Single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface

Abstract

The invention discloses a single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface, and relates to the technical field of terahertz electromagnetism. The terahertz metasurface is composed of a plurality of periodically arranged metasurface units; the metasurface unit is of a center rotation symmetrical structure and comprises a metal substrate, a dielectric substrate and a metal patch layer composed of an I-type metal patch and a single branch parasitic patch. By adjusting the size of the metal patch layer, an eight-class metasurface unit with a 45-degree phase gradient is obtained; according to left-handed and right-handed circularly polarized waves of different modals generated according to requirements, eight types of metasurface units are placed at corresponding positions of the terahertz metasurface, and corresponding rotation is carried out based on the eight types of metasurface units, so that the polarization multiplexing terahertz metasurface meeting the requirements is obtained. According to the invention, independent regulation and control of left-handed and right-handed circularly polarized waves are realized by using the same metasurface array in a terahertz frequency band, the vortex wave generation efficiency of the metasurface array is improved, and the complexity of generating vortex waves in any mode is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the field of terahertz electromagnetic technology, and in particular relates to a single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface. Background Art

[0002] Terahertz waves are part of the electromagnetic spectrum between the infrared and microwave bands, with a frequency range from 0.1THz to 10THz, and a corresponding wavelength between 30μm and 3mm. As a transition zone between macroscopic electronics and microscopic optoelectronics, the terahertz wave band has very unique physical and chemical properties. Terahertz waves have great application prospects in high-speed wireless communications, high-resolution imaging and other fields due to their unique advantages, while vortex waves carrying orbital angular momentum can further enhance communication capacity due to their spiral phase and orthogonality. Combining these two technologies is expected to further promote the vigorous development of communications, imaging, sensing and other fields, especially their special role in national defense, military and terahertz communications. Therefore, how to flexibly and efficiently generate the required terahertz vortex wave beams has become a current research hotspot.

[0003] Electromagnetic waves propagating in space can carry energy and momentum at the same time, where momentum includes linear momentum and angular momentum. Linear momentum depends on translation and force, while angular momentum is determined by rotation and torque. Angular momentum is composed of spin angular momentum and orbital angular momentum OAM (Orbital Angular Momentum). When the beam is twisted, the equiphase surface of the electromagnetic wave is spirally distributed, and the OAM mode of the beam is no longer zero. This electromagnetic wave is called a vortex electromagnetic wave. In theory, the OAM mode number of a vortex wave can be any value, and vortex waves with different OAM mode numbers have modal orthogonality. They do not interfere with each other and are orthogonal to each other. This feature also makes vortex waves a new multiplexing technology, providing a new direction for solving the problem of spectrum congestion and shortage in wireless communications and improving communication capacity.

[0004] Research on the generation of vortex electromagnetic waves based on metasurfaces has made significant progress. Metasurfaces use their unique phase control technology to achieve flexible design of the phase, amplitude and polarization of electromagnetic waves. Traditional geometric phase metasurfaces achieve phase mutations of electromagnetic waves by simply changing the rotation angle of the unit, thereby achieving control of the phase gradient, greatly reducing the complexity of designing and processing metasurfaces. However, metasurfaces that rely solely on geometric phase can only provide intrinsic opposite signs for the two spins, resulting in only spin-locking functions (i.e., left-handed and right-handed polarization mirror images) for two circularly polarized lights. When generating vortex waves of different modes, the required metasurface arrays are also different, greatly increasing the complexity of generating arbitrary mode vortex waves. Therefore, it is of great research significance to study how to achieve wavefront control of two arbitrary mode vortex electromagnetic waves under the same metasurface array, that is, polarization multiplexing of metasurfaces. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a terahertz metasurface with single-branch parasitic I-type broadband polarization multiplexing. The metasurface unit proposed in the present invention can achieve left-handed and right-handed circularly polarized waves of different modes under the same circularly polarized incident wave by adjusting the arc radius and arc angle of the I-type metal patch and the length of the parasitic single branch within the terahertz frequency band, thereby realizing the polarization multiplexing function of the metasurface in the terahertz frequency band.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0007] A single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface, comprising a plurality of periodically arranged metasurface units;

[0008] The metasurface unit is a central rotationally symmetrical structure, comprising a metal substrate (1), a dielectric substrate (2) and a metal patch layer (3) arranged in sequence from bottom to top;

[0009] The metal patch layer (3) is composed of an I-type metal patch (31) and a single-branch parasitic patch (32); wherein the I-type metal patch is composed of two symmetrically arranged arc-shaped branches (311) and a rectangular branch (312) connecting the two arc-shaped branches, and the center of the circle corresponding to the arc-shaped branches is located on the midline of the rectangular branch; and the single-branch parasitic patch is a rectangular metal patch vertically loaded on the rectangular branch.

[0010] By adjusting the radius and opening angle of the arc-shaped branches in the metal patch layer (3) and the length of the single-branch parasitic patch, 8 types of metasurface units with a 45° phase gradient are obtained; according to the left-handed and right-handed circularly polarized waves of different modes generated as required, the transmission phase and geometric phase required by the metasurface units at different positions of the terahertz metasurface are obtained, and the 8 types of metasurface units are placed at corresponding positions of the terahertz metasurface, and are rotated accordingly based on the geometric phase, so as to obtain a polarization multiplexing terahertz metasurface that meets the requirements.

[0011] Furthermore, the metasurface unit is applicable to a frequency band ranging from 0.095THz to 0.18THz.

[0012] Furthermore, the period of the metasurface unit is in the range of half a wavelength to a quarter of a wavelength.

[0013] Furthermore, the materials of the metal patch layer (3) and the metal substrate (1) are metal copper; the dielectric substrate (2) is F4B material with a dielectric constant εr=2.65, a thickness h=0.3 mm, and a loss tangent of 0.002.

[0014] Compared with the prior art, the present invention provides a single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface. The metasurface unit is within the frequency band of 0.095THz-0.18THz. By adjusting the parasitic single branch and the I-type metal patch, the 8 types of structural units obtained can achieve a 45° phase gradient, thereby satisfying the 360° transmission phase coverage; at the same time, by rotating the angle of the metal patch layer, a 360° geometric phase coverage can be obtained. By independently regulating the transmission phase and geometric phase of the metasurface unit, the metasurface of the present invention realizes the function of obtaining left-handed and right-handed circularly polarized waves of different modes under the same circularly polarized incident wave in the terahertz frequency band, and realizes the broadband polarization multiplexing function of the terahertz frequency band metasurface. At the same time, the metasurface of the present invention can achieve a co-polarization conversion efficiency of more than 92% within the frequency band of 0.095THz-0.18THz (the mode purity of the generated array is 90%, and the cross-polarization is less than 10%). In addition, the present invention has the characteristics of simple and adjustable structure and low processing cost, and has great application prospects in the field of terahertz communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the present invention are briefly introduced below.

[0016] Figure 1 This is a schematic diagram of the single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface structure;

[0017] Figure 2Schematic diagram of 8 metasurface units obtained after adjusting the parasitic single branch and the radius of the I-type arc structure and the arc angle;

[0018] Figure 3 is the reflection coefficient curve of 8 terahertz metasurface units;

[0019] Figure 4 is the reflection coefficient curve of the terahertz metasurface unit at different rotation angles;

[0020] Figure 5 A top view of a periodic array structure composed of metasurface units;

[0021] Figure 6 Generate a thermal map of the phase and amplitude distribution of polarization-multiplexed vortex waves for the metasurface array at 0.11 THz with left-handed mode l1=+1 and right-handed mode l2=+1;

[0022] Figure 7 A histogram of the purity distribution of vortex wave modes with polarization multiplexing of left-handed mode l1=+1 and right-handed mode l2=+1 is generated for the metasurface array at 0.11 THz. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects and features of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0024] This embodiment provides a single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface, which includes 8×8 periodically arranged metasurface units.

[0025] The metasurface unit has a period length of p = 1 mm and is a central rotationally symmetrical structure, such as Figure 1 As shown, it includes a metal substrate (1), a dielectric substrate (2) and a metal patch layer (3) arranged in sequence from bottom to top. The metal patch layer and the metal substrate are made of copper, and the dielectric substrate is made of F4B material with a dielectric constant εr=2.65, a thickness h=0.3 mm, and a loss tangent of 0.002.

[0026] The metal patch layer (3) is composed of an I-type metal patch (31) and a single-branch parasitic patch (32); wherein the I-type metal patch is composed of two symmetrically arranged arc-shaped branches (311) and a rectangular branch (312) connecting the two arc-shaped branches, and the center of the circle corresponding to the arc-shaped branches is located on the midline of the rectangular branch; and the single-branch parasitic patch is a rectangular metal patch vertically loaded on the rectangular branch.

[0027] By adjusting the radius and opening angle of the arc-shaped branches in the metal patch layer (3), and the length of the parasitic patch of a single branch, the following can be obtained: Figure 2There are 8 metasurface units with a phase gradient of 45° as shown; in this embodiment, the sizes of the 8 metasurface units are: w=0.12mm, r1=0.40mm, d=0.44mm, α=30° in unit ①; r1=0.33mm, d=0.49mm, α=101° in unit ②; r1=0.37mm, d=0.42mm, α=115° in unit ③; r1=0.38mm, d=0.38mm, α=133° in unit ④; the structural parameters of units ⑤⑥⑦⑧ are the same as those of units ①②③④, except that the unit structure is rotated 90°.

[0028] Figure 3 The figure shows the reflection coefficients of the eight terahertz metasurface units in this embodiment. From 0.095 THz to 0.18 THz, the co-polarization coefficients of the eight metasurface units are all above 0.93. At this time, the polarization conversion efficiency (efficiency = r ll 2 / (r ll 2 +r rl 2 )) are all above 92%, meeting a high conversion efficiency. At the same time, within the frequency range, the difference in the transmission phase of the 8 units remains roughly consistent (the difference is about 45°), covering a 360° transmission phase.

[0029] Figure 4 The figure shows the reflection coefficient of the terahertz metasurface unit at different rotation angles in this embodiment. The added phase and the rotation angle strictly satisfy the relationship of two within the entire bandwidth, which verifies the characteristics of the geometric phase and can cover a 360° geometric phase.

[0030] According to the requirements, the left-hand and right-hand circularly polarized waves of different modes are generated, and the transmission phase and geometric phase required by the metasurface units at different positions of the terahertz metasurface are obtained. The eight metasurface units are placed at the corresponding positions of the terahertz metasurface, and are rotated accordingly based on the geometric phase to obtain a polarization multiplexing terahertz metasurface that meets the requirements, such as Figure 5 shown.

[0031] Figure 6 Shown is the phase and amplitude distribution thermogram of the polarization multiplexing of the vortex wave of the left-handed mode l1=+1 and the right-handed mode l2=+1 at 0.11THz generated by the metasurface array in this embodiment, where LH represents the generated left-handed circularly polarized vortex wave, and RH represents the generated left-handed circularly polarized vortex wave; the phase thermogram on the left shows that the obtained left (right) vortex wave has a counterclockwise (clockwise) vortex phase with a period (360°), and the amplitude distribution thermogram on the right is donut-shaped, indicating that left-handed mode l1=+1 and right-handed mode l2=+1 vortex waves are generated.

[0032] Figure 7 Shown is a bar chart of the mode purity of polarization multiplexing of vortex waves with left-handed mode l1=+1 and right-handed mode l2=+1 generated by the metasurface array in this embodiment at 0.11 THz, where the main mode vortex waves with both left and right hand modes generated as +1 account for 88.96% and 86.10%, respectively, indicating that high-purity polarization multiplexing vortex waves have been obtained.

[0033] Compared with the traditional method, the advantages of the present invention are as follows: by adjusting the length of the parasitic single branch, the radius of the I-type arc branch and the arc angle, 8 units with a phase gradient of 45° can be obtained, that is, the metasurface unit of the present invention has the advantages of simple structure and easy adjustment. The unit can achieve a co-polarization conversion efficiency of more than 92% (the mode purity of the array is close to 90%) in the frequency band range of 0.095THz-0.18THz (about 61% relative bandwidth), and has the advantages of broadband and high efficiency. At the same time, the independent regulation of left-handed and right-handed circularly polarized waves by the same metasurface array is realized in the terahertz frequency band, and the design realizes the function of obtaining left-handed and right-handed circularly polarized waves of different modes under the same circularly polarized incident wave in the terahertz frequency band, realizing the broadband polarization multiplexing function of the metasurface in the terahertz frequency band.

Claims

1. A single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface, comprising a plurality of periodically arranged metasurface units; characterized in that: The metasurface unit is a central rotationally symmetrical structure, comprising a metal substrate (1), a dielectric substrate (2) and a metal patch layer (3) arranged in sequence from bottom to top; The metal patch layer (3) is composed of an I-type metal patch (31) and a single-branch parasitic patch (32); wherein the I-type metal patch is composed of two symmetrically arranged arc-shaped branches (311) and a rectangular branch (312) connecting the two arc-shaped branches, and the center of the circle corresponding to the arc-shaped branches is located on the midline of the rectangular branch; the single-branch parasitic patch is a rectangular metal patch vertically loaded on the rectangular branch; By adjusting the radius and opening angle of the arc-shaped branches in the metal patch layer (3) and the length of the single-branch parasitic patch, 8 types of metasurface units with a 45° phase gradient are obtained; according to the left-handed and right-handed circularly polarized waves of different modes generated as required, the transmission phase and geometric phase required by the metasurface units at different positions of the terahertz metasurface are obtained; the 8 types of metasurface units are placed at corresponding positions of the terahertz metasurface, and are rotated accordingly based on the geometric phase, so as to obtain a polarization multiplexing terahertz metasurface that meets the requirements.

2. The single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface according to claim 1, characterized in that: The metasurface unit is suitable for a frequency band ranging from 0.095THz to 0.18THz.

3. The single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface according to claim 2, characterized in that: The period of the metasurface unit is in the range of half wavelength to quarter wavelength.

4. The single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface according to claim 3, characterized in that: The material of the metal patch layer (3) and the metal base (1) is metal copper.

5. The single-branch parasitic I-type broadband polarization multiplexing terahertz metasurface according to claim 4, characterized in that: The dielectric substrate (2) is made of F4B material with a dielectric constant εr=2.65, a thickness h=0.3 mm, and a loss tangent of 0.002.

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