Adjustable terahertz circular dichroism device with asymmetric coupling double-ring structure

Abstract

The invention discloses an adjustable terahertz circular dichroism device with an asymmetric coupling double-ring structure, and belongs to the technical field of terahertz. The adjustable terahertz circular dichroism device with the asymmetric coupling double-ring structure is formed by periodically arranging and splicing a plurality of unit structures, and each unit structure comprises a silicon dioxide substrate and a photosensitive silicon resonator which is arranged on the front surface of the substrate and is internally etched with two asymmetric circular rings with the same parameters. According to the invention, a Brillouin region folding mechanism is combined with mirror symmetry breaking, and the position of the circular ring is changed, so that the circular dichroism and the quality factor of terahertz waves are regulated and controlled, and polarization conversion is realized. The adjustable terahertz circular dichroism device with the asymmetric coupling double-ring structure is simple in structure, the circular dichroism and the quality factor of the device can be regulated and controlled and polarization conversion can be realized only by changing the position of the circular ring, and the adjustable terahertz circular dichroism device is suitable for a future terahertz integrated system.

Description

Technical Field

[0001] This invention relates to the field of terahertz technology, and more particularly to an asymmetric coupled double-ring structure tunable terahertz circular dichroic device. Background Technology

[0002] Terahertz waves, an electromagnetic wave band with unique advantages, lie between infrared light and microwaves. They have broad application prospects in fields such as communication, radar, medical imaging, and security inspection, and have therefore been recognized internationally as one of the top ten technologies that will change the future world. As an emerging technology with enormous potential, terahertz technology is gradually demonstrating its unique value and application prospects in numerous fields. In the field of communication, terahertz waves are characterized by high bandwidth and high speed. This means they can transmit large amounts of data in a short time, making ultra-high-speed wireless communication possible in the future. Compared to traditional communication frequency bands, the terahertz band has more available spectrum resources, potentially solving the current problem of spectrum scarcity in the communication field. Terahertz technology also demonstrates its capabilities in security inspection. Because terahertz waves can penetrate non-polar materials such as clothing and plastics, and have good reflectivity to metals, they can effectively detect dangerous items hidden in people and packages. Compared to traditional security inspection methods, terahertz security inspection has higher accuracy and security, while having minimal radiation impact on the human body. In the medical field, terahertz technology brings new hope for disease diagnosis and treatment. Terahertz waves possess a certain degree of penetrability into biological tissues, enabling the acquisition of characteristic information about biomolecules and thus facilitating early disease diagnosis. For example, in cancer detection, terahertz technology can detect differences between tumor tissue and normal tissue at the molecular level. In materials science, terahertz technology can be used for material characterization and analysis. By measuring the propagation and reflection characteristics of terahertz waves in materials, the electrical, optical, and mechanical properties of the materials can be obtained, providing crucial information for materials research and development and quality control.

[0003] Many substances in nature exhibit chirality, such as proteins, amino acids, and DNA. Therefore, detecting the chirality of substances has become a hot research topic for many scientists. Chiral materials exhibit different absorption characteristics for right- and left-circularly polarized incident waves; this phenomenon is called circular dichroism (CD). CD can be defined as the difference in absorption / reflection of a chiral medium for waves with different circular polarizations; the difference is the circular dichroism. High CD can be achieved through optimized design of the geometry of circular dichroic metasurfaces. However, their inherent ohmic losses and radiation damping often limit the quality factor (Q). To improve this problem, researchers have attempted to introduce continuous-spectrum bound states (BICs) into chiral metasurfaces and utilize symmetry breaking to transform ideal continuous-spectrum bound states into observable Q-BICs, aiming to significantly improve the Q value and extremely narrow resonant linewidth. Although the Q-BIC strategy can improve the Q value, its Q factor is inversely proportional to the symmetry perturbation parameter, making it highly sensitive to structural deviations or environmental disturbances. This inherent lack of robustness limits the practical application of high-Q chiral responses. To address the aforementioned challenges, the Brillouin zone folding effect offers an innovative approach to achieving high Q-chirality. By designing a mirror-symmetric broken metasurface structure to realize the Brillouin zone folding effect, it is expected to achieve a high Q-factor and tunable CD value, providing a novel device design solution to overcome the limitations of existing terahertz technology applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies, such as difficulty in integration and complex structure, and to provide an asymmetric coupled double-ring structure tunable terahertz circular dichroic device.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides an asymmetric coupled dual-ring structure tunable terahertz circular dichroism device, which is composed of several square column resonator unit structures arranged and spliced ​​periodically. Each unit structure includes a square substrate and a square column resonator disposed on the front side of the substrate. The square column resonator is a square column made of photosensitive silicon with a square cross-section. Its top surface is asymmetrically etched with a first annular cavity and a second annular cavity. The first and second annular cavities penetrate the height direction of the square column and extend to the substrate surface. Both retain unetched photosensitive silicon cylinders inside. The asymmetric coupled dual-ring structure tunable terahertz circular dichroism uses the contact surface between the square column resonator and air as the first and third ports, and the contact surface between the back side of the substrate and air as the second port.

[0006] Preferably, the first port is the input port of the terahertz wave, the second port is the transmission output port of the terahertz wave, and the third port is the reflection output port of the terahertz wave.

[0007] Preferably, the period of the unit structure PThe range is 110μm to 150μm.

[0008] Preferably, the cross-sectional side length of the square column resonator is... a The diameter is 70μm~80μm, the height is 95μm~102μm, the material is photosensitive silicon, and the conductivity of photosensitive silicon is 0~50 S / m.

[0009] Preferably, the substrate has a thickness of 25μm to 35μm, a side length of 110μm to 150μm, and is made of silicon dioxide.

[0010] Preferably, the substrate is made of silicon dioxide with a refractive index of 1.44.

[0011] Preferably, the inner and outer radii of the first and second annular cavities are the same, with the inner radius being... r 1. All are 2μm~5μm, outer radius r Both are 7μm~10μm.

[0012] Preferably, the first annular cavity and the second annular cavity are filled with air.

[0013] Preferably, the first and second annular cavities are eccentrically and asymmetrically arranged on the square top surface of the prismatic resonator. The distances from the center of the first top surface of the first annular cavity to a set of adjacent boundaries on the square top surface are 24~26μm and 36~38μm, respectively. The center of the second top surface of the second annular cavity is horizontally offset relative to the center of the first top surface. u 20μm~30μm, vertical offset v The range is 0μm to 18μm.

[0014] Preferably, in this device, the vertical offset of the center of the second top surface relative to the center of the first top surface of each unit structure is adjusted. v This allows for the control of the circular dichroism and quality factor of terahertz waves, as well as polarization conversion, resulting in two different operating modes. In the first operating mode, the terahertz wave is incident perpendicularly from the first port to the second port, achieving strong transmission of the LCP wave and low transmission of the RCP wave. In the second operating mode, the terahertz wave is incident perpendicularly from the first port to the third port, achieving low reflection of the LCP wave and high reflection of the RCP wave.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention designs an asymmetric coupled double-ring tunable terahertz circular dichroism device. Utilizing a combination of Brillouin zone folding mechanism and mirror symmetry breaking, the circular dichroism and quality factor of the terahertz wave, as well as polarization conversion, are controlled by changing the relative positions of the rings. The asymmetric coupled double-ring tunable terahertz circular dichroism device designed in this invention has a simple structure; simply changing the relative positions of the rings is sufficient to control the circular dichroism and quality factor, and achieve polarization conversion, making it suitable for future terahertz integrated systems. Attached Figure Description

[0016] Figure 1 A schematic diagram of the three-dimensional structure of the asymmetric coupled double-ring tunable terahertz circular dichroic metasurface; a schematic diagram of the three-dimensional structure (a), a side view of the unit structure (b), and a top view of the unit structure (c). Figure 2 The conductivity of photosensitive silicon σ Si =0S / m, u =24μm, v At a density of 14 μm, the designed structure exhibits the following scattering power decomposition diagrams in Cartesian coordinates at a frequency of 1.5752 THz: (a) and (b) x - y Magnetic field and displacement current distribution in the plane (b); Figure 3 The conductivity of photosensitive silicon σ Si =0S / m, u At a thickness of 24 μm, the designed structure was subjected to different offsets. v The following are the circular dichroism curves for transmission (a) and reflection (b); Figure 4 The conductivity of photosensitive silicon σ Si =0S / m, u =24μm, v When the diameter is 14μm, the LCP wave transmittance, RCP wave transmittance and transmission circular dichroism curves of the designed structure at the working frequency of 1.5752THz are shown in (a) and the LCP wave reflectance, RCP wave reflectance and reflection circular dichroism curves are shown in (b). Figure 5 The conductivity of photosensitive silicon σ Si =0S / m, u =24μm, v When the polarization angle of the circularly polarized wave varies from 0° to 90° at 14μm, the reflection circular dichroism spectrum (a) and transmission circular dichroism spectrum (b) of the designed structure are shown. Figure 6 The conductivity of photosensitive silicon σ Si =0S / m, u =24μm, v The reflection curve (a) and polarization conversion rate (b) of the designed structure at a =14μm. Figure 7 The figures (a) and (b) show the influence of the photosensitive silicon conductivity σSi on the transmission circular dichroism of the designed structure when the conductivity σSi varies between 0 S / m and 50 S / m, and u = 24 μm and v = 14 μm.

[0017] Figure 8 The conductivity of photosensitive silicon σ Si =0S / m, u When =24μm, v The quality factor changes of the circular dichroism curves of the designed structure in the first operating mode (a) and the second operating mode (b) as the diameter increases from 2 μm to 18 μm. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in the various embodiments of the present invention can be combined accordingly without mutual conflict.

[0019] For ease of description, the present invention defines... Figure 1 middle x The direction is the extension direction of the two identical annular aperture unit structures asymmetrically etched inside the resonator. z The direction is the thickness direction. y The direction is the width direction.

[0020] like Figure 1 As shown in Figure (a), in one embodiment of the present invention, an asymmetric coupled double-ring tunable terahertz circular dichroism device is provided. This device is composed of several square prism resonator unit structures, each containing two etched asymmetric circular rings, arranged and spliced ​​periodically. Each unit structure is identical and is periodically repeated on a plane to form the asymmetric coupled double-ring tunable terahertz circular dichroism device. Figure 1 (a) shows the configuration of 3×3 unit structures, but the specific number of unit structures to be spliced ​​needs to be set according to the actual device size and is not a limitation.

[0021] like Figure 1 As shown in Figures (b) and (c), each unit structure includes a square substrate 7 and a square column resonator 6 disposed on the front side of the substrate 7. The square column resonator 6 is made of photosensitive silicon and is a square column with a square cross-section. Its top surface is asymmetrically etched with a first annular cavity 4 and a second annular cavity 5. The first annular cavity 4 and the second annular cavity 5 extend through the height direction of the square column and reach the surface of the substrate 7. Both retain unetched photosensitive silicon cylinders inside. This asymmetric coupled double-ring structure with adjustable terahertz circular dichroism uses the contact surface between the top of the square column resonator 6 and the air (i.e., the top surface in the z-direction) as the first port 1 and the third port 3, and the contact surface between the back side of the substrate 7 and the air (i.e., the bottom surface in the z-direction) as the second port 2. Among them, the first port 1 is the input port of the terahertz wave, the second port 2 is the transmission output port of the terahertz wave, and the third port 3 is the reflection output port of the terahertz wave.

[0022] Additionally, it should be noted that the above-mentioned asymmetric coupled double-ring structure tunable terahertz circular dichroism device utilizes the Brillouin zone folding mechanism combined with mirror symmetry breaking. The relative positions of the first annular cavity 4 and the second annular cavity 5 on the square top surface of the square column resonator 6 create an eccentric asymmetric state that deviates from the center of the square top surface, thereby achieving the control of the circular dichroism and quality factor of the terahertz wave and realizing polarization conversion.

[0023] For ease of description, the center of the annular cavity 4 on the top surface of the unit structure is called the first top surface center, and the center of the annular cavity 5 on the top surface of the unit structure is called the second top surface center.

[0024] Furthermore, the specific selection and dimensional parameters of each structure of the aforementioned devices can be optimized according to actual performance requirements, with the final device performance meeting the usage needs as the standard. In the embodiments of the present invention, the structural parameters of the asymmetric coupled double-ring tunable terahertz circular dichroic device are optimized as follows: The period of the above unit structure P The side length of substrate 7 is 110μm to 150μm. The side length of the cross-section of the aforementioned rectangular prism resonator 6 is... a The thickness of the substrate 7 is 70μm~80μm, the height is 95μm~102μm, and the material is photosensitive silicon with a conductivity of 0~50 S / m. The thickness of the substrate 7 is 25μm~35μm, the side length is 110μm~150μm, and the material is silicon dioxide with a refractive index of 1.44. The inner and outer radii of the first annular cavity 4 and the second annular cavity 5 are the same, and the inner radius of both annular cavities is denoted as . r 1. The outer radius is denoted as . r2, then the inner radius r 1 is 2μm~5μm, outer radius r 2 is 7μm~10μm. The first annular cavity 4 and the second annular cavity 5 mentioned above are filled with air.

[0025] As mentioned above, the first annular cavity 4 and the second annular cavity 5 are eccentrically and asymmetrically arranged on the square top surface of the square column resonator 6. In the embodiment of the present invention, the specific asymmetry parameters are as follows: the distances from the center of the first top surface of the first annular cavity 4 to a set of adjacent boundaries in the square top surface are 24~26μm and 36~38μm, respectively; the horizontal offset of the center of the second top surface of the second annular cavity 5 relative to the center of the first top surface. u 20μm~30μm, vertical offset v The range is 0μm to 18μm.

[0026] See Figure 1 As shown in (c), the set of adjacent boundaries used to locate the center of the first top surface are the left and lower boundaries of the top surface of the square columnar resonator 6 in the figure. More preferably, the distance from the center of the first top surface of the first annular cavity 4 to the left boundary of the square top surface is 25.5 μm, and the distance from the center of the first top surface to the lower boundary of the square top surface is 37.5 μm. The horizontal offset of the center of the second top surface relative to the center of the first top surface... u 24μm, vertical offset v It can be adjusted between 0μm and 18μm according to actual needs.

[0027] Furthermore, this invention also provides a control method for the aforementioned asymmetric coupled dual-ring tunable terahertz circular dichroism device. This method can simultaneously control the circular dichroism response and quality factor of the device in both transmission and reflection modes, as well as achieve polarization conversion, and all these controls can be achieved synchronously at the same frequency. Specifically, in this device, the vertical offset of the center of the second top surface of each unit structure relative to the center of the first top surface can be controlled. v This allows for the control of the circular dichroism and quality factor of terahertz waves, as well as the realization of polarization conversion, resulting in two different operating modes.

[0028] In the first operating mode, when a terahertz wave is incident perpendicularly from the first port 1 to the second port 2, strong LCP wave transmission and low RCP wave transmission can be achieved. Therefore, this asymmetric coupled double-ring tunable terahertz circular dichroism device can achieve a transmission-tunable circular dichroism value of ±1 and a maximum of 5.36 × 10⁻⁶. 5 The quality factor.

[0029] In the second operating mode, terahertz waves incident perpendicularly from the first port 1 to the third port 3 can achieve low reflection of LCP waves and high reflection of RCP waves. Therefore, this asymmetric coupled double-ring structure tunable terahertz circular dichroism device can achieve a reflection-tunable circular dichroism value of -0.93 to 0.93 and a maximum of 4.99 × 10⁻⁶. 5 The quality factor and polarization conversion rate at a specific frequency point are 1.

[0030] Therefore, the present invention proposes an asymmetric coupled double-ring tunable terahertz circular dichroism structure, which utilizes the Brillouin zone folding mechanism and mirror symmetry breaking to exhibit terahertz circular dichroism modulation, Q factor enhancement, and polarization conversion functions that can be achieved without external bias, which is beneficial to the application and development of integrated devices.

[0031] The above-mentioned asymmetric coupled double-ring structure tunable terahertz circular dichroic device will be applied to a specific example to demonstrate its technical effect.

[0032] Example In this embodiment, the shapes of each component of the asymmetric coupled double-ring tunable terahertz circular dichroic device are as described above, see details below. Figure 1 Further details will not be elaborated here. The specific parameters of each component in this example are as follows: The period of the above unit structure P The cross-sectional side length of the aforementioned square columnar resonator 6 is 140 μm. a The thickness is 75 μm, the height is 100 μm, and the material is photosensitive silicon with a conductivity of 0~50 S / m. The substrate 7 has a thickness of 30 μm, a side length of 140 μm, and is made of silicon dioxide with a refractive index of 1.44. The inner and outer radii of the first annular cavity 4 and the second annular cavity 5 are identical, with the inner radius... r 1 is 4 μm, outer radius r 2 is 8 μm. The first annular cavity 4 and the second annular cavity 5 are filled with air. The distance from the center of the first top surface of the first annular cavity 4 to the left boundary of the square top surface is 25.5 μm, and the distance from the center of the first top surface to the lower boundary of the square top surface is 37.5 μm. The horizontal offset of the center of the second top surface of the second annular cavity 5 relative to the center of the first top surface is... u 24 μm, vertical offset v It can be adjusted between 0μm and 18μm according to actual needs.

[0033] This embodiment simulates the aforementioned asymmetric coupled double-ring tunable terahertz circular dichroism device based on the parameters described above, to demonstrate its technical effects. Theoretically, the differentiated responses of the material to left-handed (LCP) and right-handed (RCP) circularly polarized light lead to a chiral response in the device. By breaking the symmetry of the rings and causing the Brillouin zone of the unit cell to fold, terahertz circular dichroism modulation, Q-factor enhancement, and polarization conversion functions can be achieved. Figure 2 (a) shows that the electric quadrupole moment (EQ) scatters terahertz waves with greater power than the electric dipole moment (ED), magnetic dipole moment (MD), ring dipole (TD), and magnetic quadrupole moment (MQ). The electric quadrupole moment (EQ) scatters power, indicating that the tunable terahertz circular dichroism of this asymmetric coupled double-ring structure is mainly induced by the electric quadrupole moment (EQ). Figure 2 (b) shows that the magnetic field enhancement of the asymmetric coupled double-ring tunable terahertz circular dichroic device is located around the resonator, a phenomenon consistent with the characteristics of quasi-bound states excited by electric quadrupole moment (EQ). Therefore, the scattered power distribution diagram and magnetic field distribution diagram indicate that the designed asymmetric coupled double-ring tunable terahertz circular dichroic device is induced by electric quadrupole moment (EQ). Figure 3 (a) shows when v When =0, no circular dichroism peak appears, and so on. v As the number of peaks increases, circular dichroism begins to appear. v At 14µm, the transmission circular dichroism value reaches 1. Figure 3 (b) shows when v When =0, no circular dichroism peak appears, and so on. v As the number increases, a circular dichroism peak first appears, followed by a gradual widening of the linewidth. v At a focal length of 14µm, the circular dichroism value of the reflection reaches 0.93. This indicates that the device has strong circular polarization selectivity. Figure 4 When the circularly polarized wave shown in (a) is incident from the first port 1 and output from the second port 2, at a frequency of 1.5752 THz, the transmittance of the metasurface to the RCP wave is 0 and the transmittance to the LCP wave is 0.96, achieving a transmittance circular dichroism value of 1. Figure 4 (b) When the circularly polarized wave is incident from the first port 1 and output from the third port 3, at a frequency of 1.5752 THz, the device exhibits a reflectivity of 1 for the RCP wave and 0.04 for the LCP wave, achieving a circular dichroism value of 0.93. The results indicate that adjusting... v It can modulate the circular dichroism value and quality factor, in v =14μm, which can achieve the best terahertz circular dichroism effect. Figure 5 (a) and Figure 5 (b) shows a circularly polarized wave whose polarization angle varies from 0° to 90°, and whose CD value is at a frequency of 1.5752 THz.T Keep it at 1, CD R The value was kept at 0.93, indicating that the structure is robust to the polarization angles of left-hand and right-hand circularly polarized waves. Figure 6 (a) shows the incident frequency of the LCP wave at 1.5752 THz, r RL The amplitude is 0.2, r LL With an amplitude of 0.02, when RCP is incident, r LR Amplitude is 1, r RR The amplitude is 0.02, which indicates that under the incident circularly polarized terahertz wave, the reflected wave is mainly composed of cross-polarized waves, allowing LCP to be converted into RCP, and also allowing RCP to be converted into LCP. Figure 6 In the reflection mode shown in (b), the polarization conversion rates of both LCP and RCP are 1 at 1.5752 THz. The results show that the device can achieve highly efficient polarization control of LCP and RCP waves at a specific frequency (1.5752 THz). Figure 7 (a) shows that the conductivity of photosensitive silicon varies between 0 S / m and 50 S / m, the position of the resonance peak of the transmission CD peak remains unchanged, the CD peak value gradually decreases from 1 to 0, and the modulation depth (CDmax-CDmin) / CDmax is 100%. Figure 7 (b) shows that the reflection CD value gradually decreases from 0.93 to 0, the resonant linewidth gradually widens, and the modulation depth is 100%. The results indicate that changing the conductivity of photosensitive silicon can modulate the circular dichroism and Q factor of the device. Figure 8 (a) v As the aperture size changes from 2 μm to 18 μm, the quality factor Q of the transmission CD curve increases from 5.36 × 10⁻⁶. 5 It gradually decreased to 1.99×10 3 . Figure 8 (b) v As the reflectance CD curve changes from 2 μm to 18 μm, the quality factor Q increases from 4.99 × 10⁻⁶. 5 It gradually decreased to 1.06×10 3 The results show that the device in this embodiment has been modified. v The value of the Q factor can be adjusted.

[0034] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. An asymmetrically coupled double-ring structure tunable terahertz circular dichroism device, characterized in that, A plurality of square column resonator unit structures are arranged periodically and spliced together; each unit structure comprises a square substrate (7) and a square column resonator (6) arranged on the front surface of the substrate (7); the square column resonator (6) is made of photosensitive silicon material and has a square cross section, and the top surface of the square column resonator (6) is asymmetrically etched with a first circular ring cavity (4) and a second circular ring cavity (5), the first circular ring cavity (4) and the second circular ring cavity (5) penetrate the height direction of the square column and extend to the surface of the substrate (7), and the interiors of the two cavities each remain a photosensitive silicon cylinder which is not etched; the asymmetrically coupled double-ring structure adjustable terahertz circular dichroism takes the contact surface between the square column resonator (6) and air as a first port (1) and a third port (3), and takes the contact surface between the back surface of the substrate (7) and air as a second port (2). 2.The asymmetrically coupled split-ring resonator tunable terahertz circular dichroism device according to claim 1, wherein, The first port (1) is an input port of terahertz waves, the second port (2) is a transmission output port of terahertz waves, and the third port (3) is a reflection output port of terahertz waves. 3.The asymmetrically coupled split-ring resonator tunable terahertz circular dichroism device according to claim 1, wherein, The period of the unit structure is 110-150 μm.

4. The device according to claim 1, wherein, The square column resonator (6) has a cross-sectional side length of 70-80 μm, a height of 95-102 μm, and is made of photosensitive silicon, and the photosensitive silicon has an electrical conductivity of 0-50 S / m.

5. The device according to claim 1, wherein, The substrate (7) has a thickness of 25-35 μm, a side length of 110-150 μm, and is made of silicon dioxide.

6. The device according to claim 1, wherein, The refractive index of the silicon dioxide of the substrate (7) is 1.

44.

7. The device according to claim 1, wherein, The inner and outer radii of the first circular ring cavity (4) and the second circular ring cavity (5) are uniform, the inner radius is 2-5 μm, and the outer radius is 7-10 μm. 8.The asymmetrically coupled split-ring resonator tunable terahertz circular dichroism device of claim 1, wherein, The first circular ring cavity (4) and the second circular ring cavity (5) are filled with air.

9. The device according to claim 1, wherein, The first circular ring cavity (4) and the second circular ring cavity (5) are eccentrically and asymmetrically arranged on the square top surface of the square column resonator (6), the distance from the first top center of the first circular ring cavity (4) to a group of adjacent boundaries of the square top surface is 24-26 μm and 36-38 μm respectively, the horizontal offset of the second top center of the second circular ring cavity (5) relative to the first top center is 20-30 μm, and the vertical offset is 0-18 μm.

10. The device according to claim 1, wherein, In the device, the vertical offset of the second top center of each unit structure relative to the first top center is adjusted to adjust the circular dichroism and the quality factor of terahertz waves and to realize polarization conversion, forming two different working modes; in the first working mode, the terahertz wave is vertically incident from the first port (1) to the second port (2), realizing strong transmission of LCP wave and low transmission of RCP wave; in the second working mode, the terahertz wave is vertically incident from the first port (1) to the third port (3), realizing low reflection of LCP wave and high reflection of RCP wave.

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