Electromagnetic wave non-reciprocal transmission device and electromagnetic wave non-reciprocal transmission method

Abstract

The present invention discloses an electromagnetic wave non-reciprocal transmission device and an electromagnetic wave non-reciprocal transmission method, the method comprising the following steps: (1) based on a one-dimensional YIG photonic crystal cell, changing the scatterer spacing to generate two basic structural units, namely, Type I with inner near and outer far and Type II with inner far and outer near; (2) adjusting the scatterer spacing to make the two structural band gaps the same, and then combining n Type I cells and n+1 Type II cells to form a parallel plate waveguide, forming a topological interface in the middle; (3) adjusting the lattice constant to couple the boundary states in the waveguide to form a gyromagnetic topological Fano resonance; (4) using the device obtained in steps (1) to (3) to perform electromagnetic wave non-reciprocal transmission; the method not only enriches the research on topological Fano resonance, but also provides a simpler method for achieving electromagnetic wave non-reciprocal transmission with higher contrast.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic wave technology, and in particular to an electromagnetic wave non-reciprocal transmission device and an electromagnetic wave non-reciprocal transmission method. Background Art

[0002] Fano resonance is a widespread wave scattering phenomenon that is common in scientific research and engineering, such as condensed matter physics, electronic circuits, acoustics, electromagnetism, photonics, and nonlinear optics. In optics, the coupling of the bright field state and the dark field state of light can form a Fano resonance, which is manifested as a Fano curve with sharp asymmetric characteristics in the transmission spectrum of light. The transmittance of the Fano curve will change greatly within a narrow frequency range, and its extinction ratio R ER The absolute value of (the ratio of the minimum transmittance to the maximum transmittance) is often more than twice that of the traditional symmetric Lorentz curve. Therefore, Fano resonance has higher sensitivity than traditional Lorentz resonance and is more advantageous in research and application such as optical sensors. However, due to its highly sensitive sensing characteristics, the Fano curve line shape formed by Fano resonance can be easily destroyed by tiny geometric defects in the optical system. In order to solve this problem, researchers have introduced the concept of topology into Fano resonance to improve its resistance to system geometric defects. Topology is a discipline that studies the properties of geometric figures or spaces that remain unchanged after continuous deformation. Topology only considers the position changes between neighbors and ignores the shape changes. Therefore, as long as the topological boundary states formed in the topological structure are used as bright and dark field states and coupled to form topological Fano resonance, the protection characteristics of topology for boundary states can be introduced into Fano resonance, and the Fano curve line shape formed by it will also have a higher immunity to the geometric defects of the system.

[0003] Non-reciprocal transmission means that electromagnetic waves are only allowed to propagate in one direction, while propagation in the opposite direction will be suppressed to a certain extent. This is very similar to the unidirectional conductivity of electronic diodes, so it has broad application prospects in the fields of photon integration, laser technology, and all-optical information processing. At present, researchers have proposed a variety of materials that can realize non-reciprocal transmission of electromagnetic waves, such as non-Hermitian metamaterials, magneto-optical materials, tunable liquid crystal materials, and irreversible loss materials. Among them, the non-reciprocal transmission of magneto-optical materials is the earliest and most widely studied. A typical example is Faraday materials. The magnetic permeability or dielectric constant of Faraday materials is anisotropic and can be expressed in matrix form. The non-diagonal terms in the matrix are antisymmetric imaginary numbers. This type of material breaks the time reversal symmetry and has the characteristics of lossless irreversibility. If the mirror symmetry is broken at the same time, the interface state formed by the electromagnetic wave vector in the forward and reverse directions will no longer be symmetrical, and non-reciprocal transmission can be achieved. However, the current architectures that can achieve non-reciprocal transmission of electromagnetic waves are mostly very complex, and the contrast ratio of non-reciprocal transmission of forward and reverse electromagnetic waves is not high enough, which is not conducive to practical applications. Therefore, it is very important to find a method with a simple architecture and the ability to achieve high-contrast non-reciprocal transmission. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a device for non-reciprocal transmission of electromagnetic waves with high contrast; the purpose of the present invention is to provide a method for non-reciprocal transmission of electromagnetic waves.

[0005] Technical solution: An electromagnetic wave non-reciprocal transmission device of the present invention comprises a parallel plate waveguide of a topological structure, wherein the parallel plate waveguide of the topological structure is composed of a parallel plate waveguide and a magnetic field applied to the parallel plate waveguide, and the lattice constant of the parallel plate waveguide is adjusted to form a gyromagnetic topological Fano resonance, wherein the gyromagnetic topological Fano resonance is formed by coupling of two different boundary states generated between the band gaps of the parallel plate waveguide;

[0006] The parallel plate waveguide is composed of a one-dimensional single-layer photonic crystal; the one-dimensional single-layer photonic crystal is composed of n sequentially distributed Type I cells and n+1 sequentially distributed Type II cells, which are spliced ​​and combined left and right. For Type I cells, the distance between two scatterers in a cell is recorded as d1, and the distance between adjacent scatterers between cells is recorded as d2; for Type II cells, the distance between two scatterers in a cell is recorded as d3, and the distance between adjacent scatterers between cells is recorded as d4; wherein d1=d4 and d2=d3;

[0007] The magnetic field is applied perpendicular to the plane of the scattering substructure to change the magnetic permeability of the one-dimensional single-layer photonic crystal into a gyromagnetic form. The Type I and Type II cells have exactly the same band structure. n Type I cells and n+1 Type II cells are spliced ​​and combined left and right to form a parallel plate waveguide with a topological structure.

[0008] As a further improvement of the above scheme, each unit cell in the one-dimensional single-layer photonic crystal is composed of two scatterers; in the Type I cell: the distance d1 between the two scatterers in the cell is smaller than the distance d2 between adjacent scatterers between the cells;

[0009] The Type II cell: the distance d3 between two scatterers in the cell is greater than the distance d4 between adjacent scatterers between the cells.

[0010] As a further improvement of the above scheme, under the action of the magnetic field, the magnetic field strength is 1600 Gauss, the magnetic permeability of the material scatterers is in the gyromagnetic form, and its matrix form is:

[0011]

[0012] Among them, μ=14μ0, κ=12.4μ0, its dielectric constant is ε=15ε0, the width between its upper and lower hard boundaries is h=14.8cm, and the YIG scatterer radius is 2.67cm.

[0013] Preferably, the parallel plate waveguide lattice constants are a=18 cm, d1=6.6 cm.

[0014] As a further improvement of the above solution, the material of the photonic crystal is a material with gyromagnetic properties.

[0015] Preferably, the material of the photonic crystal is yttrium iron garnet.

[0016] Preferably, the upper and lower boundaries of the parallel plate waveguide use ideal electrical conductors as hard boundaries.

[0017] In another aspect, the present invention provides a method for non-reciprocal transmission of electromagnetic waves, the method comprising the following steps:

[0018] (1) Based on a one-dimensional single-layer photonic crystal cell, the spacing between scatterers is changed to produce two basic structural units: Type I with inner near and outer far and Type II with inner far and outer near;

[0019] (2) Adjust the distance between scatterers to make the band gaps of the two structures the same, and then combine n Type I cells and n+1 Type II cells to form a parallel plate waveguide, forming a topological interface in the middle;

[0020] (3) adjusting the lattice constant so that the boundary states in the waveguide are coupled to form gyromagnetic topological Fano resonance;

[0021] (4) Using the device obtained in steps (1) to (3) to perform non-reciprocal transmission of electromagnetic waves.

[0022] Wherein, the step (1) specifically comprises: based on a parallel plate waveguide of a one-dimensional single-layer photonic crystal, every two scatterers form a unit cell, and the spacing between the scatterers is changed to generate two basic structural units with different topological states:

[0023] Type I: The distance d1 between two scatterers in a cell is smaller than the distance d2 between adjacent scatterers in the cell.

[0024] Type II: The distance d3 between two scatterers in a cell is greater than the distance d4 between adjacent scatterers between cells.

[0025] Wherein, the step (2) specifically includes: applying a magnetic field perpendicular to the structural plane at all scatterers to change the magnetic permeability of the scatterer material into a gyromagnetic form, and then adjusting the internal scatterer spacings of Type I and Type II photonic crystal cells respectively to make the scatterer spacing d1 in the Type I cell equal to the spacing d4 between adjacent scatterers in the Type II cell, and the scatterer spacing d3 in the Type II cell equal to the spacing d2 between adjacent scatterers in the Type I cell, so that the two types of photonic crystals have exactly the same energy band structure; the left side of the parallel plate waveguide is composed of n Type I structure photonic crystal cells arranged horizontally, and the right side is composed of n+1 Type II structure photonic crystal cells arranged horizontally, the upper and lower boundaries use ideal electrical conductors as hard boundaries, and the middle is a topological interface formed by the two structures, which will generate boundary states when electromagnetic waves propagate.

[0026] The present invention designs a one-dimensional parallel plate waveguide based on YIG photonic crystal material and topological Fano resonance, and utilizes the gyromagnetic properties of YIG to realize gyromagnetic topological Fano resonance. It not only has a simple design structure and is resistant to defects, but also can retain the high-sensitivity sensing characteristics of Fano resonance, making it possible to achieve non-reciprocal transmission of electromagnetic waves with higher contrast.

[0027] The present invention explores the gyromagnetic topological Fano resonance of one-dimensional YIG photonic crystals and its characteristics of achieving non-reciprocal transmission of electromagnetic waves with high contrast. The study found that when a photonic crystal with gyromagnetic permeability is used as a scatterer and two one-dimensional cellular structures with different topological states are spliced ​​to form a parallel plate waveguide, the topological boundary state generated at the interface can form a gyromagnetic topological Fano resonance, which appears as a sharp asymmetric Fano curve in the transmission spectrum. Subsequently, electromagnetic waves are obliquely incident from the left and right ports of the waveguide, and then received from the other port and the transmission spectrum of the electromagnetic waves is calculated. By comparing the Fano curves in the transmission spectra in the forward and reverse directions, it is found that there is a transmittance difference of up to about 50 dB, and the absolute value of the extinction ratio of the Fano curve differs by 1.79 times, which verifies its non-reciprocal electromagnetic wave transmission with high contrast.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: topological Fano resonance and electromagnetic wave non-reciprocal transmission are realized in photonic crystals with gyromagnetic properties. The gyromagnetic topological Fano resonance is formed by topological boundary states as bright field states and dark field states. The non-reciprocal transmission of electromagnetic waves is caused by the breaking of time reversal symmetry of the magnetic field and the breaking of mirror symmetry by oblique incidence. This discovery enriches the research on topological Fano resonance and provides a simpler method for realizing high-contrast electromagnetic wave non-reciprocal transmission. The research results of the present invention will have guiding significance for the design of related optical devices such as high-sensitivity optical sensors and optical unidirectional transmission devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A one-dimensional photonic crystal with two YIG scatterers as unit cells arranged periodically in the horizontal direction and its partial energy band diagram, which includes three different basic structural units: (a) Type I: inside-near and outside-far type (d2 / d1>1); (b) all scatterers are equally spaced (d5 / d6=1); (c) Type II: inside-far and outside-near type (d4 / d3<1); the three units have the same lattice constant a and the same upper and lower plate spacing h; (d) partial energy bands of Type I structure; (e) corresponding energy bands when all scatterers are equally spaced; (f) partial energy bands of Type II structure.

[0030] Figure 2 Parallel plate waveguide and its band structure: (a) A parallel plate waveguide formed by splicing three Type I cells and four Type II cells together; (b) A comparison of the band structures when the lattice constant a is 21.5 cm, 20 cm, and 18 cm, respectively.

[0031] Figure 3The positions of the boundary states in the energy band structure and transmission spectrum corresponding to different lattice constants: (a) The positions of the bright field state and the dark field state in the band gap when the lattice constant a=21.5cm; (b) The transmission spectrum when the lattice constant a=21.5cm, the shaded part corresponds to the band gap range in the energy band structure; (c) The positions of the bright field state and the dark field state in the band gap when the lattice constant a=20cm; (d) The transmission spectrum when the lattice constant a=20cm, the shaded part corresponds to the band gap range in the energy band structure; (e) The position of the resonant state formed by the coupling of the bright field state and the dark field state when the lattice constant a=18cm; (f) The transmission spectrum of the band gap between the two middle energy bands when the lattice constant a=18cm, the figure forms a Fano resonance curve; (g) The electric field distribution at the Fano resonance peak (frequency is 1.1171GHz) formed in Figure (f).

[0032] Figure 4 Parallel plate waveguide with lattice constant a = 18 cm and the transmission spectrum of electromagnetic waves obliquely incident from its left and right ports: (a) Figure 2 The parallel plate waveguide structure in the figure has a lattice constant of a = 18 cm. The arrow indicates that the incident direction of the electromagnetic wave is 45° clockwise from the normal incident direction. (b) is the transmission spectrum of the waveguide in the figure (a) with left and right oblique incidence. The extinction ratio R ER左 =-109.1dB, right incident extinction ratio R ER右 =-60.9dB. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0034] An embodiment of the present invention provides an electromagnetic wave non-reciprocal transmission device, which includes a parallel plate waveguide with a topological structure, wherein the parallel plate waveguide with the topological structure is composed of a parallel plate waveguide and a magnetic field applied to the parallel plate waveguide; the lattice constant of the parallel plate waveguide is adjusted so that two different boundary states are generated between the band gaps of the parallel plate waveguide, and the boundary states are coupled as a bright field state and a dark field state to form a gyromagnetic topological Fano resonance.

[0035] The parallel plate waveguide is composed of a one-dimensional single-layer photonic crystal; the one-dimensional single-layer photonic crystal is composed of three sequentially distributed Type I cells and four sequentially distributed Type II cells, which are spliced ​​together on the left and right. Type I cells: the distance between two scatterers in a cell is recorded as d1, and the distance between adjacent scatterers between cells is recorded as d2; Type II cells: the distance between two scatterers in a cell is recorded as d3, and the distance between adjacent scatterers between cells is recorded as d4; wherein d1=d4 and d2=d3.

[0036] The magnetic field is applied perpendicular to the plane of the scattering substructure to change the magnetic permeability of the one-dimensional single-layer photonic crystal into a gyromagnetic form. The two types of cells have exactly the same band structure. n Type I cells and n+1 Type II cells are spliced ​​together left and right to form a parallel plate waveguide with a topological structure.

[0037] Each unit cell in the one-dimensional single-layer photonic crystal is composed of two scatterers; in the Type I cell, the distance d1 between two scatterers in the cell is smaller than the distance d2 between adjacent scatterers between cells;

[0038] The Type II cell: the distance d3 between two scatterers in the cell is greater than the distance d4 between adjacent scatterers between the cells.

[0039] The embodiment of the present invention provides a method for realizing non-reciprocal transmission of electromagnetic waves using the above device, comprising the following steps:

[0040] Step 1: Based on the parallel plate waveguide of one-dimensional YIG photonic crystal, every two scatterers form a unit cell, and the spacing between the scatterers is changed to generate

[0041] Type I: The distance between two scatterers in a cell is smaller than the distance between adjacent scatterers between cells.

[0042] Type II: The distance between two scatterers in a cell is greater than the distance between adjacent scatterers between cells.

[0043] Two basic building blocks with different topological states;

[0044] Step 2: Apply a magnetic field perpendicular to the structural plane at all YIG scatterers to change the magnetic permeability of the YIG material into a gyromagnetic form, and then adjust the internal scatterer spacing of the Type I and Type II photonic crystal cells to the spacing of the scatterers in the Type I cell equal to the spacing of the adjacent scatterers between the Type II cells, and the spacing of the scatterers in the Type II cell equal to the spacing of the adjacent scatterers between the Type I cells. At this time, the two types of photonic crystals have exactly the same band structure. Then, three Type I photonic crystal cells and four Type II photonic crystal cells are spliced ​​together to form a parallel plate waveguide. Because the left and right structures are in different topological states but have the same band structure, a topological boundary state will be formed in the same band gap, which is manifested in the transmission spectrum as obvious transmission peaks and valleys within the band gap frequency range.

[0045] Step 3: To further explore whether the gyromagnetic topological Fano resonance can be formed by the topological boundary state generated by the parallel plate waveguide obtained in step 2, the transmission spectrum of the parallel plate waveguide obtained in step 2 is calculated. The peaks and valleys in the transmission spectrum prove that it has generated boundary states in the middle of the band gap that can be used as the bright field state and dark field state of the Fano resonance, and the electric field distribution at the transmission peak verifies that it is indeed a topological boundary state generated at the junction of the two side structures. By adjusting the unit cell lattice constant of this structure until the peaks and valleys in the band gap are coupled together as bright and dark field states, and calculating its transmission curve, it is found that it forms a Fano resonance curve with sharp asymmetric characteristics, proving the feasibility of YIG parallel plate waveguide to achieve gyromagnetic topological Fano resonance.

[0046] Step 4: Verify whether the YIG gyromagnetic topology Fano resonance can achieve non-reciprocal transmission. Construct a parallel plate waveguide in the simulation in the same arrangement as in Step 2 and Step 3. In order to break the mirror symmetry with the horizontal axis, use an oblique incident direction of the electromagnetic wave that is 45° clockwise from the horizontal normal incident direction. First, inject the electromagnetic wave from the left port of the waveguide, receive the electromagnetic wave from the right port, and calculate the transmission curve; then inject the same electromagnetic wave from the right port of the waveguide, receive the electromagnetic wave from the left port, calculate the transmission curve, and compare the two transmission curves. It is found that there is a significant difference in the Fano resonance curve, which proves that the YIG gyromagnetic topology Fano resonance can achieve non-reciprocal transmission of electromagnetic waves.

[0047] The present invention provides a method for realizing non-reciprocal transmission of electromagnetic waves by using gyromagnetic topological Fano resonance of one-dimensional YIG photonic crystal. Two different topological state structures are used to form a topological interface in the parallel plate waveguide of YIG photonic crystal, and a magnetic field perpendicular to the plane is applied at the scatterer to change the magnetic permeability of YIG into a gyromagnetic form, thereby breaking the time inversion symmetry, and then finding a suitable band gap in the energy band, using the boundary state generated by the topological structure in the band gap as a bright and dark field state for coupling to form gyromagnetic topological Fano resonance, and then obliquely incident the left and right electromagnetic waves to draw the transmission spectrum, and comparing the Fano resonance curves in the positive and negative directions to find obvious differences. The specific embodiments are as follows:

[0048] The three structures of one-dimensional YIG photonic crystals are as follows: Figure 1 The two different topological structures in the one-dimensional YIG photonic crystal parallel plate waveguide are shown in Figure 2. Figure 1 (b) The structure of the equally spaced YIG scatterers shown in Figure 1 is changed. Its basic structure is to set a YIG cylinder as a scatterer at the middle line of the air background, and use an ideal conductor as the upper and lower hard boundaries. Two YIG scatterers are used as a unit cell, and the left and right periodic extensions form a one-dimensional YIG photonic crystal. Since YIG is a material with gyromagnetic properties, the magnetic permeability will change to a gyromagnetic form under an external magnetic field. Therefore, applying a magnetic field perpendicular to the structural plane at each YIG can make the magnetic permeability of YIG anisotropic, which can be expressed by a matrix:

[0049]

[0050] (1) In the formula, represents the magnetic permeability matrix. When the external magnetic field is 1600 Gauss, μ=14μ0, κ=12.4μ0, i is the imaginary unit, and μ0 is the vacuum permeability.

[0051] Assume that the lattice constant is a = 21.5 cm, the upper and lower width is h = 14.8 cm, the YIG scatterer radius is 2.67 cm, the dielectric constant is ε = 15ε0, ε0 is the dielectric constant in vacuum, and the magnetic permeability is the gyromagnetic matrix in formula (1). Next, by adjusting the distance between the centers of the circles, two structures with different topological states are formed: Type I and Type II. Figure 1 As shown in (e), by calculating the band structure of YIG scatterers with equal spacing, it is found that the band gaps between the four bands near 1.11 GHz are basically closed, at this time d5 = d6 = 10.25 cm; then shorten the center distance to Figure 1 (a), it is found that the energy band will open (e.g. Figure 1 (d) shows a band gap in the middle; if the center distance is increased to Figure 1 (c), the corresponding energy band will also open (e.g. Figure 1 (f) and Figure 1 The band structures in (d) are the same. At this time, the change from Type I to Type II can be regarded as a process in which the band changes from open to closed and then open again, that is, the band flips, so the structures of the two are in different topological phases, but have exactly the same band structure.

[0052] Next, take three cells of Type I and four cells of Type II, and splice them together to form a Figure 2 The parallel plate waveguide shown in (a) forms a topological interface in the middle. When the transmission spectrum of the waveguide is calculated within the selected frequency range, it can be found that transmission peaks and valleys appear in the band gap (such as Figure 3 (as shown in (b)), this is the topological boundary state generated by the topological structure.

[0053] Depend on Figure 3 (b) It can be seen that two edge states are formed in the band gap of the four energy bands, where the edge state with high transmittance is the bright field state, and the edge state with low transmittance is the dark field state. Figure 2 As shown in (b), the four energy bands are divided into two groups. The upper and lower two are wide energy bands with a large dispersion degree, and the middle two are narrow energy bands with a very small dispersion degree, which are close to flat bands. By adjusting the lattice constant of the unit cell, the frequency range of these four energy bands and the corresponding waveguide transmission spectrum are calculated respectively. Figure 2 (b) It can be seen that the position and width of the wide band group change significantly, while the position and width of the narrow band group remain almost unchanged. At the same time, it can be seen that the bright field state position will move up significantly with the change of the wide band group, while the dark field state position remains almost unchanged due to the fixation of the narrow band group (e.g. Figure 3 (a)(c)(e)). Therefore, in the process of changing the lattice constant, the position of the dark field state is almost fixed, and the position of the bright field state will move significantly. In this way, this characteristic can be used to continuously shorten the relative distance between the bright and dark field states until the two are coupled to form a Fano resonance. Adjust the lattice constant of the cell to a = 18cm, and the center distance of the scattering sub-circles in the Type I structure cell on the left is d1 = 6.6cm. At this time, the bright and dark field states are coupled in the band gap between the narrow energy band groups to form a Fano resonance curve with sharp asymmetric characteristics (such as Figure 3 (e)(f)), the electric field distribution at the resonance peak is as follows Figure 3 As shown in (g), it can be seen that a quadrupole resonance field is formed at the topological boundary. So far, the gyromagnetic topological Fano resonance has been successfully realized in the gyromagnetic material YIG photonic crystal waveguide using the topological boundary state.

[0054] The present invention uses YIG material with gyromagnetic properties as a scatterer to design a parallel plate waveguide, and realizes gyromagnetic topological Fano resonance under an external magnetic field. The magnetic field will break the time inversion symmetry. If the mirror symmetry is broken at the same time, the YIG photonic crystal parallel plate waveguide in the present invention can achieve a certain degree of non-reciprocal transmission. In the above-mentioned waveguide that realizes Fano resonance, the electromagnetic wave is incident obliquely from the left and right ports respectively, and the left and right ports are incident at an angle of 45° clockwise from the normal incident direction (such as Figure 4 (a) shows that the two transmission curves are plotted and compared, and it is found that there are obvious differences in the sharp Fano curve line shape, such as Figure 4 As shown in (b), the peak transmittance of the Fano curve generated by the two side incidences differs by about 3dB, and the valley transmittance differs by about 50dB. The extinction ratio R ER About -109.1dB, right incident Fano curve extinction ratio R ER About -60.9dB, left and right extinction ratio R ER The absolute value difference is about 1.79 times, and the other parts of the curve differ by about 3 to 6 dB, which proves that the YIG gyromagnetic topological Fano resonance can achieve high-contrast non-reciprocal transmission of electromagnetic waves.

[0055] In summary, the present invention provides a method for realizing gyromagnetic topological Fano resonance and non-reciprocal transmission of electromagnetic waves with high contrast ratio by using a one-dimensional topological structure YIG photonic crystal parallel plate waveguide. The present invention is based on a one-dimensional YIG photonic crystal double scatterer cell structure, and realizes two different topological states by adjusting the spacing between scatterers inside the cell, and then splices the two topological structures to form a topological interface to generate a topological boundary state, and then changes the magnetic permeability of YIG into a gyromagnetic form by applying a magnetic field to break the time reversal symmetry of the waveguide, and then adjusts the lattice constant to couple the topological boundary states to form a gyromagnetic topological Fano resonance. Since the time reversal symmetry of the waveguide is broken by the magnetic field, the oblique incident electromagnetic wave breaks the mirror symmetry, which will cause a certain non-reciprocity in the transmission of the electromagnetic wave, and the high-sensitivity sensing characteristics of the Fano resonance curve will amplify the contrast of the non-reciprocity, which is manifested in the transmission spectrum as the two Fano line types in the left / right transmission curve have a relatively obvious difference, such as the left and right extinction ratio R ER The absolute value differs by 1.79 times, which is a simple method to achieve non-reciprocal transmission of electromagnetic waves with higher contrast, and also provides a reference for the research and application of topological Fano resonance.

[0056] The above content is only a detailed description of the present invention in combination with a specific technical solution, and it cannot be determined that the specific implementation of the present invention is limited to the above description. For technical personnel in the field to which the present invention belongs, without departing from the spirit and scope of the technical solution of the present invention, modifications and equivalent replacements made to the technical solution of the present invention are all covered within the protection scope of the present invention.

Claims

1. An electromagnetic wave non-reciprocal transmission device, characterized in that: The device comprises a parallel plate waveguide of a topological structure, wherein the parallel plate waveguide of the topological structure is composed of a parallel plate waveguide and a magnetic field applied to the parallel plate waveguide, and the lattice constant of the parallel plate waveguide is adjusted to form a gyromagnetic topological Fano resonance, wherein the gyromagnetic topological Fano resonance is formed by coupling of two different boundary states generated between the band gaps of the parallel plate waveguide; The parallel plate waveguide is composed of a one-dimensional single-layer photonic crystal; the one-dimensional single-layer photonic crystal is composed of n sequentially distributed Type I cells and n+1 sequentially distributed Type II cells, which are spliced ​​and combined left and right. For Type I cells, the distance between two scatterers in a cell is recorded as d1, and the distance between adjacent scatterers between cells is recorded as d2; for Type II cells, the distance between two scatterers in a cell is recorded as d3, and the distance between adjacent scatterers between cells is recorded as d4; Wherein, d1= d4 and d2= d3; wherein each unit cell in the one-dimensional single-layer photonic crystal is composed of two scatterers; wherein the Type I cell: the spacing d1 between two scatterers in the cell is smaller than the spacing d2 between adjacent scatterers between the cells; The Type II cell: the distance d3 between two scatterers in the cell is greater than the distance d4 between adjacent scatterers between cells; The magnetic field is applied perpendicular to the plane of the scattering substructure to change the magnetic permeability of the one-dimensional single-layer photonic crystal into a gyromagnetic form. The Type I and Type II cells have exactly the same band structure. n Type I cells and n+1 Type II cells are spliced ​​and combined left and right to form a parallel plate waveguide with a topological structure.

2. The electromagnetic wave non-reciprocal transmission device according to claim 1, characterized in that: The material of the photonic crystal is a material with gyromagnetic properties.

3. The electromagnetic wave non-reciprocal transmission device according to claim 1, characterized in that: The material of the photonic crystal is iron yttrium garnet.

4. The electromagnetic wave non-reciprocal transmission device according to claim 1, characterized in that: The upper and lower boundaries of the parallel plate waveguide use ideal electric conductors as hard boundaries.

5. A method for non-reciprocal transmission of electromagnetic waves, characterized in that: The method comprises the following steps: (1) Based on a one-dimensional single-layer photonic crystal unit cell, by changing the distance between scatterers, two basic structural units are generated: Type I with inner near and outer far and Type II with inner far and outer near. Based on a parallel plate waveguide of a one-dimensional single-layer photonic crystal, every two scatterers form a unit cell. By changing the distance between the scatterers, two basic structural units with different topological states are generated: Type I: The distance d1 between two scatterers in a cell is smaller than the distance d2 between adjacent scatterers in the cell. Type II: The distance d3 between two scatterers in a cell is greater than the distance d4 between adjacent scatterers between cells; (2) Adjust the distance between scatterers to make the band gaps of the two structures the same, and then combine n Type I cells and n+1 Type II cells to form a parallel plate waveguide, forming a topological interface in the middle; (3) Adjusting the lattice constant to couple the boundary states in the waveguide to form gyromagnetic topological Fano resonance; (4) Using the device prepared in steps (1) to (3) to perform non-reciprocal transmission of electromagnetic waves.

6. The method for non-reciprocal electromagnetic wave transmission according to claim 5, characterized in that: Step (2) specifically includes: applying a magnetic field perpendicular to the structural plane at all scatterers to change the magnetic permeability of the scatterer material into a gyromagnetic form, and then adjusting the internal scatterer spacings of Type I and Type II photonic crystal cells respectively so that the scatterer spacing d1 in the Type I cell is equal to the spacing d4 between adjacent scatterers in the Type II cell, and the scatterer spacing d3 in the Type II cell is equal to the spacing d2 between adjacent scatterers in the Type I cell, so that the two types of photonic crystals have exactly the same energy band structure; the left side of the parallel plate waveguide is composed of n Type I structure photonic crystal cells arranged horizontally, and the right side is composed of n+1 Type II structure photonic crystal cells arranged horizontally, the upper and lower boundaries use ideal electrical conductors as hard boundaries, and the middle is a topological interface formed by the two structures, which will generate boundary states when electromagnetic waves propagate.

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