Terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasma

Abstract

The invention discloses a terahertz three-dimensional one-way transmission waveguide based on magnetic surface plasma. The terahertz three-dimensional one-way transmission waveguide is composed of a one-way transmission area and two artificial magnetic conductor layers which are spliced on the left side and the right side of the one-way transmission area and are identical in structure and opposite in direction. The one-way transmission area is of an electrically opaque medium-magnetized semiconductor structure, and the artificial magnetic conductor is formed by a structure that a square metal rod periodically extends in a dielectric background and is arranged on a metal floor; the artificial magnetic conductor can replace an ideal magnetic conductor boundary condition to support three-dimensional unidirectional transmission; the waveguide structure provided by the invention realizes three-dimensional one-way transmission based on magnetic surface plasma under the terahertz wave band, provides a solution for expanding the two-dimensional one-way waveguide to the three-dimensional one-way waveguide, and has great application prospects in the aspect of miniaturization of non-reciprocal devices.

Description

Technical Field

[0001] The present invention relates to the field of terahertz unidirectional waveguides, and in particular to a terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmons. Background Art

[0002] Terahertz waves refer to electromagnetic radiation with a frequency range of 0.1-10 THz. While infrared and microwave technologies on either side of the terahertz band are highly mature in the electromagnetic spectrum, terahertz technology has lagged far behind the established technologies in adjacent bands, creating a so-called "terahertz blank zone." As a result, the development of terahertz technology has lagged significantly. Terahertz waves have the advantage of being minimally destructive to matter and the human body. This band encompasses the characteristic spectra of materials such as semiconductors, plasmas, and biomacromolecules, potentially advancing understanding of fundamental scientific issues in physics, chemistry, and life sciences. Terahertz communications combine the advantages of microwave and optical communications, offering high transmission rates, large capacity, strong directionality, high security, and excellent penetration. They hold particularly promising prospects for military communications and have become a hot topic for exploration and development in various countries. In recent years, while terahertz radiation sources and detection technologies have advanced rapidly, the development of terahertz wave manipulation technologies and related photonic devices has been slower.

[0003] Surface plasmon polaritons (SPPs) are mixed excited states of electrons and photons at the interface between metals and dielectrics that propagate like waves. SPPs can overcome the diffraction limit and confine electromagnetic fields to a range far smaller than the wavelength, achieving so-called subwavelength confinement. This provides an excellent path for miniaturization of photonic devices and high-integration optical systems. However, the plasmon frequencies of metals are typically in the ultraviolet region, making SPPs on metal surfaces only suitable for use in the visible light region. In the terahertz region, corresponding plasmon materials exist: semiconductors. Since semiconductors have plasmon frequencies in the terahertz region, terahertz SPPs on semiconductor surfaces behave similarly to SPPs on metal surfaces (in the visible light region). Using semiconductors, techniques for manipulating SPPs in the visible light region can be directly applied to the terahertz region. Of particular importance is that semiconductors are also gyromagnetic and optical materials. Under the influence of an external magnetic field, the time reversal symmetry of the system is broken, allowing them to support non-reciprocal SPPs, also known as surface magnetic plasmons (SMPs). Based on SMPs, terahertz non-reciprocal photonic devices can be constructed. These terahertz non-reciprocal devices offer advantages such as miniaturization, simple structure, and broadband performance. However, these devices rely on ideal magnetic conductor boundaries and are essentially only two-dimensional devices. Therefore, extending these devices to three dimensions is of great significance.

[0004] Nonreciprocal devices are often essential elements in optical systems. Ideally, they ensure perfect unidirectional signal transmission within the system. In addition to eliminating destructive feedback to the transmitter, they also significantly simplify optical system design by suppressing multipath reflections between devices, significantly improving the system's robustness to manufacturing defects and environmental variations. The rapid development of optical information technology has driven the demand for miniaturization of nonreciprocal photonic devices, leading to the emergence of electromagnetic unidirectional modes (EMPMs), a novel physical concept emerging in this century. A unidirectional EMPM is an EM wave mode that propagates in only one direction. It is immune to backscattering caused by defects (or bends) because there are no counter-propagating modes in the system. Unidirectional EMPMs (USMPs) based on SMPs offer a simple configuration and readily achieve broadband performance. Nonreciprocal devices based on USMPs are also more amenable to miniaturization.

[0005] Furthermore, the application of USMPs in photonic devices requires resolving lateral confinement and realizing three-dimensional waveguide structures. Microwave USMPs based on ferrite materials are E-polarized surface waves, so they can be constructed into three-dimensional waveguides by lateral truncation with a pair of metal plates. These three-dimensional USMPs exhibit the same modal properties as two-dimensional USMPs. However, this approach fails for terahertz USMPs and optical USMPs based on gyroelectric materials. Therefore, achieving lateral confinement of high-frequency USMPs and constructing three-dimensional waveguides remains a critical scientific challenge that needs to be addressed.

[0006] Chinese patent application publication number CN117423996A discloses "A leaky-wave metasurface and method based on a unidirectional electromagnetic mode." It is a unidirectional transmission waveguide structure based on magnetic surface plasmon implemented in the microwave band. The USMP implemented by the ferrite material used is an E-polarized surface wave, so a three-dimensional waveguide can be constructed by lateral truncation of a pair of metal plates. However, this method is ineffective for terahertz USMP (H polarization) and optical band USMP (H polarization) based on gyroelectric materials.

[0007] The Perfect Magnetic Conductor (PMC) boundary condition plays a crucial role in electromagnetic design, particularly in applications such as waveguide design, surface plasmon waveguides, and electromagnetic shielding. The PMC simulates an ideal magnetic surface. When an electromagnetic wave is incident on a PMC surface, the tangential component of the magnetic field is zero. Furthermore, the PMC's reflection of the magnetic field differs from that of the electric field: the electric field's phase is reversed 180 degrees, while the magnetic field's phase shift is 0 degrees. Although the PMC is an idealized model, artificial materials are often used in practical applications to approximate its behavior and meet electromagnetic design requirements.

[0008] Artificial magnetic conductors (AMCs) are typically composed of periodically arranged units that form an artificial electromagnetic material structure on a macroscopic scale. The structural units can be metal, conductive, or other dielectric materials, and are typically designed with specific shapes and dimensions to produce a desired electromagnetic response within a specific frequency band. The periodic structure induces localized resonance of electromagnetic waves, which can produce significant magnetic field effects within a specific frequency range. At high frequencies, the propagation behavior of electromagnetic waves is influenced by the surface structure of the material. When an electromagnetic wave is incident on the surface of an AMC, the interaction between the surface structure and the incident wave results in reflection or transmission characteristics. These structures mimic the behavior of PMCs through resonance or other electromagnetic effects. In the past, AMCs were primarily used to reduce backlobe radiation from microstrip antennas, thereby increasing antenna gain and improving radiation performance. Summary of the Invention

[0009] The present invention aims to overcome the aforementioned shortcomings of the prior art and provides a terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmons. This invention can support terahertz three-dimensional USMPs, providing a solution for expanding such two-dimensional unidirectional waveguides to three-dimensional unidirectional waveguides, and has significant application prospects in the miniaturization of non-reciprocal devices.

[0010] The present invention achieves the above technical objectives through the following technical means, specifically:

[0011] A terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmons consists of a unidirectional transmission region and two artificial magnetic conductor layers with identical structures but opposite directions, spliced ​​to the left and right sides of the unidirectional transmission region. The unidirectional transmission region is a terahertz two-dimensional USMP waveguide structure under PMC boundary conditions, namely an electrically opaque dielectric-magnetized semiconductor structure capable of supporting the terahertz two-dimensional USMP. The artificial magnetic conductor consists of a periodic extension of square metal rods in a dielectric background and placed on a metal floor, simulating the reflection characteristics of an ideal magnetic conductor.

[0012] Preferably, the electrically opaque medium-magnetized semiconductor structure, wherein the electrically opaque medium is along Axis positive direction, The positive direction of the axis extends infinitely;

[0013] The relative dielectric constant of the electrically opaque medium is negative.

[0014] Furthermore, the relative dielectric constant of the electrically opaque medium is .

[0015] Preferably, in the electrically opaque medium-magnetized semiconductor structure, the magnetized semiconductor is in a static magnetic field. In, along Axis positive direction, The negative direction of the axis extends infinitely;

[0016] The direction of the static magnetic field is Positive axis direction.

[0017] Preferably, the unidirectional transmission region is obtained by extending the electrically opaque medium-magnetized semiconductor structure; wherein the electrically opaque medium layer is extended along the Axis positive direction, The magnetized semiconductor layer is extended along the positive direction of the axis. Axis positive direction, The width of the one-way transmission area is w, which is extended in the negative direction of the axis.

[0018] Preferably, the dielectric constant of the electrically opaque medium is The magnetized semiconductor is a rotating electromagnetic material, and under the action of a static magnetic field, its relative dielectric constant tensor is ,in , , ;in is the plasma angular frequency of the magnetized semiconductor, is the electron cyclotron frequency, which is determined by the applied static magnetic field Decide, is the high-frequency relative permittivity of the magnetized semiconductor, and the plasma frequency of the magnetized semiconductor .

[0019] The artificial magnetic conductor of the present invention is composed of a square metal rod periodically extended in a dielectric background and placed on a metal floor; the parameters of the square metal rod are as follows: a = 7.6 is the periodic constant, b=0.8a is the side length of the metal rod, and h=2a is the height of the square metal rod and dielectric. The dielectric constant of the structure is 4, and the metal and metal floor are made of copper.

[0020] The unidirectional transmission region of the present invention is a terahertz two-dimensional USMP waveguide structure under PMC boundary conditions, that is, an electrically opaque medium-magnetized semiconductor structure, which can achieve two-dimensional unidirectional transmission. The transmission direction is Axis positive direction, polarization type is H polarization .

[0021] The artificial magnetic conductor of the present invention is composed of a structure in which a square metal rod is periodically extended in a dielectric background and placed on a metal floor. The artificial magnetic conductor is usually designed with a specific shape and size to generate the required electromagnetic response within a specific frequency band. The local resonance of the electromagnetic wave caused by the periodic structure can produce a significant magnetic field effect within a specific frequency range, simulating the reflection characteristics of the PMC boundary condition. The artificial magnetic conductor of the present invention has a specific shape and size in the working frequency. The reflection characteristics of PMC can be simulated nearby, at the working frequency When , the magnetic field reflection phase is 0, which is applicable to the above-mentioned terahertz two-dimensional USMP waveguide.

[0022] The present invention innovatively applies the characteristics of artificial magnetic conductors to the terahertz two-dimensional USMP waveguide, simulates the reflection characteristics of PMC through artificial magnetic conductors with specific structures, and realizes terahertz three-dimensional USMP.

[0023] The advantages of this invention are that the waveguide structure provides a solution for expanding this type of two-dimensional unidirectional waveguide to three-dimensional unidirectional waveguides. This structure is also applicable to other two-dimensional USMP waveguide structures in the terahertz range and is expected to be extended to optical frequencies, showing significant application prospects in the miniaturization of non-reciprocal devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 3D unidirectional terahertz waveguide according to the present invention.

[0025] Figure 2 yes Figure 1 Top view of .

[0026] Figure 3 yes Figure 1 Left view of .

[0027] Figure 4 It is a structural diagram of the artificial magnetic conductor of the present invention.

[0028] Figure 5 yes Figure 4 Top view of .

[0029] Figure 6 yes Figure 4 Front view of.

[0030] Figure 7 It is the reflection phase diagram of the artificial magnetic conductor of the present invention.

[0031] FIG8( a ) is a schematic diagram of the terahertz two-dimensional unidirectional waveguide transmission with a magnetic field applied according to the present invention, and FIG8( b ) is a schematic diagram of the terahertz two-dimensional unidirectional waveguide transmission without a magnetic field applied according to the present invention.

[0032] FIG9( a ) is a schematic diagram of unidirectional transmission of the terahertz three-dimensional unidirectional waveguide without obstacles of the present invention, and FIG9( b ) is a schematic diagram of unidirectional transmission of the terahertz three-dimensional unidirectional waveguide with obstacles of the present invention.

[0033] Figure 10 This is a dispersion relationship diagram of the terahertz three-dimensional unidirectional waveguide structure of the present invention. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in further detail below.

[0035] Example 1

[0036] First, a 2D THz USMP waveguide was designed under PMC boundary conditions to construct a unidirectional transmission region. Then, an artificial magnetic conductor was designed to simulate the PMC boundary conditions and achieve zero reflection in the magnetic field phase, thus supporting 3D THz USMP.

[0037] First, the unidirectional transmission region and the artificial magnetic conductor unit cell are constructed respectively.

[0038] The one-way transmission area consists of two layers:

[0039] The first layer is an electrically opaque layer, which is an isotropic uniform medium. axis, The positive direction of the axis is infinitely extended, and its relative dielectric constant is , the relative magnetic permeability is 1, and the relative electrical conductivity is 0, such as Figure 1-Figure 3 shown.

[0040] The second layer is a magnetized semiconductor layer. ( The magnetized semiconductor is a gyroelectric anisotropic medium under the action of the positive direction of the axis. axis, The relative dielectric constant tensor is infinitely extended in the negative direction of the axis. ,in , , , the relative magnetic permeability is 1, the relative electrical conductivity is 0, where is the plasma angular frequency of the magnetized semiconductor, is the electron cyclotron frequency, which is determined by the applied static magnetic field Decide, is the high-frequency relative permittivity of the magnetized semiconductor, and the plasma frequency of the magnetized semiconductor ,like Figure 1-3 shown.

[0041] For the above one-way transmission area ( axis, lateral) is cut off with a width of .

[0042] The artificial magnetic conductor unit cell has mirror symmetry and consists of two layers:

[0043] The first layer is composed of square metal rods extended periodically in a dielectric background. The dielectric constant is 4, the relative magnetic permeability is 1, and the relative conductivity is 0. The height of the dielectric and the square metal rods is h=2a, and the period a=7.6 , the side length of the square metal rod is b=0.8a, such as Figure 4-Figure 6 shown.

[0044] The second layer is a metal floor made of copper.

[0045] In the present invention, the unidirectional transmission region is a terahertz two-dimensional USMP waveguide, that is, an electrically opaque medium-magnetized semiconductor structure, which can simulate the waveguide under the PMC boundary conditions. In the case of two-dimensional transmission with infinite extension, the transmission direction is Axis positive direction, polarization type is H polarization The present invention realizes unidirectional transmission under this structure by adjusting the width of w, and the operating frequency is , using a magnetic streamline source (source) to excite, the magnetic field distribution is shown in Figure 8 (a), which is simulated by the commercial simulation software Comsol Multiphysics. When this type of two-dimensional waveguide is extended to a three-dimensional waveguide, The direction needs to be truncated by real materials, which will lead to the generation of non-unidirectional modes, such as conventional modes, and thus lose the unidirectional transmission property. Since the PMC boundary condition does not exist in reality, the application of this type of waveguide is difficult, hindering the development of terahertz wave manipulation technology and related photonic devices. Therefore, finding suitable materials to replace the PMC boundary condition in the above structure is particularly important.

[0046] Based on the above problems, the present invention designs an artificial magnetic conductor to replace the PMC boundary conditions, and designs the parameters of the artificial magnetic conductor unit cell. By adjusting the period constant a, the side length b of the square metal rod, the height h of the square metal rod and the dielectric, and the relative dielectric constant of the dielectric, its performance parameters are made to meet the design. In the present invention, the relative dielectric constant of the dielectric is 4, the relative magnetic permeability is 1, and the relative conductivity is 0. The height of the dielectric and the square metal rod is h=2a, and the period a=7.6 , the side length of the square metal rod is b=0.8a, and the metal rod and the metal floor are both copper, such as Figure 5-7 As shown. The structure works at the frequency nearby( Figure 7 The gray area can simulate the PMC boundary conditions, and its reflection phase diagram is as follows Figure 7 As shown, at the operating frequency When , the reflection phase is 0, and the result is calculated by CST simulation software. In order to verify the transmission characteristics of the designed waveguide structure, the unidirectional transmission area and the artificial magnetic conductor are spliced ​​together to form a terahertz three-dimensional USMP waveguide, and the unidirectional transmission is simulated and verified by the commercial simulation software Comsol Multiphysics. The magnetic field distribution is shown in Figure 9 (a), and the operating frequency is calculated at the same time. The dispersion relation of the neighborhood is further verified numerically to be unidirectional. The results are as follows Figure 10 shown.

[0047] Example 2

[0048] The unidirectional transmission region of Example 1 of the present invention is a terahertz two-dimensional USMP waveguide. Under the influence of a static magnetic field, the system's time reversal symmetry is destroyed, enabling unidirectional transmission. In the absence of an external magnetic field, the unidirectional transmission characteristic is lost, supporting bidirectional transmission. The magnetic field distribution is shown in Figure 8(b).

[0049] Example 3

[0050] Example 1 of the present invention is a terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmons, which is immune to backscattering caused by defects (or bends). In this example, a cylindrical obstacle was added to the waveguide of Example 1 to further observe the unidirectional transmission of the terahertz three-dimensional USMP. The magnetic field distribution is shown in Figure 9(b). The circular obstacle has a diameter of 0.67a and a length of w = 20μm. In this example, the terahertz three-dimensional USMP can perfectly bypass the obstacle and is immune to backscattering caused by defects.

[0051] It should be emphasized that the unidirectional transmission region of the above-mentioned inventive structure is not limited to the waveguide structure of the embodiment, but can also be other terahertz two-dimensional USMP waveguide structures. The artificial magnetic conductor layer is not limited to the structure of the above-mentioned embodiment, but can also be other structures with similar phase reflection characteristics.

[0052] The embodiments described are only preferred embodiments of the present invention and are more universal, and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon, characterized in that: It consists of a unidirectional transmission region and two artificial magnetic conductors with the same structure and opposite directions spliced ​​on the left and right sides of the unidirectional transmission region; the artificial magnetic conductor is composed of square metal rods periodically extended in a dielectric background and placed on a metal floor; the unidirectional transmission region is a terahertz two-dimensional USMP waveguide structure under PMC boundary conditions, that is, an electrically opaque medium-magnetized semiconductor structure, which supports two-dimensional unidirectional transmission based on magnetic surface plasmon under ideal magnetic conductor boundary conditions, and the artificial magnetic conductor replaces the ideal magnetic conductor boundary conditions to support three-dimensional unidirectional transmission.

2. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 1, characterized in that: The electrically opaque medium-magnetized semiconductor structure, wherein the electrically opaque medium is along Axis positive direction, The positive direction of the axis extends infinitely; The relative dielectric constant of the electrically opaque medium is a negative value.

3. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 2, characterized in that: The relative dielectric constant of the electrically opaque medium .

4. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 1, characterized in that: In the electrically opaque medium-magnetized semiconductor structure, the magnetized semiconductor is in a static magnetic field. In, along Axis positive direction, The negative direction of the axis extends infinitely; The direction of the static magnetic field is Positive axis direction.

5. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 4, characterized in that: The magnetized semiconductor is a gyromagnetic optical material. Under the action of a static magnetic field, the relative dielectric constant becomes a tensor with the following form: ,in , , ;in is the plasma angular frequency of the magnetized semiconductor, is the electron cyclotron frequency, determined by the applied static magnetic field Decide, is the high frequency relative permittivity of the magnetized semiconductor, and the plasma frequency of the magnetized semiconductor .

6. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 1, characterized in that: The artificial magnetic conductor is composed of square metal rods periodically extended in a dielectric background and placed on a metal floor, simulating the reflection characteristics of the boundary conditions of an ideal magnetic conductor.

7. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 6, characterized in that: The artificial magnetic conductor has an operating frequency Simulate the reflection characteristics of PMC nearby, at the working frequency When , the magnetic field reflection phase is 0, which is applicable to the above-mentioned terahertz two-dimensional USMP waveguide.

8. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 6, characterized in that: The parameters of the square metal rod are as follows: a=7.6 is the periodic constant, b=0.8a is the side length of the metal rod, h=2a is the height of the square metal rod and the dielectric; the relative dielectric constant of the structural dielectric is 4, and the metal and metal floor materials are copper.

9. The terahertz three-dimensional unidirectional transmission waveguide based on magnetic surface plasmon according to claim 1, characterized in that: The unidirectional transmission region is a terahertz two-dimensional USMP waveguide structure under PMC boundary conditions, which realizes two-dimensional unidirectional transmission. Axis positive direction, polarization type is H polarization .

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