A terahertz bandwidth tunable filter

Abstract

This invention relates to a tunable bandwidth terahertz filter. The tunable bandwidth terahertz filter comprises multiple periodically arranged unit structures. The structure of each filter unit is as follows: the lower plane of a first composite layer (1) is in close contact with the upper plane of a first dielectric layer (2), and the lower plane of the first dielectric layer (2) is in close contact with the upper plane of a square metal ring (3); the upper plane of a second dielectric layer (4) is in close contact with the lower plane of the square metal ring (3), and the upper plane of a second composite layer (5) is in close contact with the lower plane of the second dielectric layer (4). The resulting broadband filter can achieve a reduction in relative bandwidth from 110.4% to 99.4%. This invention has a simple structure and features high transmittance, tunable bandwidth, and polarization insensitivity.

Description

Technical Field

[0001] This invention belongs to the field of terahertz metamaterial devices, specifically relating to a terahertz bandwidth tunable filter, which can be used for the development of terahertz filters. Background Technology

[0002] Terahertz waves, also known as terahertz radiation or THz radiation, refer to electromagnetic waves with frequencies between 0.1 and 10 terahertz (THz) and wavelengths ranging from approximately 30 to 300 micrometers. Located between microwaves and infrared radiation in the electromagnetic spectrum, this frequency band was previously considered the "terahertz gap" because traditional technologies and materials struggled to effectively generate, detect, and manipulate these waves. Terahertz wave generation primarily relies on femtosecond laser pulses or synchrotron radiation, while detection typically depends on pyroelectric detectors, photoconductive detectors, etc. Terahertz waves exhibit high penetrability to certain non-polar materials, have low photon energy, do not induce ionizing radiation, are relatively safe for the human body, and fall between microwaves and infrared radiation. Therefore, they have immense application potential in non-invasive security inspections. With advancements in materials science, optoelectronics, and micro / nano manufacturing technologies, research and applications of terahertz waves have developed rapidly. Governments and research institutions worldwide are increasing their investment in terahertz technology research, aiming for breakthroughs in national security, biomedicine, and information technology. Terahertz waves are considered to have great potential for future technological development due to their unique physical properties.

[0003] Metamaterials are a new type of material whose artificially designed microstructures possess physical properties that surpass those of traditional natural materials on a macroscopic scale. By designing artificial structures at the subwavelength scale (i.e., smaller than the wavelength of light), metamaterials can control the propagation of electromagnetic waves in specific ways. These artificial structures are typically composed of basic materials such as metals, insulators, or semiconductors, and through precise geometric arrangement and sizing, they can achieve properties that surpass those of natural materials, such as negative refractive index, perfect lens effect, and cloaking capabilities. Metamaterials have wide applications in optics, including optical imaging, photonic crystals, and optical communication. They not only have profound significance in theoretical physics but also enormous potential in practical applications, greatly promoting the development of related technologies and science.

[0004] Traditional terahertz metamaterial filters based on metal patches have limited practical applications due to their fixed operating frequency. With ongoing research, many single-band, multi-band, and wideband tunable terahertz metamaterial filters have been designed and fabricated, but some problems still need to be solved. Therefore, many researchers aim to study terahertz metamaterial filters with good tuning performance. That is, under the premise of good filtering performance, research is being conducted on terahertz metamaterial filters with advantages such as wide tuning range, wide tuning frequency, simple tuning methods, and high tuning accuracy.

[0005] To address the technical problems existing in the prior art, the primary objective of this invention is to provide a terahertz bandwidth tunable filter based on vanadium dioxide. This filter has a simple structure and a wide filtering bandwidth. Furthermore, the transmittance of this filter can be tuned by adjusting the conductivity of vanadium dioxide. To achieve the above objective, this invention proposes a terahertz bandwidth tunable filter based on vanadium dioxide, providing the following solution:

[0006] It should be noted that since the terahertz metamaterial filter is composed of unit structures arranged periodically, the size of which can be arranged according to one's own needs, the following steps only introduce the design of the unit structures.

[0007] like Figure 2 As shown, the structure of the terahertz broadband filter unit consists of a first composite layer (1), a first dielectric layer (2), a square metal ring (3), a second dielectric layer (4), and a second composite layer (5); the lower plane of the first composite layer (1) is in close contact with the upper plane of the first dielectric layer (2), and the lower plane of the first dielectric layer (2) is in close contact with the upper plane of the square metal ring (3); the upper plane of the second dielectric layer (4) is in close contact with the lower plane of the square metal ring (3), and the upper plane of the second composite layer (5) is in close contact with the lower plane of the second dielectric layer (4).

[0008] The square metal ring (3) is located at the middle position in the height direction of the terahertz filter unit; the first composite layer (1) and the second composite layer (5) are symmetrically arranged; the first dielectric layer (2) and the second dielectric layer (4) are symmetrically arranged; the centroids of the first composite layer (1), the first dielectric layer (2), the square metal ring (3), the second dielectric layer (4) and the second composite layer (5) coincide with the center line of the terahertz filter unit.

[0009] like Figure 3As shown, the first composite layer (1) has four identical VO2 square patches with a side length of L1 = 7.5µm as its core. The exterior of each VO2 square patch is tightly connected to a gold resonant ring with a width of W1 = 1µm and a length of L3 = 7µm. The distance between the gold resonant rings is L2 = 20µm. The overall structure forms a centrally symmetrical structure. The second composite layer (5) is the same as the first composite layer (1).

[0010] like Figure 4 As shown, the square metal ring (3) has a square ring structure, and the ring width W = 0.5.

[0011] Both the first dielectric layer (2) and the second dielectric layer (4) use polyimide as the filling medium, and the dielectric constants of the first dielectric layer (2) and the second dielectric layer (4) are 3.5.

[0012] The metal ring is made of gold.

[0013] The dielectric constant of the vanadium dioxide In the THz band, the Drude model is used to represent:

[0014]

[0015] =12 is the relative permittivity at infinite frequency;

[0016] γ represents the collision frequency, γ = 5.75 × 10⁻⁶ 13 rad / s;

[0017] The plasma frequency. and The relationship is:

[0018]

[0019] In the formula: Indicates temperature-dependent conductivity. =3×10 5 S / m;

[0020] This represents the electrical conductivity of vanadium dioxide in its insulating state. =200S / m; in the metallic state =200000S / m;

[0021] This indicates the plasma frequency, which depends on the electrical conductivity. =1.4×10 15 rad / s.

[0022] The square metal ring (3) is made of the same material as the first composite layer (1) and the second composite layer (5); the thickness of the square metal ring (3) is the same as the thickness h2 of the first composite layer (1) and the second composite layer (5). h2 = 0.5µm.

[0023] The four sides of the first dielectric layer (2), the square metal ring (3), and the second dielectric layer (4) of the terahertz filter have a side length of p = 22µm.

[0024] The first dielectric layer (2) and the second dielectric layer (4) have the same thickness h1. h1 = 3µm.

[0025] In the simulation, the vanadium dioxide was set to an insulating state and a metallic state, respectively, with the temperature in the insulating state ≤300K and the temperature in the metallic state ≥340K;

[0026] The beneficial effects of this invention are as follows:

[0027] (1) The terahertz bandwidth tunable filter based on vanadium dioxide proposed in this invention can adjust the filtering performance without changing the structural parameters by utilizing the phase transition characteristics of vanadium dioxide. Specifically, when VO2 is in an insulating state, its conductivity is 2×102 S / m (T=300K). The designed metamaterial filter exhibits a wide passband in the range of 2.494~6.077THz, with a transmission coefficient exceeding 90% within this range, and a relative bandwidth as high as 110.4% at the center frequency f0=4.267THz. Two transmission peaks exist at f1=3.155THz and f2=5.407THz, with a maximum transmission coefficient of 97%. However, when an external excitation is applied, as the conductivity of VO2 increases, VO2 changes from an insulating state to a fully metallic state. When its conductivity is 2×10⁵ S / m (T=350K), i.e. in the metallic state, the wide passband of the designed metamaterial filter switches to 1.549~4.613THz, with a transmission coefficient exceeding 90% in this range. The relative bandwidth at the center frequency f0=3.081THz is 99.4%, and there are two transmission peaks at f1=2.188THz and f2=3.897THz, with a maximum transmission coefficient of 93.15%.

[0028] (2) The terahertz bandwidth tunable filter based on vanadium dioxide proposed in this invention exhibits good polarization insensitivity to polarization angle.

[0029] (3) The terahertz bandwidth tunable filter based on vanadium dioxide proposed in this invention shows that the thickness of the dielectric layer, the length of the gold resonant ring and the ring spacing can be precisely controlled to achieve the center frequency and bandwidth of the passband. The width of the gold resonant ring has little effect on the transmission characteristics, giving the device good process tolerance. Attached Figure Description

[0030] To make the content of this invention easier to understand, specific embodiments of the invention are described below in conjunction with...

[0031] The accompanying drawings provide a further detailed description of the invention, in which:

[0032] Figure 1 This is a schematic diagram of a 3×3 unit array structure of a terahertz bandwidth tunable filter based on vanadium dioxide, as described in this invention.

[0033] Figure 2 This is a schematic diagram of the structure of a single unit of a vanadium dioxide-based terahertz bandwidth tunable filter according to the present invention.

[0034] Figure 3 for Figure 1 A top view of the first composite layer (1) in a vanadium dioxide-based terahertz bandwidth tunable filter unit;

[0035] Figure 4 for Figure 1 A top view of the square metal ring (3) in a vanadium dioxide-based terahertz bandwidth tunable filter unit;

[0036] Figure 5 for Figure 1 The transmittance simulation results of a terahertz bandwidth tunable filter based on vanadium dioxide as a function of the conductivity of vanadium dioxide are presented.

[0037] Figure 6 for Figure 1 The simulation results of the transmittance of a terahertz bandwidth tunable filter based on vanadium dioxide as the polarization angle varies with the vanadium dioxide in the insulating state.

[0038] Figure 7 for Figure 1 Simulation results of the transmittance of a terahertz bandwidth tunable filter based on vanadium dioxide as the polarization angle varies with the polarization angle when vanadium dioxide is in the metallic state. Detailed Implementation

[0039] The technical methods of this invention will be fully and clearly described below with reference to the accompanying drawings, enabling those skilled in the art to easily and smoothly understand the advantages and details of this invention. Obviously, the examples described below are merely specific examples of this invention, and this invention can be implemented through different examples. Details such as dimensions and positions described in this invention can also be slightly modified for different examples without departing from the spirit of this invention. Therefore, other examples obtained without inventive modifications also fall within the scope of this invention.

[0040] like Figure 2 As shown, the structure of the terahertz broadband filter unit consists of a first composite layer (1), a first dielectric layer (2), a square metal ring (3), a second dielectric layer (4), and a second composite layer (5); the lower plane of the first composite layer (1) is in close contact with the upper plane of the first dielectric layer (2), and the lower plane of the first dielectric layer (2) is in close contact with the upper plane of the square metal ring (3); the upper plane of the second dielectric layer (4) is in close contact with the lower plane of the square metal ring (3), and the upper plane of the second composite layer (5) is in close contact with the lower plane of the second dielectric layer (4).

[0041] The square metal ring (3) is located at the middle position in the height direction of the terahertz filter unit; the first composite layer (1) and the second composite layer (5) are symmetrically arranged; the first dielectric layer (2) and the second dielectric layer (4) are symmetrically arranged; the centroids of the first composite layer (1), the first dielectric layer (2), the square metal ring (3), the second dielectric layer (4) and the second composite layer (5) coincide with the center line of the terahertz filter unit.

[0042] like Figure 3 As shown, the first composite layer (1) has four identical VO2 square patches with a side length of L1 = 7.5µm as its core. The exterior of each VO2 square patch is tightly connected to a gold resonant ring with a width of W1 = 1µm and a length of L3 = 7µm. The distance between the gold resonant rings is L2 = 20µm. The overall structure forms a centrally symmetrical structure. The second composite layer (5) is the same as the first composite layer (1).

[0043] like Figure 4 As shown, the square metal ring (3) has a square ring structure, and the ring width W2 of the square metal ring (3) is 0.5.

[0044] Both the first dielectric layer (2) and the second dielectric layer (4) use polyimide as the filling medium, and the dielectric constants of the first dielectric layer (2) and the second dielectric layer (4) are 3.5.

[0045] The metal ring is made of gold.

[0046] The dielectric constant of the vanadium dioxide In the THz band, the Drude model is used to represent:

[0047]

[0048] =12 is the relative permittivity at infinite frequency;

[0049] γ represents the collision frequency, γ = 5.75 × 10⁻⁶ 13 rad / s;

[0050] The plasma frequency. and The relationship is:

[0051]

[0052] In the formula: Indicates temperature-dependent conductivity. =3×10 5 S / m;

[0053] This represents the electrical conductivity of vanadium dioxide in its insulating state. =200S / m; in the metallic state =200000S / m;

[0054] This indicates the plasma frequency, which depends on the electrical conductivity. =1.4×10 15 rad / s.

[0055] The square metal ring (3) is made of the same material as the first composite layer (1) and the second composite layer (5); the thickness of the square metal ring (3) is the same as the thickness h2 of the first composite layer (1) and the second composite layer (5). h2 = 0.5µm.

[0056] The four sides of the first dielectric layer (2), the square metal ring (3), and the second dielectric layer (4) of the terahertz filter have a side length of p = 20µm.

[0057] The first dielectric layer (2) and the second dielectric layer (4) have the same thickness h1. h1 = 3µm.

[0058] In the simulation, the vanadium dioxide was set to an insulating state and a metallic state, respectively, with the temperature in the insulating state ≤300K and the temperature in the metallic state ≥340K;

[0059] When VO2 is in its insulating state, its conductivity is 2 × 10² S / m (T = 300 K). The designed metamaterial filter exhibits a wide passband in the range of 2.494–6.077 THz, with a transmission coefficient exceeding 90% within this range. At the center frequency f0 = 4.267 THz, the relative bandwidth reaches 110.4%, and the maximum transmission coefficient is 97%. However, when external excitation is applied, as the conductivity of VO2 increases, it transforms from an insulating state to a fully metallic state. When its conductivity reaches 2 × 10⁵ S / m (T = 350 K), i.e., in the metallic state, the wide passband of the designed metamaterial filter switches to the range of 1.549–4.613 THz, with a transmission coefficient exceeding 90% within this range. At the center frequency f0 = 3.081 THz, the relative bandwidth is 99.4%, and the maximum transmission coefficient is 93.15%.

[0060] The beneficial effects of this invention are as follows:

[0061] (1) The terahertz bandwidth tunable filter based on vanadium dioxide proposed in this invention can adjust the filtering performance without changing the structural parameters by utilizing the phase transition characteristics of vanadium dioxide. Figure 5 As can be seen, when VO2 is in an insulating state, its conductivity is 2 × 10² S / m (T = 300 K). The designed metamaterial filter exhibits a wide passband in the range of 2.494–6.077 THz, with a transmission coefficient exceeding 90% within this range. At the center frequency f0 = 4.267 THz, the relative bandwidth reaches 110.4%, and the maximum transmission coefficient is 97%. However, when external excitation is applied, as the conductivity of VO2 increases, VO2 transitions from an insulating state to a fully metallic state. When its conductivity reaches 2 × 10⁵ S / m (T = 350 K), i.e., in the metallic state, the wide passband of the designed metamaterial filter switches to the range of 1.549–4.613 THz, with a transmission coefficient exceeding 90% within this range. At the center frequency f0 = 3.081 THz, the relative bandwidth is 99.4%, and the maximum transmission coefficient is 93.15%.

[0062] (2) The terahertz bandwidth tunable filter based on vanadium dioxide proposed in this invention exhibits good polarization insensitivity to polarization angles. Figure 6 and Figure 7 The transmittance simulation results of the terahertz ultrawideband filter with varying polarization angles were analyzed when vanadium dioxide was in both insulating and metallic states. Figure 6 and Figure 7 It can be seen that the transmittance of the filter hardly changes with the angle.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to specific embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A terahertz filter with tunable bandwidth, characterized in that, The structure of the terahertz broadband filter unit is as follows: the lower plane of the first composite layer (1) is in close contact with the upper plane of the first dielectric layer (2), the lower plane of the first dielectric layer (2) is in close contact with the upper plane of the square metal ring (3); the upper plane of the second dielectric layer (4) is in close contact with the lower plane of the square metal ring (3), and the upper plane of the second composite layer (5) is in close contact with the lower plane of the second dielectric layer (4). The first composite layer (1) and the second composite layer (5) are symmetrically arranged, and the first dielectric layer (2) and the second dielectric layer (4) are symmetrically arranged. The centroids of the first composite layer (1), the first dielectric layer (2), the square metal ring (3), the second dielectric layer (4), and the second composite layer (5) coincide with the center line of the terahertz ultra-wideband filter unit. The four sides of the first dielectric layer (2), the square metal ring (3), and the second dielectric layer (4) are flush, and the side lengths p×p of the four sides are equal.

2. The tunable terahertz broadband filter according to claim 1, characterized in that, The four sides of the first dielectric layer (2), the square metal ring (3), and the second dielectric layer (4) of the terahertz filter have a side length P = 22µm.

3. A tunable terahertz broadband filter according to claim 1, characterized in that, The first composite layer (1) has four identical VO2 square patches with a side length of L1=7.5µm as its core. The exterior of each VO2 square patch is tightly connected to a gold resonant ring with a width of W1=1µm and a length of L3=7µm. The distance between the gold resonant rings is L2=20µm. The overall structure forms a centrally symmetrical structure. The second composite layer (5) is the same as the first composite layer (1).

4. A tunable terahertz broadband filter according to claim 1, characterized in that, The first dielectric layer (2) and the second dielectric layer (4) are made of polyimide with a dielectric constant of 3.

5.

5. A tunable terahertz broadband filter according to claim 1, characterized in that, The first dielectric layer (2) and the second dielectric layer (4) have the same thickness t1 and the thickness h1 = 3µm.

6. A tunable terahertz broadband filter according to claim 1, characterized in that, The first composite layer (1) and the second composite layer (5) have the same thickness t2, and the thickness h2 = 0.5µm.

7. A tunable terahertz broadband filter according to claim 1, characterized in that, The square metal ring (3) is located at the middle position in the height direction of the terahertz filter unit; the square metal ring (3) is a square ring structure, and the ring width W2 of the square metal ring (3) is 0.

5.

8. A tunable terahertz broadband filter according to claim 1, characterized in that, The metal ring is made of gold.

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