Graphene tunable broadband terahertz polarization converter and application thereof

Abstract

The application discloses a graphene adjustable wideband terahertz polarization converter and application thereof, which comprises a plurality of adjustable polarization conversion units arranged in a rectangular array in the same plane; according to a three-dimensional coordinate system, the adjustable polarization conversion unit comprises a metal grating layer, a dielectric substrate layer, an upper graphene grating layer, a silicon dioxide film isolation layer, a lower graphene grating layer and a direct current voltage source which are sequentially and overlappedly arranged along the z-axis direction from top to bottom and are parallel to the x-axis; the metal grating layer is composed of two rectangular metal sheets of the same size which are equidistantly arranged; the graphene grating layers are each composed of four equidistantly distributed graphene of the same width, and the graphene grating forms a 45° angle with the x-axis; the upper graphene grating layer and the lower graphene grating layer are respectively connected to the positive and negative poles of the direct current voltage source, and the graphene Fermi energy level is controlled by adjusting the bias voltage. The application can realize dynamic regulation and control of terahertz wave polarization, and has the characteristics of tunability, wide working frequency band, high polarization conversion rate and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of terahertz wave polarization converters, and particularly relates to a graphene adjustable broadband terahertz polarization converter and application thereof. BACKGROUND

[0002] Terahertz waves refer to electromagnetic waves between a microwave millimeter wave and an infrared visible light, and the frequency is in the range of 0.1-10 THz. Terahertz technology can be widely applied to military, remote sensing, high-security data communication and transmission, atmospheric and environmental monitoring, real-time biological information extraction, medical diagnosis and other fields.

[0003] Metamaterials refer to a kind of artificial composite materials with special properties. These materials are not found in nature and are periodic or non-periodic composites. They have some special properties, such as negative refractive index, negative permittivity, negative magnetic permeability, etc. Such properties cannot be achieved by traditional materials. The designed metamaterials can effectively regulate and control terahertz waves.

[0004] Most of the current adjustable polarization converters of metamaterials mainly realize the conversion of orthogonal polarized waves, and other types of polarization rotation are less. In some communication systems, 45° polarized waves are necessary, and in some specific cases, this polarization has more advantages than 0° or 90° polarization, such as symmetric propagation characteristics. For some terahertz wave transmitters, the system also needs 45° linear polarization output. Therefore, it is necessary to design an adjustable 45° polarization converter with application requirements. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a graphene adjustable broadband terahertz polarization converter and application thereof, which has the characteristics of tunable, wide working frequency band, high polarization conversion rate, simple structure and the like.

[0006] The application is realized by the following technical solutions:

[0007] The graphene adjustable broadband terahertz polarization converter comprises a plurality of adjustable polarization conversion units arranged in a rectangular array in the same plane; according to a three-dimensional coordinate system, the adjustable polarization conversion unit comprises a metal grating layer, a dielectric substrate layer, an upper graphene grating layer, a silicon dioxide film isolation layer, a lower graphene grating layer and a direct current voltage source which are sequentially and overlappedly arranged along the z-axis direction and parallel to the x-axis.

[0008] The metal grating layer is composed of two equidistantly arranged rectangular metal pieces; the upper graphene grating layer and the lower graphene grating layer have the same structure and are both composed of two small-size trapezoidal graphene pieces and two large-size trapezoidal graphene pieces; the positive and negative poles of the direct current voltage source are connected to the upper graphene grating layer and the lower graphene grating layer respectively.

[0009] The small-size trapezoidal graphene piece and the large-size trapezoidal graphene piece each has an angle of 45° with the x-axis in the three-dimensional coordinate system; in one graphene grating layer, one small-size trapezoidal graphene piece and one large-size trapezoidal graphene piece form a group, and there are two groups, which are symmetrically distributed with the angle bisector of the x-axis and the y-axis as the axis of symmetry, and the large-size trapezoidal graphene piece is close to the angle bisector; and the trapezoidal waist of the small-size trapezoidal graphene piece and the large-size trapezoidal graphene piece coincides with the boundary of the adjustable polarization conversion unit.

[0010] Preferably, the adjustable polarization conversion unit is a square on the plane formed by the x-axis and the y-axis in the three-dimensional coordinate system; the long side of the rectangular metal piece is parallel to the x-axis, the short side is parallel to the y-axis, and the long side and the short side coincide with the boundary of the adjustable polarization conversion unit.

[0011] Preferably, the side length of the square is 16 μm; the long side of the rectangular metal piece is 16 μm, and the short side is 4 μm; the interval between the two rectangular metal pieces is 4 μm, symmetrically distributed with the x-axis as the axis of symmetry, and the thickness is 0.2 μm; the width of the small-size trapezoidal graphene piece and the large-size trapezoidal graphene piece is 3.8 μm, and the interval is 1.84 μm; the side length of the dielectric substrate layer is 16 μm, and the thickness is 40 μm; the side length of the silicon dioxide film isolation layer is 16 μm, and the thickness is 0.1 μm.

[0012] Preferably, the material of the rectangular metal piece is gold; the materials of the small-size trapezoidal graphene piece and the large-size trapezoidal graphene piece are both single-layer graphene, and the relaxation time is 0.2 ps; the material of the dielectric substrate layer is TOPAS, and the refractive index is 1.53; the material of the silicon dioxide film isolation layer is silicon dioxide, and the relative dielectric constant is 3.9.

[0013] Preferably, the adjustable polarization conversion units 1 are arranged in an M×N array, and M and N are both natural numbers greater than or equal to 1.

[0014] The graphene adjustable wideband terahertz polarization converter can be applied to terahertz wireless communication, imaging and sensing.

[0015] The graphene adjustable wideband terahertz polarization converter can be applied to the preparation of medical devices for biomedical diagnosis.

[0016] The graphene adjustable wideband terahertz polarization converter has the following advantages:

[0017] (1) The graphene tunable broadband terahertz polarization converter of the present invention can control the polarization of terahertz waves and convert the polarization angle of terahertz waves within a broadband range.

[0018] (2) The graphene grating of the present invention has a tunable polarization conversion function and is the core functional material of the present invention.

[0019] (3) The adjustable DC voltage source of the present invention has the function of adjusting the Fermi level of graphene.

[0020] (4) The graphene tunable broadband terahertz polarization converter of the present invention has the function of tunable polarization conversion angle, and the voltage can be adjusted to change the polarization angle as needed.

[0021] (5) The graphene tunable broadband terahertz polarization converter of the present invention adopts an artificial microstructure, with a simple unit structure, easy to process, and the materials are common and easy to process and manufacture.

[0022] (6) The graphene tunable broadband terahertz polarization converter of the present invention is composed of periodic units, which has a simple structure and does not require complex unit arrangement, making it easy to mass-produce.

[0023] (7) The graphene tunable broadband terahertz polarization converter of the present invention has wide application value in the fields of terahertz wireless communication, imaging and sensing, and biomedical diagnosis. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the top of a graphene-tunable broadband terahertz polarization converter.

[0025] Figure 2 This is a schematic diagram of the bottom of a graphene-tunable broadband terahertz polarization converter.

[0026] Figure 3 This is a top view of the metal grating layer;

[0027] Figure 4 A top view of the graphene grating layer;

[0028] Figure 5 A three-dimensional schematic diagram of a polarization conversion unit;

[0029] Figures 1-5 In the middle: 1. Adjustable polarization conversion unit; 2. Rectangular metal sheet; 3. Small-sized trapezoidal graphene sheet; 4. Large-sized trapezoidal graphene sheet; 5. Metal grating layer; 6. Dielectric substrate layer; 7. Upper graphene grating layer; 8. Lower graphene grating layer; 9. Silicon dioxide thin film isolation layer; 10. DC voltage source;

[0030] Figure 6The transmission coefficient curve is the S-parameter of graphene when the Fermi level is 0 eV.

[0031] Figure 7 The transmission coefficient curve is the S-parameter of graphene at a Fermi level of 1 eV.

[0032] Figure 8 The polarization conversion efficiency curve is shown when the Fermi level of graphene is 1 eV.

[0033] Figure 9 The electric field distribution diagrams for the tunable polarization conversion unit are as follows: when the Fermi level of graphene is 0 eV, (a) is 0.5 THz, (b) is 1.0 THz, and (c) is 1.5 THz; when the Fermi level of graphene is 1 eV, (d) is 0.5 THz, (e) is 1.0 THz, and (f) is 1.5 THz. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] A graphene-tunable broadband terahertz polarization converter, such as Figure 1 , Figure 2 As shown, it includes multiple adjustable polarization conversion units 1 arranged periodically in the same plane. The adjustable polarization conversion units 1 are arranged in a rectangular array on a plane perpendicular to the incident terahertz wave.

[0037] like Figure 1 , Figure 2 As shown, the adjustable polarization conversion unit 1 is arranged in an M×N array, where M and N are both natural numbers ≥1. Figure 1 The part outlined by the dashed line is the adjustable polarization conversion unit 1. The adjustable polarization conversion unit 1 is a square on the plane formed by the x-axis and y-axis in the three-dimensional coordinate system (the top view shows a square), with a side length of 16μm.

[0038] like Figure 5 As shown, in a three-dimensional spatial coordinate system, the adjustable polarization conversion unit 1 includes a metal grating layer 5, a dielectric substrate layer 6, an upper graphene grating layer 7, a silicon dioxide thin film isolation layer 9, a lower graphene grating layer 8, and a DC voltage source 10, which are stacked sequentially from top to bottom along the z-axis and parallel to the x-axis. The positive terminal of the DC voltage source 10 is connected to the upper graphene grating layer 7, and the negative terminal is connected to the lower graphene grating layer 8. The graphene Fermi level is controlled by adjusting the bias voltage.

[0039] like Figure 3As shown, the metal grating layer 5 is composed of two identical rectangular metal sheets 2 arranged at equal intervals. The rectangular metal sheets 2 coincide with the boundary of the adjustable polarization conversion unit 1, with a long side parallel to the x-axis of 16 μm and a wide side parallel to the y-axis of 4 μm. The two rectangular metal sheets 2 are spaced 4 μm apart, symmetrically distributed about the x-axis, and have a thickness of 0.2 μm. The material is gold.

[0040] like Figure 4 As shown, the upper graphene grating layer 7 and the lower graphene grating layer 8 have the same structure, both consisting of two small trapezoidal graphene sheets 3 and two large trapezoidal graphene sheets 4 symmetrically distributed at equal intervals. The small trapezoidal graphene sheets 3 and the large trapezoidal graphene sheets 4 each form a 45° angle with the x-axis in the three-dimensional coordinate system. In one graphene grating layer, one small trapezoidal graphene sheet 3 and one large trapezoidal graphene sheet 4 form a group, for a total of two groups. The two groups are symmetrically distributed about the angle bisectors of the x-axis and y-axis, with the two large trapezoidal graphene sheets 4 close to the angle bisectors. The waists of the trapezoids of the small trapezoidal graphene sheets 3 and the large trapezoidal graphene sheets 4 coincide with the boundary of the tunable polarization conversion unit 1. Both the small-sized trapezoidal graphene sheet 3 and the large-sized trapezoidal graphene sheet 4 have a width of 3.8 μm, a spacing of 1.84 μm, are made of single-layer graphene, and have a relaxation time of 0.2 ps.

[0041] The dielectric substrate layer 6 has a side length of 16μm, a thickness of 40μm, is made of TOPAS material, and has a refractive index of 1.53.

[0042] The silicon dioxide thin film isolation layer 9 has a side length of 16μm, a thickness of 0.1μm, is made of silicon dioxide, and has a relative permittivity of 3.9.

[0043] The electrical conductivity of graphene is influenced by its Fermi level, which can be controlled by a bias voltage applied between two graphene grating layers. When the Fermi level of graphene is 0 eV (i.e., when the DC voltage source outputs 0 V), the graphene grating layer is nearly transparent and does not perform polarization conversion. When the Fermi level of graphene is 1 eV (i.e., when the DC voltage source outputs 281 V), the conductivity of the graphene grating layer increases, enabling it to perform polarization conversion for terahertz waves.

[0044] The performance simulation results of the graphene tunable broadband terahertz polarization converter in this embodiment are as follows: Figures 6-9 As shown, the details are as follows:

[0045] like Figure 6The figure shows the co-polarization and cross-polarization transmission coefficient curves of the graphene tunable broadband terahertz polarization converter at the graphene Fermi level of 0 eV. The incident wave is a y-polarized plane wave. The solid line represents the co-polarization transmission coefficient, and the dashed line represents the cross-polarization transmission coefficient. As can be seen from the figure, the co-polarization transmission coefficient remains above 0.8, while the cross-polarization coefficient remains below 0.3. This indicates that the graphene grating layer in this embodiment maintains an unchanged polarization state of the incident wave at the graphene Fermi level of 0 eV, exhibiting good transparency.

[0046] like Figure 7 The figure shows the co-polarization and cross-polarization transmission coefficient curves of the graphene tunable broadband terahertz polarization converter when the graphene Fermi level is 1 eV. The incident wave is y-polarized. The solid line represents the co-polarization transmission coefficient, and the dashed line represents the cross-polarization transmission coefficient. As can be seen from the figure, within the frequency range of 0.428–1.707 THz, the transmission coefficients of the two curves are similar and relatively high, indicating that the y-polarized wave is converted into a linearly polarized wave with a polarization rotation angle of 45°. This demonstrates that when the graphene Fermi level is 1 eV, the graphene tunable broadband terahertz polarization converter of this embodiment can achieve polarization conversion.

[0047] like Figure 8 The figure shows a simulation of the polarization conversion efficiency of the graphene tunable broadband terahertz polarization converter with a graphene Fermi level of 1 eV. As can be seen from the figure, in the operating frequency band of 0.428–1.707 THz, the polarization conversion efficiency remains above 80% when converting a co-polarized incident wave into a transmitted wave with a polarization rotation angle of 45°, with a relative bandwidth of 120%. These results demonstrate that the graphene tunable broadband terahertz polarization converter of this embodiment exhibits high polarization conversion efficiency at a graphene Fermi level of 1 eV.

[0048] like Figure 9 The diagram shows the electric field distribution of a graphene-tunable broadband terahertz polarization converter, with all incident waves being γ-polarized waves. Figure 9 In the middle (a), the electric field distribution of the transmitted wave at frequency f = 0.5 THz is shown when the Fermi level of graphene is 0 eV. Figure 9 (b) shows the electric field distribution of the transmitted wave at frequency f = 1.0 THz when the Fermi level of graphene is 0 eV. Figure 9 Image (c) shows the electric field distribution of the transmitted wave at frequency f = 1.5 THz when the Fermi level of graphene is 0 eV. Figure 9 The middle (d) diagram shows the electric field distribution of the transmitted wave at a frequency of f = 0.5 THz when the Fermi level of graphene is 1 eV. Figure 9 Image (e) shows the electric field distribution of the transmitted wave at frequency f = 1.0 THz when the Fermi level of graphene is 1 eV. Figure 9 Figure (f) shows the electric field distribution of the transmitted wave at frequency f = 1.5 THz when the Fermi level of graphene is 1 eV. Figure 9As shown in (a), (b), and (c), when the Fermi level of graphene is 0 eV, the transmitted wave is still a y-polarized wave when a y-polarized wave is incident, exhibiting good transparency. From... ​ As shown in (d), (e), and (f), when the Fermi level of graphene is 1 eV, the incident y-polarized wave is converted into a linearly polarized wave with an angle of 45° to the y-axis. Therefore, the tuning function of the graphene tunable broadband terahertz polarization converter can be realized by changing the Fermi level of graphene.

[0049] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A graphene-tunable broadband terahertz polarization converter, characterized in that, It includes multiple adjustable polarization conversion units (1) arranged in a rectangular array in the same plane; according to the three-dimensional coordinate system, the adjustable polarization conversion unit (1) includes a metal grating layer (5), a dielectric substrate layer (6), an upper graphene grating layer (7), a silicon dioxide thin film isolation layer (9), a lower graphene grating layer (8), and a DC voltage source (10) that are stacked sequentially from top to bottom along the z-axis and parallel to the x-axis. The metal grating layer (5) is composed of two identical rectangular metal sheets (2) arranged at equal intervals; the upper graphene grating layer (7) and the lower graphene grating layer (8) have the same structure, both composed of two small trapezoidal graphene sheets (3) and two large trapezoidal graphene sheets (4) symmetrically arranged; the positive and negative terminals of the DC voltage source (10) are respectively connected to the upper graphene grating layer (7) and the lower graphene grating layer (8). The small-sized trapezoidal graphene sheet (3) and the large-sized trapezoidal graphene sheet (4) both have an angle of 45° with the x-axis in the three-dimensional coordinate system. In one graphene grating layer, one small-sized trapezoidal graphene sheet (3) and one large-sized trapezoidal graphene sheet (4) form a group, with a total of two groups. The two groups are symmetrically distributed with the angle bisectors of the x-axis and y-axis as the axis of symmetry, and the large-sized trapezoidal graphene sheet (4) is close to the angle bisector. The trapezoidal waists of the small-sized trapezoidal graphene sheet (3) and the large-sized trapezoidal graphene sheet (4) coincide with the boundary of the tunable polarization conversion unit (1). The adjustable polarization conversion unit (1) is a square on the plane formed by the x-axis and y-axis in the three-dimensional coordinate system; the long side of the rectangular metal sheet (2) is parallel to the x-axis, the wide side is parallel to the y-axis, and coincides with the boundary of the adjustable polarization conversion unit (1); The square has a side length of 16 μm; the rectangular metal sheet (2) has a long side of 16 μm and a wide side of 4 μm; the two rectangular metal sheets (2) are spaced 4 μm apart, symmetrically distributed with the x-axis as the axis of symmetry, and have a thickness of 0.2 μm; the small-sized trapezoidal graphene sheet (3) and the large-sized trapezoidal graphene sheet (4) are both 3.8 μm wide and spaced 1.84 μm apart; the dielectric substrate layer (6) has a side length of 16 μm and a thickness of 40 μm; the silicon dioxide thin film isolation layer (9) has a side length of 16 μm and a thickness of 0.1 μm; The rectangular metal sheet (2) is made of gold; the small-sized trapezoidal graphene sheet (3) and the large-sized trapezoidal graphene sheet (4) are both made of single-layer graphene with a relaxation time of 0.2 ps; the dielectric substrate layer (6) is made of TOPAS with a refractive index of 1.53; the silicon dioxide thin film isolation layer (9) is made of silicon dioxide with a relative permittivity of 3.

9. The adjustable polarization conversion unit (1) is arranged in an M×N column, where M and N are both natural numbers ≥1.

2. The application of the graphene tunable broadband terahertz polarization converter as described in claim 1 in terahertz wireless communication, imaging and sensing.

3. The application of the graphene tunable broadband terahertz polarization converter according to claim 1 in the preparation of medical devices for biomedical diagnosis.

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