Vanadium dioxide-based dynamic tunable chiral terahertz broadband absorber and preparation method thereof

Abstract

The invention discloses a dynamic tunable chiral terahertz broadband absorber based on vanadium dioxide, the absorber is formed by periodically arranging M * N absorption units of a multilayer structure in an array, the absorption units are in M * N two-dimensional distribution, and both M and N are positive integers; the absorption unit comprises a metal substrate, a dielectric layer and a resonance layer which are sequentially arranged from bottom to top; the metal substrate and the dielectric layer are rectangular; the resonance layer comprises a J-shaped metal patch, and an inverted-T-shaped vanadium dioxide patch is arranged at one end of the J-shaped metal patch. The terahertz chiral absorber can have a circular dichroism (CD) value larger than 0.8 within the range of 5.36-7.69 THz, the mirror image enantiomer of the terahertz chiral absorber can also achieve a CD spectrum opposite to the mirror image enantiomer, and the terahertz chiral absorber has the advantages of being high in CD, dynamically tunable and simple in structure. In addition, the invention also discloses a preparation method of the dynamic tunable chiral terahertz broadband absorber based on vanadium dioxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz wave absorbers, and specifically relates to the structural design of a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide, and also relates to a preparation method of the dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. Background Art

[0002] Terahertz (THz) waves generally refer to electromagnetic waves with frequencies between 0.1 and 10 THz. Due to their low energy, strong penetration, and unique frequency and wavelength, the application of THz waves and related technologies has become a research hotspot in various fields. As fundamental functional devices for THz applications, THz absorbers are widely used in detectors, spectrum imaging, stealth, and other fields.

[0003] Metamaterials are a class of artificially designed materials whose unit structures are much smaller than the operating wavelength, and whose structural units are arranged in a periodic pattern. By appropriately designing the geometry and parameters of the unit structures, electromagnetic properties not found in natural materials can be achieved, such as negative refractive index and the inverse Doppler effect. Notably, compared to natural materials, the unique electromagnetic properties of metamaterials depend on their structural composition rather than the properties of the material itself. Similarly, by analogy with the compositional laws of natural materials, the unit structures of metamaterials can be viewed as artificial atoms or molecules. By adjusting the shape and size of the unit structures, the interaction between the structure and the incident electromagnetic wave can be manipulated to achieve extraordinary electromagnetic functions, such as efficient absorption, broadband, polarization conversion, and optical imaging that breaks the diffraction limit.

[0004] Chirality is a ubiquitous phenomenon, a geometric property of an object that prevents it from being reconstructed into its mirror image through any manipulation, such as translation or rotation. Optical chirality arises from the differences in optical responses (i.e., absorption, transmission, and reflection) to different types of circularly polarized waves (CPLs), a phenomenon known as circular dichroism (CD). Due to the relative scarcity of chiral materials in nature, research on the interaction between CPLs and matter has been limited. With the continuous advancement of micro- and nanofabrication technologies and the integration of interdisciplinary research, research has expanded beyond the response to linearly polarized waves. In recent years, the differential absorption characteristics of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) waves, as well as the chirality-dependent electromagnetically induced transparency (EIT) effect, have also garnered attention. Chiral absorption manifests as differential responses to left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) waves. When a chiral metamaterial's surface is incident on a LCP or RCP electromagnetic wave, only one type of wave is efficiently absorbed.

[0005] The geometric structure of the chiral absorber is used to selectively absorb circularly polarized electromagnetic waves of different hand directions. By designing an absorber unit with a chiral structure, efficient absorption of electromagnetic waves of a specific hand direction can be achieved, while electromagnetic waves of the other hand direction are reflected or transmitted. This selective absorption is achieved through the electromagnetic effect caused by the geometric asymmetry of the structure, thereby producing significant circular dichroism at the operating wavelength. This method has important application prospects in the fields of chiral imaging and chiral detection. However, the structure of traditional chiral absorbers is relatively fixed. Once the device is determined, its CD is not adjustable and the bandwidth is narrow, which restricts the application of chiral absorbers. Therefore, there is an urgent need to develop a terahertz broadband chiral absorber with a simple structure, easy production, and flexible tunability to meet the needs of practical terahertz applications. Summary of the Invention

[0006] The first purpose of the present invention is to propose a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. The terahertz chiral absorber can have a circular dichroism (CD) value greater than 0.8 in the range of 5.36THz to 7.69THz, and its mirror enantiomer can also achieve a corresponding opposite CD spectrum. It has the advantages of high CD, dynamic tunability and simple structure.

[0007] The second objective of the present invention is to propose a preparation method of a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide.

[0008] The first technical solution adopted by the present invention is a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. The absorber is composed of a periodic array of M×N multilayer absorption units. The absorption units are distributed in an M×N two-dimensional manner, where M and N are both positive integers. The absorption unit includes a metal substrate, a dielectric layer and a resonance layer arranged in sequence from bottom to top; The metal substrate and the dielectric layer are both rectangular; the resonance layer comprises a J-shaped metal patch, and an inverted T-shaped vanadium dioxide patch is arranged at one end of the J-shaped metal patch.

[0009] The present invention is also characterized in that: The metal substrate is made of gold, with a conductivity of 4.56×10 7 S / m, length a is 17µm-19µm, width b is 15µm-17µm, and thickness d is 0.1µm -0.2µm.

[0010] The material of the dielectric layer is polyimide, with a relative dielectric constant of 3.5. The length Py is 17µm-19µm, the width Px is 15µm-17µm, and the thickness h is 4.4µm-4.6µm.

[0011] The material of the J-shaped metal patch is gold, and its conductivity is 4.56×107 S / m; the thickness t1 of the J-shaped metal patch is 2.1µm-2.3µm.

[0012] The J-shaped metal patch is composed of a semicircular patch and a rectangular patch, wherein the first end of the semicircular patch is connected to the rectangular patch, and the second end of the semicircular patch is connected to the inverted T-shaped vanadium dioxide patch; The inner ring radius R of the semicircular ring patch is 5.1µm-5.3µm, and the ring width W3 is 0.9µm-1.1µm; the width W4 of the rectangular patch is equal to the ring width W3 of the semicircular ring patch, and the length L3 of the rectangular patch is 6.9µm-7.1µm; The inverted T-shaped vanadium dioxide patch has a thickness t2 of 0.24µm to 0.26µm. The inverted T-shaped vanadium dioxide patch consists of a horizontal arm and a vertical arm, one end of the vertical arm is connected to the arm body of the horizontal arm, and the arm body of the horizontal arm is also connected to the second end of the semicircular ring patch; Among them, the length L1 of the horizontal arm is 4.7µm-4.9µm, and the width W1 is 0.5µm-0.7µm; the length L2 of the vertical arm is 2.3µm-2.5µm, and the width W2 is 0.7µm-0.9µm; The offset distance S between the vertical arm and one end of the horizontal arm is 2.3µm-2.5µm.

[0013] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase, and the electrical conductivity σ is 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase, and the electrical conductivity σ is 200,000 S / m.

[0014] The second technical solution adopted by the present invention is a method for preparing the above-mentioned dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide, which specifically comprises the following steps: Step 1, preparation of metal substrate; Step 2: Deposition of dielectric layer; Step 3: Preparation of top J-shaped metal patch; Step 4: Preparation of the top inverted T-shaped vanadium dioxide patch.

[0015] The present invention is also characterized in that: Step 1 is as follows: Step 1.1, substrate cleaning: High-purity silicon was used as the substrate and ultrasonically cleaned with acetone, ethanol, and deionized water for 10-15 minutes to remove surface contaminants. After drying with nitrogen, the substrate was dried in an oven at 110-120°C for 30-40 minutes. Step 1.2, metal film deposition: Gold thin films were deposited using electron beam evaporation; Step 1.3, annealing treatment: Annealing at 300°C~350°C for 30min-40min to improve the crystallization quality and conductivity of the gold film to obtain a metal substrate.

[0016] Step 2 is as follows: Step 2.1, spin coating of polyimide dielectric layer: Spin-coat the polyimide precursor solution on the underlying gold film, and obtain the desired dielectric layer thickness by precisely controlling the spin-coating speed and time; Step 2.2, curing treatment: Curing at 150-160°C for 1-2 hours ensures the formation of a stable polyimide film. Strictly control the curing process to ensure that the film is flat, free of bubbles and stress cracks, and obtain a dielectric layer on the metal substrate.

[0017] Step 3 is as follows: Step 3.1, photolithography patterning: On the cured polyimide surface, the designed J-shaped metal structure pattern is defined using electron beam lithography technology; Step 3.2, gold thin film deposition: Deposit a thin gold film using electron beam evaporation; Step 3.3, peeling and forming: The photoresist and the excess gold film on it are removed using a lift-off method, leaving behind the designed gold micro-nanostructure to obtain a J-shaped metal patch; Step 4 is as follows: Step 4.1: Photolithography to define the vanadium dioxide area: After the top gold structure is prepared, an inverted T-shaped vanadium dioxide pattern area is defined at a pre-designed position by photolithography; Step 4.2, vanadium dioxide thin film deposition: Pulsed laser deposition is used to deposit a vanadium dioxide thin film on a designated area; Step 4.3, peeling and forming: The photoresist and the excess vanadium dioxide film thereon are removed using a lift-off method, leaving behind the designed structure to obtain an inverted T-shaped vanadium dioxide patch.

[0018] The beneficial effects of the present invention are: (1) The absorption unit of the dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide in the present invention is composed of a metal substrate, a dielectric layer, and a top resonant layer. By introducing a J-shaped metal gold and an inverted T-shaped vanadium dioxide patch, two materials with different conductivity are combined to form a chiral structure, thereby generating a strong coupling effect, promoting the strong electromagnetic response of the resonant structure to the excitation of left-handed circularly polarized waves (LCP), resulting in a huge absorption difference of circularly polarized waves of different rotation directions (perfect absorption of LCP but almost no absorption of RCP), and having a circular dichroism (CD) value greater than 0.8 in the range of 5.36THz to 7.69THz. Its mirror image enantiomer can also achieve the corresponding opposite CD spectrum, with the advantages of high CD, dynamic tunability and simple structure.

[0019] (2) The dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide of the present invention can change the conductivity of the vanadium dioxide patch in the resonance layer by changing the temperature, thereby adjusting the impedance characteristics of the entire terahertz chiral absorber, so that the CD value can be continuously adjusted between 0 and 0.932; (3) The dynamic tunable chiral terahertz broadband absorber based on vanadium dioxide of the present invention has a mirror image enantiomer that can achieve the opposite spin-selective absorption (perfectly absorbs RCP but almost no absorption of LCP). This opposite CD characteristic makes it have good application prospects in the fields of digital coding metasurfaces, terahertz imaging, optical information encryption, etc.

[0020] (4) The preparation method of the present invention is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the three-dimensional structure of the chiral terahertz broadband absorber of the present invention; Figure 2 This is a front view of the absorption unit in the chiral terahertz broadband absorber of the present invention; Figure 3 Schematic diagram of the three-dimensional structural unit of the absorption unit in the chiral terahertz broadband absorber of the present invention; Figure 4 Schematic diagram of the three-dimensional structural unit of the mirror image enantiomer of the absorption unit in the chiral terahertz broadband absorber of the present invention; Figure 5 is the cross-polarization spectrum obtained when the circularly polarized wave is incident on the proposed chiral broadband absorber along the positive direction of the Z axis in Example 1 of the present invention; Figure 6 is the co-polarization reflection spectrum obtained when a circularly polarized wave is incident on the mirror antipodes of the proposed chiral broadband absorber along the positive direction of the Z axis in Example 1 of the present invention; Figure 7 is the absorption spectrum of the absorber of Example 1 of the present invention; Figure 8is the circular dichroism spectrum of the absorber of Example 1 of the present invention; Figure 9 is the absorption spectrum of the mirror image enantiomer of the absorber in Example 1 of the present invention; Figure 10 is the circular dichroism spectrum of the mirror image enantiomer of the absorber in Example 1 of the present invention; Figure 11 is the electric field distribution of the resonant layer of the absorber of Example 1 of the present invention under left-handed light incidence; Figure 12 is the electric field distribution of the resonant layer of the absorber of Example 1 of the present invention under right-handed light incidence; Figure 13 is the electric field distribution of the resonant layer of the absorber mirror enantiomer under left-handed light incidence in Example 1 of the present invention; Figure 14 is the electric field distribution of the resonant layer of the absorber mirror enantiomer under right-handed light incidence in Example 1 of the present invention; Figure 15 The LCP absorption spectrum of the absorber according to Example 1 of the present invention changes with the conductivity of vanadium dioxide; Figure 16 is the RCP absorption spectrum of the absorber according to Example 1 of the present invention as the conductivity of vanadium dioxide changes; Figure 17 : CD spectrum of the absorber according to Example 1 of the present invention as the conductivity of vanadium dioxide changes; Figure 18 3 is a diagram showing the influence of the absorber of Example 1 of the present invention on the CD spectrum as the incident angle of the circularly polarized wave changes.

[0022] In the figure, 1. metal substrate, 2. dielectric layer, 3. resonant layer, 4. resonant layer A; 3-1. J-shaped metal patch, 3-2. Inverted T-shaped vanadium dioxide patch; 3-1-1. Semicircular patch, 3-1-2. Rectangular patch; 3-2-1. Horizontal arm, 3-2-2. Vertical arm. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] The present invention provides a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. The absorber is composed of a periodic array of M×N multilayer absorption units, and the absorption units are distributed in an M×N two-dimensional manner, where M and N are both positive integers. The absorption unit includes a metal substrate 1, a dielectric layer 2 and a resonance layer 3 arranged in sequence from bottom to top; The metal substrate 1 and the dielectric layer 2 are both rectangular; the resonant layer 3 includes a J-shaped metal patch 3-1, and an inverted T-shaped vanadium dioxide patch 3-2 is provided at one end of the J-shaped metal patch 3-1.

[0025] The material of the metal substrate 1 is gold, and the electrical conductivity is 4.56×10 7 S / m, length a is 17µm-19µm, width b is 15µm-17µm, and thickness d is 0.1µm-0.2µm.

[0026] The dielectric layer 2 is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 17µm-19µm, a width Px of 15µm-17µm, and a thickness h of 4.4µm-4.6µm.

[0027] The material of the J-shaped metal patch 3-1 is gold, and its conductivity is 4.56×10 7 S / m; the thickness t1 of the J-shaped metal patch 3-1 is 2.1µm-2.3µm.

[0028] The J-shaped metal patch 3-1 is composed of a semicircular ring patch 3-1-1 and a rectangular patch 3-1-2. The first end of the semicircular ring patch 3-1-1 is connected to the rectangular patch 3-1-2, and the second end of the semicircular ring patch 3-1-1 is connected to the inverted T-shaped vanadium dioxide patch 3-2. Among them, the inner ring radius R of the semicircular ring patch 3-1-1 is 5.1µm-5.3µm, and the ring width W3 is 0.9µm-1.1µm; the width W4 of the rectangular patch 3-1-2 is equal to the ring width W3 of the semicircular ring patch 3-1-1, and the length L3 of the rectangular patch 3-1-2 is 6.9µm-7.1µm; The thickness t2 of the inverted T-shaped vanadium dioxide patch 3-2 is 0.24µm-0.26µm. The inverted T-shaped vanadium dioxide patch 3-2 is composed of a horizontal arm 3-2-1 and a vertical arm 3-2-2. One end of the vertical arm 3-2-2 is connected to the arm body of the horizontal arm 3-2-1. The arm body of the horizontal arm 3-2-1 is also connected to the second end of the semicircular ring patch 3-1-1. Among them, the length L1 of the horizontal arm 3-2-1 is 4.7µm-4.9µm, and the width W1 is 0.5µm-0.7µm; the length L2 of the vertical arm 3-2-2 is 2.3µm-2.5µm, and the width W2 is 0.7µm-0.9µm; The offset distance S between the vertical arm 3-2-2 and one end of the horizontal arm 3-2-1 is 2.3µm-2.5µm.

[0029] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase, and the electrical conductivity σ is 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase, and the electrical conductivity σ is 200,000 S / m.

[0030] The present invention also provides a method for preparing a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide, which specifically comprises the following steps: Step 1, preparation of a metal substrate 1; Step 1 is as follows: Step 1.1, substrate cleaning: High-purity silicon was used as the substrate and ultrasonically cleaned with acetone, ethanol, and deionized water for 10-15 minutes to remove surface contaminants. After drying with nitrogen, the substrate was dried in an oven at 110-120°C for 30-40 minutes. Step 1.2, metal film deposition: Gold thin films were deposited using electron beam evaporation; Step 1.3, annealing treatment: Annealing is performed at 300° C. to 350° C. for 30 min to 40 min to improve the crystallization quality and conductivity of the gold film, thereby obtaining a metal substrate 1 .

[0031] Step 2, deposition of dielectric layer 2; Step 2 is as follows: Step 2.1, spin coating of polyimide dielectric layer: Spin-coat the polyimide precursor solution on the underlying gold film, and obtain the desired dielectric layer thickness by precisely controlling the spin-coating speed and time; Step 2.2, curing treatment: Curing is performed at 150° C.-160° C. for 1 h-2 h to ensure the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks, and a dielectric layer 2 is obtained on the metal substrate 1.

[0032] Step 3: Preparation of top J-shaped metal patch 3-1; Step 3 is as follows: Step 3.1, photolithography patterning: On the cured polyimide surface, the designed J-shaped metal structure pattern is defined using electron beam lithography technology; Step 3.2, gold thin film deposition: Deposit a thin gold film using electron beam evaporation; Step 3.3, peeling and forming: The photoresist and the excess gold film thereon are removed by a lift-off method, leaving behind the designed gold micro-nanostructure to obtain a J-shaped metal patch 3-1; Step 4: Preparation of the top inverted T-shaped vanadium dioxide patch 3-2.

[0033] Step 4 is as follows: Step 4.1: Photolithography to define the vanadium dioxide area: After the top gold structure is prepared, an inverted T-shaped vanadium dioxide pattern area is defined at a pre-designed position by photolithography; Step 4.2, vanadium dioxide thin film deposition: Pulsed laser deposition is used to deposit a vanadium dioxide thin film on a designated area; Step 4.3, peeling and forming: The photoresist and the excess vanadium dioxide film thereon are removed using a lift-off method, leaving behind the designed structure to obtain an inverted T-shaped vanadium dioxide patch 3-2.

[0034] Example 1: like Figure 1-Figure 3 As shown, this embodiment provides a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. The tunable THz absorber is composed of 3×3 structural units arranged periodically in the XY plane, and the number of units does not affect the overall absorption performance. The geometric center of the structural unit is taken as point O, and the two mutually perpendicular sides along the horizontal and vertical directions passing through this point are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. The structural unit has chiral characteristics. Each absorption unit includes a metal substrate 1, a dielectric layer 2 and a resonant layer 3 arranged in sequence from bottom to top; The metal substrate 1 and the dielectric layer 2 are both rectangular; the resonant layer 3 includes a J-shaped metal patch 3-1, and an inverted T-shaped vanadium dioxide patch 3-2 is provided at one end of the J-shaped metal patch 3-1.

[0035] The material of the J-shaped metal unit 3-1 is gold, and its electrical conductivity is 4.56×10 7 S / m, its thickness t1 is 2.2µm; the J-shaped metal patch 3-1 is composed of a semicircular ring patch 3-1-1 and a rectangular patch 3-1-2, the first end of the semicircular ring patch 3-1-1 is connected to the rectangular patch 3-1-2, and the second end of the semicircular ring patch 3-1-1 is connected to the inverted T-shaped vanadium dioxide patch 3-2; The inner ring radius R of the semicircular ring patch 3-1-1 is 5.2µm, and the ring width W3 is 1.0µm; the width W4 of the rectangular patch 3-1-2 is equal to the ring width W3 of the semicircular ring patch 3-1-1, and the length L3 of the rectangular patch 3-1-2 is 7.0µm; The thickness t2 of the inverted T-shaped vanadium dioxide patch 3-2 is 0.25µm. The inverted T-shaped vanadium dioxide patch 3-2 is composed of a horizontal arm 3-2-1 and a vertical arm 3-2-2. One end of the vertical arm 3-2-2 is connected to the arm body of the horizontal arm 3-2-1. The arm body of the horizontal arm 3-2-1 is also connected to the second end of the semicircular ring patch 3-1-1. Among them, the length L1 of the horizontal arm 3-2-1 is 4.8µm, and the width W1 is 0.6µm; the length L2 of the vertical arm 3-2-2 is 2.4µm, and the width W2 is 0.8µm; The offset distance S between the vertical arm 3-2-2 and one end of the horizontal arm 3-2-1 is 2.4µm.

[0036] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase with an electrical conductivity σ of 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase with an electrical conductivity σ of 200,000 S / m.

[0037] The dielectric layer 2 is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 18 μm, a width Px of 16 μm, and a thickness h of 4.5 μm.

[0038] The material of the metal substrate 1 is gold, and the electrical conductivity is 4.56×10 7 S / m, length a is 18µm, width b is 16µm, and thickness d is 0.15µm.

[0039] The thickness d is much larger than the skin depth of gold in the terahertz band, ensuring that the transmittance T of the absorber is 0.

[0040] The preparation method of the above-mentioned vanadium dioxide dynamically tunable chiral terahertz broadband absorber is as follows: Step 1, preparation of a metal substrate 1; Step 1 is as follows: Step 1.1, substrate cleaning: High-purity silicon was used as the substrate and ultrasonically cleaned with acetone, ethanol, and deionized water for 10 minutes to remove surface contaminants. After drying with nitrogen, the substrate was dried in an oven at 110°C for 30 minutes. Step 1.2, metal film deposition: Gold thin films were deposited using electron beam evaporation; Step 1.3, annealing treatment: Annealing was performed at 300° C. for 30 minutes to improve the crystallization quality and conductivity of the gold film, thereby obtaining a metal substrate 1 .

[0041] Step 2: Deposition of dielectric layer 2; Step 2 is as follows: Step 2.1, spin coating of polyimide dielectric layer: Spin-coat the polyimide precursor solution on the underlying gold film, and obtain the desired dielectric layer thickness by precisely controlling the spin-coating speed and time; Step 2.2, curing treatment: The film was cured at 150° C. for 1 h to ensure the formation of a stable polyimide film. The curing process was strictly controlled to ensure that the film was flat, free of bubbles and stress cracks, and a dielectric layer 2 was obtained on the metal substrate 1.

[0042] Step 3: Preparation of top J-shaped metal patch 3-1; Step 3 is as follows: Step 3.1, photolithography patterning: On the cured polyimide surface, the designed J-shaped metal structure pattern is defined using electron beam lithography technology; Step 3.2, gold thin film deposition: Deposit a thin gold film using electron beam evaporation; Step 3.3, peeling and forming: The photoresist and the excess gold film thereon are removed by a lift-off method, leaving behind the designed gold micro-nanostructure to obtain a J-shaped metal patch 3-1; Step 4: Preparation of the top inverted T-shaped vanadium dioxide patch 3-2.

[0043] Step 4 is as follows: Step 4.1: Photolithography to define the vanadium dioxide area: After the top gold structure is prepared, an inverted T-shaped vanadium dioxide pattern area is defined at a pre-designed position by photolithography; Step 4.2, vanadium dioxide thin film deposition: Pulsed laser deposition is used to deposit a vanadium dioxide thin film on a designated area; Step 4.3, peeling and forming: The photoresist and the excess vanadium dioxide film thereon are removed using a lift-off method, leaving behind the designed structure to obtain an inverted T-shaped vanadium dioxide patch 3-2.

[0044] like Figure 4 As shown, the uppermost resonance layer A 4 of the mirror image enantiomer of the absorption unit in the chiral terahertz broadband absorber and the resonance layer 3 of Example 1 are mirror image enantiomers of each other; Figure 5-Figure 6 Under the irradiation of LCP and RCP light, the absorber unit and its mirror image unit (such as Figure 4 (shown) Cross-polarization and co-polarization reflectance spectra of two chiral absorbers; according to Figure 5 It can be seen that the cross-polarization reflection coefficients are equal, but the co-polarization reflection coefficients differ significantly, which is the reason for the strong circular dichroism effect. Therefore, the absorber proposed in this embodiment has excellent selective absorption of left-handed circularly polarized waves. At the same time, it has efficient broadband reflectivity for incident right-handed circularly polarized waves without changing their rotational direction.

[0045] according to Figure 6 It can be seen that the cross-polarization reflection coefficients are equal, but the co-polarization reflection coefficients are very different and Figure 5 The mirror image of the absorber in this embodiment has excellent selective absorption of right-handed circularly polarized waves. At the same time, it has high broadband reflectivity for incident left-handed circularly polarized waves without changing their rotation direction.

[0046] Figure 7-10 The absorption spectrum and CD spectrum of the absorber obtained in this example and its mirror image enantiomer are shown in FIG.

[0047] according to Figure 7 and Figure 8 It can be seen that the absorber of this embodiment can efficiently absorb left-handed circularly polarized waves, with an absorption rate of up to 99% at a frequency of f = 6.436 THz. However, its absorption rate for right-handed circularly polarized waves is lower, only 5.6% at a frequency of f = 6.436 THz. LCP -A RCP Calculations show that within the frequency range of 5.36 THz to 7.69 THz, the circular dichroism (CD) value of the absorber of this embodiment is greater than 0.8, and reaches a maximum value of 0.934 at a frequency of f = 6.436 THz.

[0048] according to Figure 9 and Figure 10 It can be seen that the mirror image can efficiently absorb right-handed circularly polarized waves, with an absorption rate of up to 99% at a frequency of f = 6.436THz. However, its absorption rate for left-handed circularly polarized waves is lower, only 5.6% at a frequency of f = 6.436THz. LCP -A RCP Calculations show that in the frequency range of 5.36 THz to 7.69 THz, the circular dichroism (CD) value of its mirror enantiomer is less than -0.8, reaching a minimum value of -0.934 at a frequency of f = 6.436 THz.

[0049] from Figure 7-10 It is not difficult to see that the absorber obtained in this embodiment and its mirror image antipodes have exactly opposite selective absorption properties for circularly polarized waves. Therefore, by rationally utilizing the opposite CD properties of the two, they can be used to realize applications such as digital coding metasurfaces, terahertz imaging, and optical information encryption. Therefore, this invention has promising application prospects.

[0050] In order to further study the physical mechanism of the high circular dichroism (CD) of the absorber and its mirror image antipodes obtained in this example, the top electric field distribution of each absorber at the peak frequency when vanadium dioxide is in the metallic state was studied. The results are shown in Figure 2. Figure 11-14 As shown. Figure 11It can be seen that when the incident light is left-hand circularly polarized (LCP), the electric field is mainly distributed at the right end of the horizontal rod of the vanadium dioxide patch, the upper end of the vertical rod, and the contact surface between the left end of the horizontal rod and the J-shaped metal unit. The high absorption here is mainly caused by the strong electric dipole resonance and magnetic dipole resonance. Figure 12 It can be seen that when the incident light is right-hand circularly polarized (RCP), the electric field is mainly distributed at the bottom right side of the ring of the J-shaped metal unit and the top of the rectangular metal patch, and the electric field intensity is relatively Figure 7 The weak absorption here is mainly caused by the weak electric dipole resonance, electric quadrupole resonance, and magnetic dipole resonance. Therefore, when the circularly polarized wave is incident vertically on the absorber of this embodiment, LCP is perfectly absorbed and RCP is almost not absorbed, thus achieving perfect spin-selective absorption of circularly polarized light. The electric field distribution of the mirror image enantiomer when the left-handed circularly polarized wave (LCP) and the right-handed circularly polarized wave (RCP) are respectively as follows: Figure 13 、 Figure 14 The electric field distribution is opposite to that of the absorber in this embodiment at LCP and RCP, which also results in that when the circularly polarized wave is vertically incident, the RCP is perfectly absorbed and the LCP is almost not absorbed, thus achieving a perfect spin-selective absorption effect that is exactly opposite to that of the absorber in this embodiment.

[0051] In order to investigate the dynamic tuning capability of the absorber, Figure 15-17 The effects of vanadium dioxide conductivity on the LCP absorption spectrum, RCP absorption spectrum, and CD spectrum of the absorber of this embodiment are given respectively. Figure 15-16 It can be seen that when the conductivity σ of vanadium dioxide changes between 200S / m and 200000S / m, the overall LCP absorption rate gradually increases, while the overall increase in RCP absorption rate is relatively weak. Figure 17 It can be seen that the CD spectrum gradually increases when the conductivity σ of vanadium dioxide changes between 200 S / m and 200,000 S / m. Therefore, the absorber has the characteristics of dynamic tunability.

[0052] In order to study the effect of the incident angle θ on the CD performance, the CD values ​​of the absorber of this embodiment were calculated with θ ranging from 0° to 80° and other parameters kept unchanged. Figure 18As shown in the figure, it can be observed that as the incident angle θ increases from 0° to 20°, the CD spectrum bandwidth decreases slightly but still maintains broadband characteristics, with the CD peak stable above 0.8. As θ continues to increase to 80°, the influence of CD on the change in θ becomes greater, the CD spectrum bandwidth gradually decreases, and reverse CD is generated in the 4THz-5THz range. In addition, a new narrowband CD is formed in the 9-10THz range. This phenomenon is caused by the fact that when the circularly polarized wave is incident perpendicularly, the broad CD spectrum is primarily the result of the combined effect of the electric and magnetic dipole resonances excited by the absorber's own chirality. However, when the circularly polarized wave is incident at an angle, the effect of external chirality is generated, which disrupts the original electromagnetic response and thus changes the absorption effect. Therefore, as θ increases, the bandwidth decreases, and even reverse CD and narrowband CD are generated. In summary, the absorber of the present invention has the advantage of supporting oblique incident electromagnetic waves within 0-20° while maintaining broadband absorption.

[0053] Example 2: This embodiment provides a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. The tunable THz absorber is composed of 3×3 structural units arranged periodically in the XY plane, and the number of units does not affect the overall absorption performance. The geometric center of the structural unit is taken as point O, and the two mutually perpendicular sides passing through this point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. The structural unit has chiral characteristics. Each absorption unit includes a metal substrate 1, a dielectric layer 2 and a resonant layer 3 arranged in sequence from bottom to top; The metal substrate 1 and the dielectric layer 2 are both rectangular; the resonant layer 3 includes a J-shaped metal patch 3-1, and an inverted T-shaped vanadium dioxide patch 3-2 is provided at one end of the J-shaped metal patch 3-1.

[0054] The material of the J-shaped metal unit 3-1 is gold, and its electrical conductivity is 4.56×10 7 S / m, its thickness t1 is 2.1µm; the J-shaped metal patch 3-1 is composed of a semicircular ring patch 3-1-1 and a rectangular patch 3-1-2, the first end of the semicircular ring patch 3-1-1 is connected to the rectangular patch 3-1-2, and the second end of the semicircular ring patch 3-1-1 is connected to the inverted T-shaped vanadium dioxide patch 3-2; Among them, the inner ring radius R of the semicircular ring patch 3-1-1 is 5.1µm, and the ring width W3 is 0.9µm; the width W4 of the rectangular patch 3-1-2 is equal to the ring width W3 of the semicircular ring patch 3-1-1, and the length L3 of the rectangular patch 3-1-2 is 6.9µm; The thickness t2 of the inverted T-shaped vanadium dioxide patch 3-2 is 0.24µm. The inverted T-shaped vanadium dioxide patch 3-2 is composed of a horizontal arm 3-2-1 and a vertical arm 3-2-2. One end of the vertical arm 3-2-2 is connected to the arm body of the horizontal arm 3-2-1. The arm body of the horizontal arm 3-2-1 is also connected to the second end of the semicircular ring patch 3-1-1. Among them, the length L1 of the horizontal arm 3-2-1 is 4.7µm, and the width W1 is 0.5µm; the length L2 of the vertical arm 3-2-2 is 2.3µm, and the width W2 is 0.7µm; The offset distance S between the vertical arm 3-2-2 and one end of the horizontal arm 3-2-1 is 2.3µm.

[0055] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase with an electrical conductivity σ of 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase with an electrical conductivity σ of 200,000 S / m.

[0056] The dielectric layer 2 is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 17 μm, a width Px of 15 μm, and a thickness h of 4.4 μm.

[0057] The material of the metal substrate 1 is gold, and the electrical conductivity is 4.56×10 7 The absorber has a length a of 17µm, a width b of 15µm, and a thickness d of 0.14µm. The thickness d is much larger than the skin depth of gold in the terahertz band to ensure that the transmittance T of the absorber is 0.

[0058] The preparation method of the above-mentioned vanadium dioxide dynamically tunable chiral terahertz broadband absorber is as follows: Step 1, preparation of a metal substrate 1; Step 1 is as follows: Step 1.1, substrate cleaning: High-purity silicon was used as the substrate and ultrasonically cleaned with acetone, ethanol, and deionized water for 12 minutes to remove surface contaminants. After drying with nitrogen, the substrate was dried in an oven at 115°C for 35 minutes. Step 1.2, metal film deposition: Gold thin films were deposited using electron beam evaporation; Step 1.3, annealing treatment: Annealing was performed at 320° C. for 35 minutes to improve the crystallization quality and conductivity of the gold film, thereby obtaining a metal substrate 1 .

[0059] Step 2: Deposition of dielectric layer 2; Step 2 is as follows: Step 2.1, spin coating of polyimide dielectric layer: Spin-coat the polyimide precursor solution on the underlying gold film, and obtain the desired dielectric layer thickness by precisely controlling the spin-coating speed and time; Step 2.2, curing treatment: The film was cured at 155° C. for 1.5 hours to ensure the formation of a stable polyimide film. The curing process was strictly controlled to ensure that the film was flat, free of bubbles and stress cracks, and a dielectric layer 2 was obtained on the metal substrate 1 .

[0060] Step 3: Preparation of top J-shaped metal patch 3-1; Step 3 is as follows: Step 3.1, photolithography patterning: On the cured polyimide surface, the designed J-shaped metal structure pattern is defined using electron beam lithography technology; Step 3.2, gold thin film deposition: Deposit a thin gold film using electron beam evaporation; Step 3.3, peeling and forming: The photoresist and the excess gold film thereon are removed by a lift-off method, leaving behind the designed gold micro-nanostructure to obtain a J-shaped metal patch 3-1; Step 4: Preparation of the top inverted T-shaped vanadium dioxide patch 3-2.

[0061] Step 4 is as follows: Step 4.1: Photolithography to define the vanadium dioxide area: After the top gold structure is prepared, an inverted T-shaped vanadium dioxide pattern area is defined at a pre-designed position by photolithography; Step 4.2, vanadium dioxide thin film deposition: Pulsed laser deposition is used to deposit a vanadium dioxide thin film on a designated area; Step 4.3, peeling and forming: The photoresist and the excess vanadium dioxide film thereon are removed using a lift-off method, leaving behind the designed structure to obtain an inverted T-shaped vanadium dioxide patch 3-2.

[0062] Example 3: This embodiment provides a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. This tunable THz absorber is composed of 3×3 structural units arranged periodically in the XY plane, and the number of units does not affect the overall absorption performance. The geometric center of the structural unit is point O, and the two mutually perpendicular sides passing through this point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. The structural unit has chiral characteristics, and each absorption unit includes a metal substrate 1, a dielectric layer 2, and a resonant layer 3 arranged in order from bottom to top. The metal substrate 1 and the dielectric layer 2 are both rectangular; the resonant layer 3 includes a J-shaped metal patch 3-1, and an inverted T-shaped vanadium dioxide patch 3-2 is provided at one end of the J-shaped metal patch 3-1.

[0063] The material of the J-shaped metal unit 3-1 is gold, and its electrical conductivity is 4.56×10 7 S / m, its thickness t1 is 2.3µm; the J-shaped metal patch 3-1 is composed of a semicircular ring patch 3-1-1 and a rectangular patch 3-1-2, the first end of the semicircular ring patch 3-1-1 is connected to the rectangular patch 3-1-2, and the second end of the semicircular ring patch 3-1-1 is connected to the inverted T-shaped vanadium dioxide patch 3-2; The inner ring radius R of the semicircular ring patch 3-1-1 is 5.3µm, and the ring width W3 is 1.1µm; the width W4 of the rectangular patch 3-1-2 is equal to the ring width W3 of the semicircular ring patch 3-1-1, and the length L3 of the rectangular patch 3-1-2 is 7.1µm; The thickness t2 of the inverted T-shaped vanadium dioxide patch 3-2 is 0.26µm. The inverted T-shaped vanadium dioxide patch 3-2 is composed of a horizontal arm 3-2-1 and a vertical arm 3-2-2. One end of the vertical arm 3-2-2 is connected to the arm body of the horizontal arm 3-2-1. The arm body of the horizontal arm 3-2-1 is also connected to the second end of the semicircular ring patch 3-1-1. Among them, the length L1 of the horizontal arm 3-2-1 is 4.9µm, and the width W1 is 0.7µm; the length L2 of the vertical arm 3-2-2 is 2.5µm, and the width W2 is 0.9µm; The offset distance S between the vertical arm 3-2-2 and one end of the horizontal arm 3-2-1 is 2.5µm.

[0064] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase with an electrical conductivity σ of 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase with an electrical conductivity σ of 200,000 S / m.

[0065] The dielectric layer 2 is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 19 μm, a width Px of 17 μm, and a thickness h of 4.6 μm.

[0066] The material of the metal substrate 1 is gold, and the electrical conductivity is 4.56×10 7 The absorber has a length a of 19µm, a width b of 17µm, and a thickness d of 0.16µm. The thickness d is much larger than the skin depth of gold in the terahertz band to ensure that the transmittance T of the absorber is 0.

[0067] The preparation method of the above-mentioned vanadium dioxide dynamically tunable chiral terahertz broadband absorber is as follows: Step 1, preparation of a metal substrate 1; Step 1 is as follows: Step 1.1, substrate cleaning: High-purity silicon was used as the substrate and ultrasonically cleaned with acetone, ethanol, and deionized water for 15 minutes to remove surface contaminants. After drying with nitrogen, the substrate was dried in an oven at 120°C for 40 minutes. Step 1.2, metal film deposition: Gold thin films were deposited using electron beam evaporation; Step 1.3, annealing treatment: Annealing was performed at 350° C. for 40 minutes to improve the crystallization quality and conductivity of the gold film, thereby obtaining a metal substrate 1 .

[0068] Step 2, deposition of dielectric layer 2; Step 2 is as follows: Step 2.1, spin coating of polyimide dielectric layer: Spin-coat the polyimide precursor solution on the underlying gold film, and obtain the desired dielectric layer thickness by precisely controlling the spin-coating speed and time; Step 2.2, curing treatment: The film is cured at 160° C. for 2 hours to ensure the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks, and a dielectric layer 2 is obtained on the metal substrate 1.

[0069] Step 3: Preparation of top J-shaped metal patch 3-1; Step 3 is as follows: Step 3.1, photolithography patterning: On the cured polyimide surface, the designed J-shaped metal structure pattern is defined using electron beam lithography technology; Step 3.2, gold thin film deposition: Deposit a thin gold film using electron beam evaporation; Step 3.3, peeling and forming: The photoresist and the excess gold film thereon are removed by a lift-off method, leaving behind the designed gold micro-nanostructure to obtain a J-shaped metal patch 3-1; Step 4: Preparation of the top inverted T-shaped vanadium dioxide patch 3-2.

[0070] Step 4 is as follows: Step 4.1: Photolithography to define the vanadium dioxide area: After the top gold structure is prepared, an inverted T-shaped vanadium dioxide pattern area is defined at a pre-designed position by photolithography; Step 4.2, vanadium dioxide thin film deposition: Pulsed laser deposition is used to deposit a vanadium dioxide thin film on a designated area; Step 4.3, peeling and forming: The photoresist and the excess vanadium dioxide film thereon are removed using a lift-off method, leaving behind the designed structure to obtain an inverted T-shaped vanadium dioxide patch 3-2.

[0071] Example 4: This embodiment provides a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. The tunable THz absorber is composed of 3×3 structural units arranged periodically in the XY plane, and the number of units does not affect the overall absorption performance. The geometric center of the structural unit is taken as point O, and the two mutually perpendicular sides passing through this point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. The structural unit has chiral characteristics. Each absorption unit includes a metal substrate 1, a dielectric layer 2 and a resonant layer 3 arranged in sequence from bottom to top; The metal substrate 1 and the dielectric layer 2 are both rectangular; the resonant layer 3 includes a J-shaped metal patch 3-1, and an inverted T-shaped vanadium dioxide patch 3-2 is provided at one end of the J-shaped metal patch 3-1.

[0072] The material of the J-shaped metal unit 3-1 is gold, and its electrical conductivity is 4.56×10 7 S / m, its thickness t1 is 2.25µm; the J-shaped metal patch 3-1 is composed of a semicircular ring patch 3-1-1 and a rectangular patch 3-1-2, the first end of the semicircular ring patch 3-1-1 is connected to the rectangular patch 3-1-2, and the second end of the semicircular ring patch 3-1-1 is connected to the inverted T-shaped vanadium dioxide patch 3-2; The inner ring radius R of the semicircular ring patch 3-1-1 is 5.25µm, and the ring width W3 is 1.05µm; the width W4 of the rectangular patch 3-1-2 is equal to the ring width W3 of the semicircular ring patch 3-1-1, and the length L3 of the rectangular patch 3-1-2 is 7.05µm; The thickness t2 of the inverted T-shaped vanadium dioxide patch 3-2 is 0.255µm. The inverted T-shaped vanadium dioxide patch 3-2 is composed of a horizontal arm 3-2-1 and a vertical arm 3-2-2. One end of the vertical arm 3-2-2 is connected to the arm body of the horizontal arm 3-2-1. The arm body of the horizontal arm 3-2-1 is also connected to the second end of the semicircular ring patch 3-1-1. Among them, the length L1 of the horizontal arm 3-2-1 is 4.85µm, and the width W1 is 0.65µm; the length L2 of the vertical arm 3-2-2 is 2.4µm, and the width W2 is 0.85µm; The offset distance S between the vertical arm 3-2-2 and one end of the horizontal arm 3-2-1 is 2.3µm.

[0073] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase with an electrical conductivity σ of 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase with an electrical conductivity σ of 200,000 S / m.

[0074] The dielectric layer 2 is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 18.5 μm, a width Px of 16.5 μm, and a thickness h of 4.55 μm.

[0075] The material of the metal substrate 1 is gold, and the electrical conductivity is 4.56×10 7 S / m, length a is 18.5µm, width b is 16.5µm, and thickness d is 0.155µm.

[0076] The thickness d is much larger than the skin depth of gold in the terahertz band to ensure that the transmittance T of the absorber is 0.

[0077] Example 5: This embodiment provides a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. The tunable THz absorber is composed of 3×3 structural units arranged periodically in the XY plane. The number of units does not affect the overall absorption performance. The geometric center of the structural unit is taken as point O. The two mutually perpendicular sides passing through this point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. The structural unit has chiral characteristics. Each absorption unit includes a metal substrate 1, a dielectric layer 2 and a resonant layer 3 arranged in sequence from bottom to top; The metal substrate 1 and the dielectric layer 2 are both rectangular; the resonant layer 3 includes a J-shaped metal patch 3-1, and an inverted T-shaped vanadium dioxide patch 3-2 is provided at one end of the J-shaped metal patch 3-1.

[0078] The material of the J-shaped metal unit 3-1 is gold, and its electrical conductivity is 4.56×10 7 S / m, its thickness t1 is 2.15µm; the J-shaped metal patch 3-1 is composed of a semicircular ring patch 3-1-1 and a rectangular patch 3-1-2, the first end of the semicircular ring patch 3-1-1 is connected to the rectangular patch 3-1-2, and the second end of the semicircular ring patch 3-1-1 is connected to the inverted T-shaped vanadium dioxide patch 3-2; Among them, the inner ring radius R of the semicircular ring patch 3-1-1 is 5.15µm, and the ring width W3 is 0.95µm; the width W4 of the rectangular patch 3-1-2 is equal to the ring width W3 of the semicircular ring patch 3-1-1, and the length L3 of the rectangular patch 3-1-2 is 6.95µm; The thickness t2 of the inverted T-shaped vanadium dioxide patch 3-2 is 0.245µm. The inverted T-shaped vanadium dioxide patch 3-2 is composed of a horizontal arm 3-2-1 and a vertical arm 3-2-2. One end of the vertical arm 3-2-2 is connected to the arm body of the horizontal arm 3-2-1. The arm body of the horizontal arm 3-2-1 is also connected to the second end of the semicircular ring patch 3-1-1. Among them, the length L1 of the horizontal arm 3-2-1 is 4.75µm, and the width W1 is 0.55µm; the length L2 of the vertical arm 3-2-2 is 2.35µm, and the width W2 is 0.75µm; The offset distance S between the vertical arm 3-2-2 and one end of the horizontal arm 3-2-1 is 2.5µm.

[0079] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase with an electrical conductivity σ of 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase with an electrical conductivity σ of 200,000 S / m.

[0080] The dielectric layer 2 is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 17.5 μm, a width Px of 15.5 μm, and a thickness h of 4.45 μm.

[0081] The material of the metal substrate 1 is gold, and the electrical conductivity is 4.56×10 7 S / m, length a is 17.5µm, width b is 15.5µm, and thickness d is 0.145µm.

[0082] The thickness d is much larger than the skin depth of gold in the terahertz band to ensure that the transmittance T of the absorber is 0.

[0083] Example 6 This embodiment provides a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. This tunable THz absorber is composed of 3×3 structural units arranged periodically in the XY plane, and the number of units does not affect the overall absorption performance. The geometric center of the structural unit is taken as point O, and the two mutually perpendicular sides passing through this point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. The structural unit has chiral characteristics, and each absorption unit includes a metal substrate 1, a dielectric layer 2, and a resonant layer 3 arranged in order from bottom to top. The metal substrate 1 and the dielectric layer 2 are both rectangular; the resonant layer 3 includes a J-shaped metal patch 3-1, and an inverted T-shaped vanadium dioxide patch 3-2 is provided at one end of the J-shaped metal patch 3-1.

[0084] The material of the J-shaped metal unit 3-1 is gold, and its electrical conductivity is 4.56×10 7S / m, its thickness t1 is 2.2µm; the J-shaped metal patch 3-1 is composed of a semicircular ring patch 3-1-1 and a rectangular patch 3-1-2, the first end of the semicircular ring patch 3-1-1 is connected to the rectangular patch 3-1-2, and the second end of the semicircular ring patch 3-1-1 is connected to the inverted T-shaped vanadium dioxide patch 3-2; The inner ring radius R of the semicircular ring patch 3-1-1 is 5.2µm, and the ring width W3 is 1.0µm; the width W4 of the rectangular patch 3-1-2 is equal to the ring width W3 of the semicircular ring patch 3-1-1, and the length L3 of the rectangular patch 3-1-2 is 7.0µm; The thickness t2 of the inverted T-shaped vanadium dioxide patch 3-2 is 0.25µm. The inverted T-shaped vanadium dioxide patch 3-2 is composed of a horizontal arm 3-2-1 and a vertical arm 3-2-2. One end of the vertical arm 3-2-2 is connected to the arm body of the horizontal arm 3-2-1. The arm body of the horizontal arm 3-2-1 is also connected to the second end of the semicircular ring patch 3-1-1. Among them, the length L1 of the horizontal arm 3-2-1 is 4.8µm, and the width W1 is 0.6µm; the length L2 of the vertical arm 3-2-2 is 2.4µm, and the width W2 is 0.8µm; The offset distance S between the vertical arm 3-2-2 and one end of the horizontal arm 3-2-1 is 2.4µm.

[0085] When the ambient temperature is lower than 340 K, vanadium dioxide is in an insulating phase with an electrical conductivity σ of 200 S / m. When the ambient temperature is higher than 340 K, vanadium dioxide is in a metallic phase with an electrical conductivity σ of 200,000 S / m.

[0086] The dielectric layer 2 is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 18 μm, a width Px of 16 μm, and a thickness h of 4.5 μm.

[0087] The material of the metal substrate 1 is gold, and the electrical conductivity is 4.56×10 7 The absorber has a length of 18 µm, a width of 16 µm, and a thickness of 0.15 µm. The thickness d is much larger than the skin depth of gold in the terahertz band to ensure that the transmittance T of the absorber is 0.

[0088] The present invention presents a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide. By optimizing structural parameters, the absorber's circular dichroism (CD) value remains consistently greater than 0.8 within the frequency range of 5.36 THz to 7.69 THz. Its mirror image enantiomer can achieve opposite CD spectra, and the CD spectrum can be dynamically tuned by varying the conductivity of vanadium dioxide. Furthermore, the absorber and its mirror image enantiomer are both capable of reflecting only one circularly polarized wave without changing the handedness, making them suitable for use as THz broadband filters, digital coding metasurfaces, and other applications. In summary, the absorber of the present invention boasts a simple structure, excellent absorption performance, flexible tunability, and promising application prospects.

Claims

1. A dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide, characterized in that: The absorber is composed of a periodic array of M×N multilayer absorption units, and the absorption units are distributed in an M×N two-dimensional manner, where M and N are both positive integers; The absorption unit comprises a metal substrate (1), a dielectric layer (2) and a resonance layer (3) arranged in sequence from bottom to top; The metal substrate (1) and the dielectric layer (2) are both rectangular; the resonant layer (3) comprises a J-shaped metal patch (3-1), and an inverted T-shaped vanadium dioxide patch (3-2) is provided at one end of the J-shaped metal patch (3-1).

2. The dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 1, characterized in that: The metal substrate (1) is made of gold, and its electrical conductivity is 4.56×10 7 S / m, length a is 17µm-19µm, width b is 15µm-17µm, and thickness d is 0.1µm -0.2µm.

3. The dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 1, characterized in that: The dielectric layer (2) is made of polyimide, has a relative dielectric constant of 3.5, a length Py of 17µm-19µm, a width Px of 15µm-17µm, and a thickness h of 4.4µm-4.6µm.

4. The dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 1, characterized in that: The material of the J-shaped metal patch (3-1) is gold, and its conductivity is 4.56×10 7 S / m; the thickness t1 of the J-shaped metal patch (3-1) is 2.1µm-2.3µm.

5. The dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 4, characterized in that: The J-shaped metal patch (3-1) is composed of a semicircular ring patch (3-1-1) and a rectangular patch (3-1-2), wherein the first end of the semicircular ring patch (3-1-1) is connected to the rectangular patch (3-1-2), and the second end of the semicircular ring patch (3-1-1) is connected to the inverted T-shaped vanadium dioxide patch (3-2); Among them, the inner ring radius R of the semicircular ring patch (3-1-1) is 5.1µm-5.3µm, and the ring width W3 is 0.9µm-1.1µm; the width W4 of the rectangular patch (3-1-2) is equal to the ring width W3 of the semicircular ring patch (3-1-1), and the length L3 of the rectangular patch (3-1-2) is 6.9µm-7.1µm.

6. The dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 5, characterized in that: The thickness t2 of the inverted T-shaped vanadium dioxide patch (3-2) is 0.24µm-0.26µm; the inverted T-shaped vanadium dioxide patch (3-2) is composed of a horizontal arm (3-2-1) and a vertical arm (3-2-2), one end of the vertical arm (3-2-2) is connected to the arm body of the horizontal arm (3-2-1), and the arm body of the horizontal arm (3-2-1) is also connected to the second end of the semicircular ring patch (3-1-1); Among them, the length L1 of the horizontal arm (3-2-1) is 4.7µm-4.9µm, and the width W1 is 0.5µm-0.7µm; the length L2 of the vertical arm (3-2-2) is 2.3µm-2.5µm, and the width W2 is 0.7µm -0.9µm; The offset distance S between the vertical arm (3-2-2) and one end of the horizontal arm (3-2-1) is 2.3µm-2.5µm.

7. The method for preparing a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to any one of claims 1 to 6, characterized in that: The specific steps include: Step 1, preparation of a metal substrate (1); Step 2, deposition of dielectric layer (2); Step 3: Preparation of the top J-shaped metal patch (3-1); Step 4: Preparation of the top inverted T-shaped vanadium dioxide patch (3-2).

8. The method for preparing a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 7, characterized in that: Step 1 is as follows: Step 1.1, substrate cleaning: High-purity silicon was used as the substrate and ultrasonically cleaned with acetone, ethanol, and deionized water for 10-15 minutes to remove surface contaminants. After drying with nitrogen, the substrate was dried in an oven at 110-120°C for 30-40 minutes. Step 1.2, metal film deposition: Gold thin films were deposited using electron beam evaporation; Step 1.3, annealing treatment: Annealing at 300°C to 350°C for 30 min to 40 min to improve the crystallization quality and conductivity of the gold film to obtain a metal substrate (1).

9. The method for preparing a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 8, characterized in that: Step 2 is as follows: Step 2.1, spin coating of polyimide dielectric layer: Spin-coat a polyimide precursor solution on the underlying gold film to obtain the desired dielectric layer thickness; Step 2.2, curing treatment: The film is cured at 150° C. to 160° C. for 1 h to 2 h to obtain a dielectric layer (2) on the metal substrate (1).

10. The method for preparing a dynamically tunable chiral terahertz broadband absorber based on vanadium dioxide according to claim 6, characterized in that: Step 3 is as follows: Step 3.1, photolithography patterning: On the cured polyimide surface, the designed J-shaped metal structure pattern is defined using electron beam lithography technology; Step 3.2, gold thin film deposition: Deposit a thin gold film using electron beam evaporation; Step 3.3, peeling and forming: The photoresist and the excess gold film on it are removed by the lift-off method, leaving behind the designed gold micro-nanostructure to obtain a J-shaped metal patch (3-1); Step 4 is as follows: Step 4.1: Photolithography to define the vanadium dioxide area: After the top gold structure is prepared, an inverted T-shaped vanadium dioxide pattern area is defined at a pre-designed position by photolithography; Step 4.2, vanadium dioxide thin film deposition: Pulsed laser deposition is used to deposit a vanadium dioxide thin film on a designated area; Step 4.3, peeling and forming: The photoresist and the excess vanadium dioxide film thereon are removed by a lift-off method, leaving behind the designed structure to obtain an inverted T-shaped vanadium dioxide patch (3-2).

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