Broadband-adjustable terahertz wave absorber based on interdigital structure graphene

Abstract

The invention provides a graphene broadband adjustable terahertz wave absorber based on an interdigital structure. The wave absorber is of a three-layer structure which is composed of a metal layer, a polyimide dielectric layer and an interdigital structure graphene layer from bottom to top. An interdigital structure with the optimal size is selected through optimized scanning, a metal electrode is used for uniformly regulating and controlling the Fermi level and the relaxation time of graphene, and dynamic regulation and control in a broadband (2.2-5.1 THz) can be realized by regulating the Fermi level (0.6-1 eV) and the relaxation time (0.1-0.3 ps). In addition, the invention also has the advantages of easiness in preparation, capability of being combined with an integrated circuit process and the like. Therefore, in the terahertz field, such as imaging, stealth and switch operation equipment, the device has a wide application prospect.

Description

Technical Field

[0001] The invention relates to a broadband adjustable terahertz absorber based on interdigital structure graphene, and belongs to the field of micro-nano optoelectronic integration. Background Art

[0002] Metamaterials are artificial engineering materials with subwavelength structures. They have the characteristics of negative refractive index and negative dielectric constant, which have attracted special attention. The plasma frequency of graphene materials and the band gap of nanoribbons are both in the terahertz (THz) range. Graphene metasurfaces can resonate with electromagnetic waves to excite surface plasmons, and the surface conductivity of graphene can be regulated by external voltage, which makes graphene a new way for reconfigurable metasurfaces and metamaterials. People have successfully applied it to various optoelectronic devices, such as absorbers, polarizers, sensors and waveguides.

[0003] The present invention provides an absorber with an asymmetric graphene interdigital structure. The structure utilizes the localized surface plasmon polaritons of graphene in the terahertz band and exhibits strong localized plasmon resonance in the absorption spectrum. By adjusting the arm length of the interdigital structure, the absorption bandwidth can be expanded and compressed. At the same time, the structure can be combined with the integrated circuit process. The flexible selection of the working bandwidth can be achieved through different interdigital electrode masks. By adjusting the Fermi level and relaxation time of graphene, the absorption peak can be effectively adjusted. Therefore, the structure proposed in this article has good dynamic adjustable energy capability and provides a new strategy for the design of absorbers. Summary of the invention

[0004] The invention relates to a broadband adjustable terahertz absorber based on interdigital graphene structure, which has a simple structure and is easy to prepare.

[0005] The present invention is achieved through the following technical solutions: based on the interdigital structure graphene broadband adjustable terahertz absorber, such as Figure 1 As shown in (a), the absorber is composed of a metal electrode layer, a dielectric layer composed of polyimide (PI), and a graphene layer with an interdigitated structure from bottom to top.

[0006] The unit structure of interdigitated graphene is as follows Figure 1 As shown in (b), the arm lengths are L1 and L2, the arm width is W, the unit structure period is P, and the number of interdigital structures is selected through FDTD parameter optimization.

[0007] The plane light source is incident vertically from the z direction, where the x and y directions are periodic boundary conditions and the z direction is set as a perfectly matched layer (PML).

[0008] Compared with the prior art, the present invention has the following advantages:

[0009] Research has found that the structure designed in the present invention can achieve multi-band adjustable absorption compared with other absorber structures, and the finger structure is widely used in integrated circuits. The design can be combined with existing processes and is easy to prepare. Specifically, changing the number and length of the fingers can achieve bandwidth expansion and compression, and the Fermi level of graphene can be changed by applying an external voltage to achieve adjustability of the absorption peak, providing new ideas for applications in military and medical fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 (a) is a schematic diagram of the structure of the present invention, wherein 1 is a metal electrode layer, 2 is a dielectric layer composed of polyimide (PI), and 3 is a graphene layer.

[0011] Figure 1 (b) is the graphene unit structure of the present invention, wherein L1 and L2 are the structure arm lengths, W is the structure arm width, and P is the unit structure period.

[0012] Figure 2 This is a graph of absorption and reflection spectra of the present invention when the graphene Fermi level is fixed at 1 eV and the relaxation time is 0.1 ps.

[0013] Figure 3 (a) is the absorption spectrum curve of the graphene supersurface at different Fermi levels (0.6-1 eV) when the relaxation time is fixed at 0.1 ps in the present invention.

[0014] Figure 3 (b) is the absorption spectrum curve of the graphene supersurface at different relaxation times (0.1 to 0.3 ps) when the Fermi level is fixed at 1 eV in the present invention.

[0015] Figure 4 (a) is the absorption curve of the present invention when the arm length L1 is fixed and the number of interdigits is changed.

[0016] Figure 4 (b) is the absorption spectrum curve of the present invention when the number of fingers is fixed to 4 and the arm length L1 is changed. DETAILED DESCRIPTION

[0017] In order to better understand the present invention, the present invention is further explained below in conjunction with embodiments and drawings. The following embodiments are only used to illustrate the present invention but are not intended to limit it.

[0018] Figure 1 (a) is a schematic diagram of the unit structure of the present invention, where the absorber is composed of a metal electrode layer, a dielectric layer composed of polyimide (PI), and a graphene layer with an interdigitated structure from bottom to top. The unit structure shown is a polyimide layer with a thickness of H2 of 10 μm deposited on gold with a thickness of H1 of 0.2 μm.

[0019] Figure 1 (b) is a schematic diagram of the unit structure of the graphene layer of the present invention, where the period P of the unit structure is 10 μm, L1 and L2 are the lengths of the two arms, and W is the arm width.

[0020] The size parameters of the unit structure of the graphene metasurface are selected through FDTD optimization. The method is: fix the graphene Fermi level to 1eV, the relaxation time to 0.1ps, the incident light to 1~6THz, analyze the arm length L1 of the graphene and the number of interdigital structures, and analyze the absorption rate and absorption bandwidth of different unit size structures. The unit structure finally selected can produce perfect absorption when f1 is 2.508THz and f2 is 4.033THz, and the absorption rate in the frequency range of the absorption bandwidth Δf=2.468THz is higher than 90%, such as Figure 2 shown.

[0021] When the relaxation time is 0.1ps, as the Fermi level changes (0.6-1eV), the graphene metasurface can produce different resonances and different absorption bandwidths. As the Fermi level decreases, the absorption bandwidth gradually decreases and a red shift occurs, such as Figure 3 (a) shown.

[0022] When the Fermi level is 1eV, as the relaxation time changes (0.1-0.3ps), the graphene metasurface can produce different resonances and different absorption bandwidths. As the relaxation time increases, the absorption rate gradually decreases and a blue shift occurs, such as Figure 3 (b) as shown.

[0023] Figure 4 (a) is the absorption spectrum of changing the number of fingers in the structure when the arm length L1 of the interdigital structure is fixed at 6.5μm. The horizontal axis is the incident light frequency and the vertical axis is the absorption rate. It can be seen from the figure that when the number of interdigits gradually decreases, the absorption bandwidth also decreases, and a high absorption rate is maintained, which proves that the proposed structure can adapt to different working ranges by adjusting the structure.

[0024] Figure 4 (b) is the absorption spectrum of the structure with a fixed number of interdigits of 4 and a changed interdigit arm length L1. The horizontal axis is the incident light frequency and the vertical axis is the absorptivity. As can be seen from the figure, when the interdigit arm length L1 gradually decreases, the absorption bandwidth also decreases, and the absorptivity also decreases. Therefore, it is proved that the proposed structure can enhance the localized plasma resonance by adjusting the structure to meet the requirements of high absorption and broadband.

[0025] It should be noted that although the embodiments of the present invention described above are illustrative, they are not intended to limit the present invention, and therefore the present invention is not limited to the above specific embodiments. Without departing from the principles of the present invention, any other embodiments obtained by those skilled in the art under the guidance of the present invention are deemed to be within the protection of the present invention.

Claims

1. A broadband tunable terahertz absorber based on interdigitated graphene, as shown in FIG1(a), characterized in that: The absorber unit is composed of a three-layer structure, which comprises, from bottom to top, a metal layer (1), a dielectric layer (2) composed of polyimide, and a graphene layer (3) with an interdigitated structure.

2. A broadband tunable terahertz absorber based on interdigitated graphene structure according to claim 1, as shown in FIG1(b), characterized in that: The period of the absorber unit is P, which is fixed at 10μm, the arm length L1 of the forked structure is 6.5μm, the arm length L2 is 6.5μm, and the arm width W is 0.5μm; the unit structure size parameters are selected through FDTD optimization, the method is: fix the graphene Fermi level to 1.0eV, the relaxation time τ to 0.1ps, optimize the graphene forked structure parameters (L1) and the number of forked fingers, analyze the absorption rate and absorption bandwidth of unit structures of different sizes, and select the optimal solution. The final selected unit structure still maintains a high absorption rate of more than 90% in the Δf=2.468THz band, as shown in Figure 2.

3. The broadband tunable terahertz absorber based on interdigitated graphene structure according to claim 1, characterized in that: The dielectric layer (2) is made of polyimide material with a relative dielectric constant of 3.5, and the dielectric layer thickness H2 is fixed at 12 μm.

4. The broadband tunable terahertz absorber based on interdigitated graphene structure according to claim 1, characterized in that: The substrate (3) is made of gold material, and the plasma frequency of the gold material is 1.37×10 16 rad / s, the collision frequency is 4.08×10 13 rad / s, and the thickness H1 is fixed at 0.2μm.

5. The broadband tunable terahertz absorber based on interdigitated graphene structure according to claim 1, characterized in that: The metal electrode layer is used to uniformly control the Fermi level and relaxation time of graphene. By adjusting the Fermi level (0.6-1 eV) and relaxation time (0.1-0.3 ps) of graphene, the absorption bandwidth can be dynamically controlled from 2.2 to 5.1 THz, as shown in FIG3 .

6. The broadband tunable terahertz absorber based on interdigitated graphene structure according to claim 1, characterized in that: By fixing the graphene Fermi level at 1 eV and the relaxation time τ at 0.1 ps, and adjusting the length L1 and the number of fingers of the interdigital structure, the absorber can dynamically adjust the absorption bandwidth while maintaining a high absorption rate, as shown in FIG4 .

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