical stealth, biomedicine and the like.
Description
Technical Field
The invention relates to a millimeter wave sensing technology, in particular to a high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface and an implementation method thereof.
Background
Artificial Localized Surface Plasmons (LSSPs) have received much attention from researchers due to their properties of sub-wavelength manipulation and near-field enhancement. Because the texture structure can reduce the plasma frequency of metal, the microwave frequency band can imitate the natural Local Surface Plasmons (LSPs) of an optical frequency band, and can be made into novel passive microwave devices such as a sensor, a band-pass filter, an Orbital Angular Momentum (OAM) antenna, an electromagnetic stealth coating and the like.
Among them, millimeter wave sensing based on artificial local surface plasmons is a promising application. It has been confirmed by Radar Cross Section (RCS) analysis that electromagnetic waves can be excited when they are incident from the sideAnd emitting a plurality of artificial local surface plasmon modes. However, when the electromagnetic wave is incident from the front, only the TE of the lowest order can be excited 1,1 Mode, higher order mode (TE) 2,1 And above) are Bound States in the symmetrically protected Continuum (BIC) that are not excited. However, front incidence is the most common case of millimeter wave sensing, such as echo reception of vehicle-mounted radar and transmitted wave reception of millimeter wave security inspection, and the phase plane of electromagnetic waves is parallel to the receiving plane.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a high-Q-value eccentric artificial local surface plasmon Quasi-BIC super surface, and an eccentric structure enables a high-order mode to be degenerated into a Quasi Bound States in the continuous domain (Quasi-BIC) mode with extremely high Q value, so that the Quasi Bound States can be excited by electromagnetic waves incident from the front. Compared with the super-surface of other structures, the structure has the advantages of multiple resonance points, wide frequency band and field enhancement, and can be used for millimeter wave sensing, substance detection, tactical stealth, biomedicine and the like.
The invention aims to provide a high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface.
The high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface comprises: the device comprises a substrate and an eccentric artificial local surface plasmon basic unit; forming M multiplied by N eccentric artificial local surface plasmon basic units distributed in a periodic two-dimensional array on a substrate, wherein M and N are integers more than or equal to 3; each eccentric artificial local surface plasmon basic unit is a circular grating with a hollow circle therein, so that the geometric center and the gravity center of the circular grating are offset, namely the circular grating is in an eccentric structure; the width of the edge of the circular grating is b, and the outer radius of the teeth (teeth) of the circular grating is R 2 The number of teeth is N, the grating period is d, N is more than 30, so that the grating period d is far less than the wavelength of the incident plane electromagnetic wave, namely the grating period is less than or equal to one tenth of the wavelength of the plane electromagnetic wave, the grating duty ratio is a/d, and the radius of the hollow circle is R 1 (ii) a There are two eccentric modes to realize the eccentric structure: aThe other is that the hollow circle is not concentric, and the grating structure is not uniform; in the eccentric mode that the hollow circle is not concentric, the teeth of the circular grating are uniformly distributed, and the distance between the center of the hollow circle and the center of the circular grating is delta L; in the eccentric mode of uneven grating structure, the center of a hollow circle coincides with the center of a circular grating, but teeth of the circular grating are unevenly distributed, namely one or more parameters of grating constant, duty ratio, spacing and length are unevenly distributed, so that the geometric center and the center of gravity of the circular grating are offset, and the spacing between the geometric center and the center of gravity is delta L; the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, and the period of the periodic two-dimensional array is D +2(b + R) 2 ) (ii) a The normal incidence of a plane electromagnetic wave (TEM) is to the quasi-BIC super surface, namely the wave vector direction of the plane electromagnetic wave is vertical to the quasi-BIC super surface, an equiphase plane is parallel to the quasi-BIC super surface, the electric field and the magnetic field of the plane electromagnetic wave are both parallel to the surface, and the direction of the electric field is parallel to the eccentric displacement direction; in the concentric structure of the circular grating with the geometric center coinciding with the center of gravity, the TE mode of the fundamental mode is used when the planar electromagnetic wave is incident from the front 1,1 Is a resonant Leaky Mode (Leaky Mode) that can be excited, and a higher order Mode (TE) 2,1 And above) is a symmetrically protected BIC mode, which has no normal component in its radiation far field, cannot couple with a planar electromagnetic wave, and cannot be excited; the eccentric structure breaks the symmetry of the concentric structure, so that a radiation far field of a high-order mode generates a normal component, the high-order mode is degenerated into a symmetrical protection type quasi-BIC mode with a high Q value, and the high-order mode is excited; in quasi-BIC super-surface of eccentric structure, basic mode TE 1,1 Can still be excited, and the resonant frequency of the resonant circuit has slight change; the number of the high-order modes is multiple, the resonant frequency corresponding to each mode is spaced, and a frequency reference can be provided for the spectrometer; the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing; the smaller the distance delta L between the center of the hollow circle and the center of the circular grating is, the narrower the peak corresponding to the high-order mode is, and the larger the corresponding Q value is.
The frequency of the planar electromagnetic wave is a microwave frequency band (0.3-300 GHz) or a terahertz frequency band (300-3000 GHz).
The substrate is Printed Circuit Board (PCB) or silicon dioxide (SiO) 2 ) (ii) a For a quasi-BIC super surface applied to a microwave frequency band, a printed circuit board is adopted as a substrate; for a quasi-BIC super surface applied to a terahertz frequency band, a substrate adopts silicon dioxide.
The material of the circular grating is high-conductivity metal, copper or silver.
When the quasi-BIC super surface works in the microwave frequency band, the outer radius R of the teeth of the circular grating 2 Is millimeter magnitude, when the quasi-BIC super surface works in a terahertz frequency band, the outer radius R of the teeth of the circular grating 2 On the order of microns; r is 2 /4≤R 1 ≤R 2 2; the duty ratio a/d of the grating is 0.2-0.8; r is 2 /20≤b≤R 2 /10；R 2 /4≤D≤2R 2 。
Further, the quasi-BIC super surface is positioned in a background material, the background material is vacuum or gas or liquid with dielectric constant not 1, and trace gas is detected through the change of resonance frequency caused by the change of dielectric constant of a medium of the background material.
The invention also aims to provide a realization method of the high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface.
The invention discloses a method for realizing a high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface, which comprises the following steps of:
1) providing a quasi BIC super-surface:
a) forming M multiplied by N eccentric artificial local surface plasmon basic units distributed in a periodic two-dimensional array on a substrate, wherein M and N are integers more than or equal to 3;
b) each eccentric artificial local surface plasmon basic unit is a circular grating with a hollow circle therein, so that the geometric center and the gravity center of the circular grating are offset, namely the circular grating is in an eccentric structure;
c) the width of the edge of the circular grating is b, and the outer radius of the teeth (teeth) of the circular grating is R 2 The number of teeth is N, the grating period is d, N is more than 30The grating period d is far less than the wavelength of the incident plane electromagnetic wave, namely the grating period is less than or equal to one tenth of the wavelength of the electromagnetic wave, the grating duty ratio is a/d, and the radius of the hollow circle is R 1 ；
d) There are two eccentric modes to realize the eccentric structure: one is that the hollow circle is not concentric, and the other is that the grating structure is not uniform; the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, the period of the periodic two-dimensional array is D +2(b + R) 2 )：
i. In the eccentric mode that the hollow circle is not concentric, the teeth of the circular grating are uniformly distributed, and the distance between the center of the hollow circle and the center of the circular grating is delta L;
ii, in an eccentric mode with uneven grating structure, the center of a hollow circle coincides with the center of a circular grating, but teeth of the circular grating are unevenly distributed, namely one or more parameters of grating constant, duty ratio, spacing and length are unevenly distributed, so that the geometric center and the center of gravity of the circular grating are shifted, and the spacing between the geometric center and the center of gravity is delta L;
e) the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, and the period of the periodic two-dimensional array is D +2(b + R) 2 )；
2) The normal incidence of a planar electromagnetic wave (TEM) to a quasi-BIC super surface, namely the wave vector direction of the planar electromagnetic wave is vertical to the quasi-BIC super surface, an isophase plane is parallel to the quasi-BIC super surface, the electric field and the magnetic field of the planar electromagnetic wave are both parallel to the surface, and the direction of the electric field is parallel to the eccentric displacement direction;
3) in the concentric structure of the circular grating with the geometric center coinciding with the center of gravity, the TE mode of the fundamental mode is used when the planar electromagnetic wave is incident from the front 1,1 Is a resonant Leaky Mode (Leaky Mode) that can be excited, and a higher order Mode (TE) 2,1 And above) is a symmetrically protected BIC mode, with no normal component in its far field of radiation, unable to couple with a planar electromagnetic wave, unable to be excited; the eccentric structure breaks the symmetry of a concentric structure, so that a high-order modeThe radiation far field generates a normal component, so that a high-order mode is degenerated into a symmetrical protection type quasi-BIC mode with a high Q value, and the high-order mode is excited;
4) in quasi-BIC super-surfaces of eccentric structure, the basic mode TE 1,1 Can still be excited, and the resonant frequency of the resonant circuit has slight change; the number of the high-order modes is multiple, the resonant frequency corresponding to each mode is spaced, and a frequency reference can be provided for the spectrometer; the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing; the smaller the distance delta L between the center of the hollow circle and the center of the circular grating is, the narrower the peak corresponding to the high-order mode is, and the larger the corresponding Q value is.
Further, the quasi-BIC super-surface is placed in a background material, and the trace gas is detected through the change of the resonant frequency caused by the change of the dielectric constant of the medium of the background material.
The invention has the advantages that:
according to the invention, a plurality of eccentric artificial local surface plasmon basic units are arranged into a periodic two-dimensional array, so that the geometric center and the gravity center of the circular grating have offset, namely the circular grating is of an eccentric structure; the eccentric structure breaks the symmetry of a concentric structure, so that a high-order mode is degenerated into a quasi-BIC mode with a very high Q value, and the high-order mode is excited; the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing; the invention has the advantages of multiple resonance points, wide frequency band and field enhancement, and is used for millimeter wave sensing, material detection, tactical stealth, biomedicine and the like.
Drawings
FIG. 1 is a schematic diagram of one embodiment of a high Q eccentric artificial local surface plasmon quasi-BIC super surface of the present invention;
FIG. 2 is a schematic diagram of an eccentric artificial local surface plasmon base unit according to an embodiment of the high Q-value eccentric artificial local surface plasmon quasi-BIC super surface of the present invention;
FIG. 3 is a graph of transmission coefficients of a super-surface of a concentric structure;
FIG. 4 is a graph of the reflectance of a super-surface of a concentric structure;
FIG. 5 shows the upper excited TE of a super-surface with a concentric structure 1,1 A pattern electric field profile;
FIG. 6 is a graph of transmission coefficients for one embodiment of a high Q eccentric artificial local surface plasmon quasi-BIC super surface of the present invention;
FIG. 7 is a reflection coefficient plot for one embodiment of a high Q eccentric artificial local surface plasmon quasi-BIC super surface of the present invention;
FIG. 8 is TE excited by one embodiment of a high Q eccentric artificial local surface plasmon quasi-BIC super surface of the present invention 2,1 A pattern electric field profile;
FIG. 9 is TE excited by one embodiment of a high Q eccentric artificial local surface plasmon quasi-BIC super surface of the present invention 3,1 A pattern electric field profile;
FIG. 10 is a transmission coefficient plot for one embodiment of a high Q eccentric artificial local surface plasmon quasi-BIC super surface of the present invention;
FIG. 11 is a reflection coefficient plot for one embodiment of a high Q-value eccentric artificial local area surface plasmon quasi-BIC super surface of the present invention.
Detailed Description
The invention will be further elucidated by means of specific embodiments in the following with reference to the drawing.
As shown in fig. 1, the high-Q-value eccentric artificial local surface plasmon quasi BIC super surface of the present embodiment includes: the device comprises a base body and an eccentric artificial local surface plasmon basic unit; forming M multiplied by N eccentric artificial local surface plasmon basic units distributed in a periodic two-dimensional array on a substrate; as shown in fig. 2, each eccentric artificial local surface plasmon basic unit is a circular grating having a hollow circle therein, so that the geometric center and the center of gravity of the circular grating are offset, that is, the circular grating is an eccentric structure; the width of the edge of the circular grating is b, and the outer radius of the teeth (teeth) of the circular grating is R 2 The number of teeth is N, N is more than 30, so that the grating period is far less than the wavelength of the electromagnetic wave, the grating period is d, the grating duty ratio is a/d, and the radius of the hollow circle is R 1 (ii) a In the embodiment, the deviation of the geometric center is adopted, the teeth of the circular grating are uniformly distributed, and the distance between the center of the hollow circle and the geometric center of the circular grating is delta L; the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, the period of the periodic two-dimensional array is D +2(b + R) 2 )。
In this example, M and N are both 10, R 1 ＝5mm，R 2 15mm, 1mm, 0.4 a/D, 60N, 10mm, and 100 eccentric artificial local surface plasmon basic units.
The implementation method of the high-Q-value eccentric artificial local surface plasmon quasi-BIC super surface comprises the following steps:
1) providing a quasi-BIC super-surface:
a) forming 10 multiplied by 10 eccentric artificial local surface plasmon basic units distributed in a periodic two-dimensional array on a substrate;
b) each eccentric artificial local surface plasmon basic unit is a circular grating with a hollow circle therein, so that the geometric center and the gravity center of the circular grating are offset, namely the circular grating is in an eccentric structure;
c) the width of the edge of the circular grating is b, and the outer radius of the teeth (teeth) of the circular grating is R 2 The number of teeth is N, the grating period is d, N is more than 30, so that the grating period d is far less than the wavelength of incident planar electromagnetic waves, namely the grating period is less than or equal to one tenth of the wavelength of the electromagnetic waves, the grating duty ratio is a/d, and the radius of a hollow circle is R 1 ；
d) The eccentric mode of hollow circle decentraction realizes eccentric structure:
the teeth of the circular grating are uniformly distributed, and the distance between the center of the hollow circle and the center of the circular grating is delta L;
e) the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, and the period of the periodic two-dimensional array is D +2(b + R) 2 )；
2) The normal incidence of a plane electromagnetic wave (TEM) is to the quasi-BIC super surface, namely the wave vector direction of the plane electromagnetic wave is vertical to the quasi-BIC super surface, an equiphase plane is parallel to the quasi-BIC super surface, the electric field E and the magnetic field H of the plane electromagnetic wave are both parallel to the surface, and the electric field direction is parallel to the eccentric displacement direction;
3) in the concentric structure of the circular grating with the geometric center coinciding with the center of gravity, the TE mode of the fundamental mode is used when the planar electromagnetic wave is incident from the front 1,1 Is a resonant Leaky Mode (Leaky Mode) that can be excited, and a higher order Mode (TE) 2,1 And above) is a symmetrically protected BIC mode, which has no normal component in its radiation far field, cannot couple with a planar electromagnetic wave, and cannot be excited; the eccentric structure breaks the symmetry of the concentric structure, so that the radiation far field of the high-order mode generates a normal component, the high-order mode is degenerated into a symmetric protection type quasi BIC mode with a very high Q value, and the high-order mode is excited;
4) in quasi-BIC super-surface of eccentric structure, basic mode TE 1,1 Can still be excited, and the resonant frequency of the resonant circuit has slight change; the number of the high-order modes is multiple, the resonant frequency corresponding to each mode is spaced, and a frequency reference can be provided for the spectrometer; the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing; the smaller the distance delta L between the center of the hollow circle and the center of the circular grating is, the narrower the peak corresponding to the high-order mode is, and the larger the corresponding Q value is.
A super surface with a concentric structure (delta d is 0mm) is simulated, and symmetry protection is verified, so that a high-order mode of an artificial surface plasmon cannot be excited. As can be seen from the transmission and reflection coefficients (FIGS. 3 and 4), only one mode is excited on the concentric structure, and the only peak corresponds to the TE 1,1 Mode, the electric field distribution is shown in fig. 5. TE (TE) 2,1 The above higher order modes are not excited due to the symmetric protection. In the concentric structure that the geometric center of the circular grating is coincident with the gravity center, when the circular grating acts with the plane electromagnetic wave, because the high-order mode is protected symmetrically, the circular grating cannot be coupled with the plane electromagnetic wave, the high-order mode cannot be excited, and only TE can be excited 1,1 Mode, thereby forming a BIC mode.
The eccentric structure breaks the symmetry of the concentric structure, so that a high-order mode is degenerated into a quasi-BIC mode with a high Q value, and the high-order mode is excited; and the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing. As can be seen from the transmission and reflection coefficients (FIGS. 6 and 7), the concentric structure is shown except for the excitation of TE 1,1 Mode, can also excite TE 2,1 The above high-order modes correspond to the three peaks on the right side; reference numerals 1 to 4 in fig. 7 denote 4 patterns, respectively. The peak corresponding to the high-order mode is extremely narrow, which shows that the Q value of the high-order mode is extremely high, and the sensitivity of millimeter wave sensing is improved. Eccentrically-excited TE 2,1 And TE 3,1 The electric field distribution of the higher order mode is shown in fig. 8 and 9.
The following exemplifies that this structure can detect a trace gas by a change in resonance frequency caused by a change in dielectric constant of the medium. In the case where the quasi-BIC super-surface background material with Δ L of 2mm is a gas with a dielectric constant of 1.01, the transmission coefficient and the reflection coefficient are simulated again, and as shown in fig. 10 and 11, reference numerals 1 to 4 in fig. 11 represent 4 modes, respectively.
Finally, it is noted that the disclosed embodiments are intended to aid in further understanding of the invention, but those skilled in the art will appreciate that: various substitutions and modifications are possible without departing from the spirit and scope of this disclosure and the appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.
Claims (8)
1. A high Q-value eccentric artificial local surface plasmon quasi-BIC super surface, comprising: the device comprises a substrate and an eccentric artificial local surface plasmon basic unit; forming M multiplied by N eccentric artificial local surface plasmon basic units distributed in a periodic two-dimensional array on a substrate, wherein M and N are integers more than or equal to 3; wherein each eccentric artificial local surface plasmon basic unit is a circular grating with a hollow circle therein, so that the geometric center and the gravity center of the circular grating are offset, that isThe circular grating is of an eccentric structure; the width of the edge of the circular grating is b, and the outer radius of the teeth of the circular grating is R 2 The number of teeth is N, the grating period is d, N is more than 30, so that the grating period d is far less than the wavelength of the incident plane electromagnetic wave, namely the grating period is less than or equal to one tenth of the wavelength of the plane electromagnetic wave, the grating duty ratio is a/d, and the radius of a hollow circle is R 1 (ii) a There are two eccentric modes to realize the eccentric structure: one is that the hollow circle is not concentric, and the other is that the grating structure is not uniform; in the eccentric mode that the hollow circle is not concentric, the teeth of the circular grating are uniformly distributed, and the distance between the center of the hollow circle and the center of the circular grating is delta L; in the eccentric mode of the uneven grating structure, the center of a hollow circle coincides with the center of a circular grating, but teeth of the circular grating are unevenly distributed, namely one or more parameters of grating constant, duty ratio, spacing and length are unevenly distributed, so that the geometric center and the center of gravity of the circular grating are offset, and the spacing between the geometric center and the center of gravity is delta L; the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, and the period of the periodic two-dimensional array is D +2(b + R) 2 ) (ii) a The plane electromagnetic wave is normally incident to the quasi-BIC super surface, namely the wave vector direction of the plane electromagnetic wave is vertical to the quasi-BIC super surface, the equiphase plane is parallel to the quasi-BIC super surface, the electric field and the magnetic field of the plane electromagnetic wave are both parallel to the surface, and the electric field direction is parallel to the eccentric displacement direction; in the concentric structure of the circular grating with the coincident geometric center and center of gravity, the TE mode of the fundamental mode is adopted when the planar electromagnetic wave is incident from the front 1,1 The high-order mode is a symmetrical protected BIC mode, and a radiation far field of the high-order mode has no normal component, cannot be coupled with plane electromagnetic waves and cannot be excited; the eccentric structure breaks the symmetry of the concentric structure, so that the radiation far field of the high-order mode generates a normal component, the high-order mode is degenerated into a symmetric protection type quasi BIC mode with a very high Q value, and the high-order mode is excited; in quasi-BIC super-surface of eccentric structure, basic mode TE 1,1 Can still be excited, and the resonant frequency of the resonant circuit has slight change; the number of higher-order modes being plural, each mode corresponding to a harmonicThe vibration frequencies are all spaced, and a frequency reference can be provided for the spectrometer; the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing; the smaller the distance delta L between the center of the hollow circle and the center of the circular grating is, the narrower the peak corresponding to the high-order mode is, and the larger the corresponding Q value is.
2. The quasi-BIC super-surface of claim 1, wherein for a quasi-BIC super-surface applied to a microwave frequency band, the substrate employs a printed circuit board; for the quasi-BIC super surface applied to the terahertz frequency band, the substrate is made of silicon dioxide.
3. A quasi-BIC metasurface according to claim 1, wherein the material of the circular grating is a high conductivity metal.
4. The quasi-BIC metasurface of claim 1 wherein the teeth of the circular grating have an outer radius R when the quasi-BIC metasurface operates in the microwave frequency band 2 In the millimeter order; when the quasi-BIC super surface works in the terahertz frequency band, the outer radius R of the teeth of the circular grating 2 On the order of microns.
5. A quasi-BIC metasurface according to claim 1 wherein the width b of the edge of the circular grating, the outer radius R of the teeth of the circular grating 2 Grating duty cycle a/d and radius of the hollow circle and R 1 The following relation is satisfied: r is 2 /4≤R 1 ≤R 2 2; the duty ratio a/d of the grating is 0.2-0.8; r is 2 /20≤b≤R 2 /10。
6. The quasi-BIC super-surface of claim 1, wherein a distance D between adjacent eccentric artificial local surface plasmon base units satisfies: r 2 /4≤D≤2R 2 。
7. The method for realizing the high-Q eccentric artificial local area surface plasmon quasi-BIC super surface of claim 1, wherein the method comprises the following steps:
1) providing a quasi BIC super-surface:
a) forming M multiplied by N eccentric artificial local surface plasmon basic units distributed in a periodic two-dimensional array on a substrate, wherein M and N are integers more than or equal to 3;
b) each eccentric artificial local surface plasmon basic unit is a circular grating with a hollow circle therein, so that the geometric center and the gravity center of the circular grating are offset, namely the circular grating is in an eccentric structure;
c) the width of the edge of the circular grating is b, and the outer radius of the teeth of the circular grating is R 2 The number of teeth is N, the grating period is d, N is more than 30, so that the grating period d is far less than the wavelength of incident planar electromagnetic waves, namely the grating period is less than or equal to one tenth of the wavelength of the electromagnetic waves, the grating duty ratio is a/d, and the radius of a hollow circle is R 1 ；
d) There are two eccentric modes to realize the eccentric structure: one is hollow round non-concentric, and the other is uneven grating structure; the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, the period of the periodic two-dimensional array is D +2(b + R) 2 ）：
i. In the eccentric mode that the hollow circle is not concentric, the teeth of the circular grating are uniformly distributed, and the distance between the center of the hollow circle and the center of the circular grating is delta L;
ii, in an eccentric mode of uneven grating structure, the center of a hollow circle coincides with the center of a circular grating, but teeth of the circular grating are unevenly distributed, namely one or more parameters of grating constant, duty ratio, spacing and length are unevenly distributed, so that the geometric center and the center of gravity of the circular grating are offset, and the spacing between the geometric center and the center of gravity is delta L;
e) the direction of a connecting line between the geometric center and the gravity center of the circular grating is the eccentric displacement direction; the distance between adjacent eccentric artificial local surface plasmon basic units is D, the period of the periodic two-dimensional array is D +2(b + R) 2 ）；
2) The plane electromagnetic wave is normally incident to the quasi-BIC super surface, namely the wave vector direction of the plane electromagnetic wave is vertical to the quasi-BIC super surface, the equiphase plane is parallel to the quasi-BIC super surface, the electric field and the magnetic field of the plane electromagnetic wave are both parallel to the surface, and the electric field direction is parallel to the eccentric displacement direction;
3) in the concentric structure of the circular grating with the coincident geometric center and center of gravity, the TE mode of the fundamental mode is adopted when the planar electromagnetic wave is incident from the front 1,1 The high-order mode is a symmetrical protected BIC mode, and a radiation far field of the high-order mode has no normal component, cannot be coupled with plane electromagnetic waves and cannot be excited; the eccentric structure breaks the symmetry of the concentric structure, so that a radiation far field of a high-order mode generates a normal component, the high-order mode is degenerated into a symmetrical protection type quasi-BIC mode with a high Q value, and the high-order mode is excited;
4) in quasi-BIC super-surfaces of eccentric structure, the basic mode TE 1,1 Can still be excited, and the resonant frequency of the resonant circuit has slight change; the number of the high-order modes is multiple, the resonant frequency corresponding to each mode is spaced, and a frequency reference can be provided for the spectrometer; the peak corresponding to the high-order mode is extremely narrow, namely the high-order mode has an extremely high Q value, which is beneficial to improving the sensitivity of electromagnetic wave sensing; the smaller the distance delta L between the center of the hollow circle and the center of the circular grating is, the narrower the peak corresponding to the high-order mode is, and the larger the corresponding Q value is.
8. The method of claim 7, wherein the quasi-BIC super-surface is placed in a background material, and the trace gas is detected by a change in resonant frequency caused by a change in dielectric constant of a medium of the background material.
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