Dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating

Abstract

The application discloses a dynamic terahertz beam deflector of a metal metasurface-liquid crystal-metal grating structure. The device comprises a first dielectric substrate layer, a metal metasurface layer, a liquid crystal layer, a metal grating layer and a second dielectric substrate layer. By composing a tunable photonic resonant cavity with the metal metasurface layer, the liquid crystal layer and the metal grating layer, enhanced in-cavity polarization mode conversion and dynamically controlled terahertz beam deflection can be realized. By changing the frequency of the incident light, the deflection angle of the outgoing light beam is scanned by 37.5-50°. When the frequency of the incident light is 0.69 THz and the deflection angle is 47.5°, a diffraction intensity of 50% and a high-intensity modulation depth of 99.6% are realized. The device has the advantages of flexible design, easy processing, low price, large modulation range and the like, and is conducive to integration and miniaturization. Therefore, the device can be used in terahertz spectrum, imaging, radar and communication systems and the like.

Description

Technical Field

[0001] This invention belongs to the field of terahertz application technology, specifically relating to a dynamic terahertz beam deflector with a metal metasurface-liquid crystal-metal grating structure. Background Technology

[0002] Terahertz (THz, 1 THz = 10 12 THz waves are generally defined as electromagnetic waves with oscillation frequencies ranging from 0.1 to 10 THz, and wavelengths ranging from 3 mm to 30 μm, representing a transitional region between macroscopic electronics and microscopic photonics. THz radiation has attracted widespread attention due to its unique fingerprint spectrum, high penetration, low photon energy, and broadband characteristics. THz technology has broad applications in imaging, non-destructive testing, biomedicine, and wireless communication. With the rapid development of high-performance, high-sensitivity THz sources and detectors, THz waves and related technologies have also made rapid progress. Their practical applications rely heavily on the support of high-performance THz functional devices, such as modulators, waveguides, filters, isolators, polarizers, phase shifters, and wavefront modulation devices.

[0003] Among them, THz beam steering can control the beam direction in the transmission or reflection half-space [Nat. Photon., 2015, 9(11):717-720], thereby realizing the directional transmission of the beam, which is one of the key functional devices in the fields of radar and communication. In particular, dynamic THz beam steering devices are even more important for practical applications [Light: Sci. Appl., 2018, 7(1):28], which can flexibly control the direction or intensity of the beam. Traditional beam control mechanical manipulation methods, including mechanical scanning [IEEE Trans. Terah. Sci. & Tech., 2019, 9(1):47-54], phased array [IEEE J. Solid-State Circuits, 2015, 50(2):597-609], and frequency scanning antennas [J. Lightw. Technol., 2021, 39(17):5502-5507], often suffer from drawbacks such as slow response speed, small adjustment range, and difficult adjustment methods, which hinder their development and application in the THz band.

[0004] In recent years, metasurfaces, as a novel type of subwavelength artificial microstructure, have been developed with advantages such as flexible design, simple manufacturing, ultra-thin dimensions, and easy integration. More importantly, artificially designed metasurfaces provide unprecedented degrees of freedom for manipulating the amplitude, phase, polarization, and orbital angular momentum of THz waves [Light: Advanced Manufacturing, 2021, 2:10], and can be used for polarization conversion, spatial light modulation, holographic imaging, Bessel beam and vortex beam generation, etc. In addition, metasurfaces with linear phase gradients can flexibly manipulate the wavefront of outgoing waves [Nano Lett., 2012, 12(12):6223-6229], thereby realizing beam steering and wavefront shaping.

[0005] To achieve dynamic control of THz beam steering, some reported feasible methods involve integrating tunable functional materials and components onto metasurfaces [Light: Advanced Manufacturing, 2021, 2:10], such as microelectromechanical system-based actuators, optically pumped semiconductor materials (silicon and GaAs), phase change materials (VO2 and GST), two-dimensional materials (graphene), liquid crystal (LC) materials, and magneto-optical materials (InSb). All of these methods can achieve relatively good dynamic optical responses through electrical, optical, and thermal excitation, and each method has its own advantages and disadvantages.

[0006] Liquid crystals, as a functional material, not only possess broadband optical anisotropy but can also be flexibly modulated by external fields such as heat, light, electric fields, and magnetic fields. Recently, various dynamic THz liquid crystal devices, such as tunable absorbers, modulators, phase shifters, and waveplates, have been proposed and studied. The tunable anisotropy of liquid crystals also provides new opportunities for the dynamic manipulation of THz waves. However, compared with optical and near-infrared wavelengths, due to the long wave length of THz waves and the limited birefringence of liquid crystals, the size of THz liquid crystal devices needs to be on the order of millimeters to achieve a sufficiently large phase shift or modulation range (π / 2 or π phase delay), which is not conducive to integration and miniaturization [Opt. Mater. Express, 2016, 6(7):2283-2290]. The integration of liquid crystals with metasurfaces provides a feasible solution to these problems. This composite device can utilize the resonant modes of metasurfaces and the tunable anisotropy of liquid crystals to enhance the phase shift of THz waves. Recently, researchers have proposed a dynamic beam control device based on a liquid crystal integrated coded metasurface. This device can control the propagation of electromagnetic waves in the reflecting half-space [Appl. Phys. Lett., 2020, 116(13):131104] and the transmitting half-space [Adv. Opt. Mater., 2021, 9(22):2100932] using a simple design procedure to achieve response phases of 0° and 180° (i.e., “0” and “1”). Building upon previous research, how to achieve a dynamic beam steering device with high diffraction efficiency, wide scanning angle, and high modulation depth remains a problem worthy of further investigation.

[0007] In summary, on the one hand, the development of terahertz application systems urgently requires high-performance active terahertz beam control devices; on the other hand, the active terahertz beam control devices reported at home and abroad still have shortcomings in terms of diffraction efficiency, scanning angle, modulation depth, and control methods. New control mechanisms and methods need to be introduced to further improve the performance of the devices in order to meet the actual needs of application systems. Summary of the Invention

[0008] The purpose of this invention is to provide a dynamic terahertz beam deflector with a metal metasurface-liquid crystal-metal grating structure. The metal metasurface and metal grating form a photonic resonant cavity, enabling polarization mode conversion of incident linearly polarized terahertz waves. Furthermore, the dielectric anisotropy and dynamic tunability of the liquid crystal enhance and dynamically control the polarization mode conversion within the cavity. In addition, the metal metasurface is composed of a series of open resonant rings periodically arranged in the xy two-dimensional plane. Each supercell contains six open resonant rings of different geometric dimensions. The phase difference between any two adjacent open resonant rings is π / 3, and the phase difference between each supercell is 2π. Ultimately, this device can achieve dynamic terahertz beam deflection and intensity modulation by changing the direction of the magnetic field.

[0009] The technical solution of this invention is as follows:

[0010] A dynamic terahertz beam deflector with a metal metasurface-liquid crystal-metal grating structure is disclosed. The dynamic terahertz beam deflector comprises a first dielectric substrate, a metal metasurface layer, a liquid crystal layer, a metal grating layer, and a second dielectric substrate layer arranged sequentially. The metal metasurface layer consists of six different open-ended resonant rings arranged periodically to provide orthogonal polarization conversion and spatial gradient phase distribution, thereby deflecting the incident linearly polarized terahertz beam. The metal metasurface layer is deposited on the back side of the first dielectric substrate. The metal grating layer consists of periodically spaced metal gratings and is deposited on the front side of the second dielectric substrate. The liquid crystal layer consists of anisotropic liquid crystal molecules to enhance deflection conversion efficiency and dynamically control polarization mode conversion within the cavity.

[0011] Preferably, the first dielectric substrate layer and the second dielectric substrate layer are undoped fused silica optical glass with a thickness of 300-500 μm.

[0012] Preferably, the thickness of the metal grating layer is 200 nm.

[0013] Preferably, the thickness and linewidth of the metal grid strip are 10-20 μm, and the period is 20-40 μm.

[0014] Preferably, the thickness of the metal metasurface layer is 200 nm.

[0015] Preferably, the metal metasurface layer is composed of a series of open resonant rings arranged periodically in the xy two-dimensional plane, and six open resonant rings with different geometric dimensions form a supercell. By optimizing the inner radius r1, outer radius r2, opening angle α, and the angle β between the axis of symmetry and the x-axis of the six open resonant rings, the phase difference between two adjacent open resonant rings is π / 3, and the phase difference between each supercell is 2π.

[0016] Preferably, the six open resonant rings with different geometric dimensions in the metal metasurface layer are arranged in a direction parallel to the direction of the metal grating strips in the metal grating layer.

[0017] Preferably, the thickness of the liquid crystal layer is 240–260 μm.

[0018] Preferably, the liquid crystal layer uses a large birefringence nematic liquid crystal as the liquid crystal material, and its birefringence coefficient in the terahertz band is 0.28 to 0.32.

[0019] Preferably, the method of using the dynamic terahertz beam deflector is as follows: the dynamic terahertz beam deflector is placed at the center of the variable slide rail in the terahertz optical path, and a variable external magnetic field is applied in a plane perpendicular to the propagation direction. A polarizer P1 is placed before the dynamic terahertz beam deflector so that the polarization direction of the incident linearly polarized light is fixed in the direction of the metal grating (i.e., the x-axis). Another polarizer P2 and a detector are placed after the dynamic terahertz beam deflector. Both the polarizer and the detector are placed on the rotating arm of the variable slide rail. The detection of orthogonally polarized diffracted light (i.e., y-polarized light) at different exit angles is achieved by rotating the rotating arm of the variable slide rail. The center frequency of the diffracted light at different exit angles satisfies Snell's law. When the incident wave is x-polarized light with a frequency in the range of 0.65 to 0.82 THz, the exit y-polarized light after passing through the device undergoes a deflection angle scan of 37.5 to 50°. By changing the magnitude and direction of the variable external magnetic field, the intensity of the diffracted light changes at different exit angles: when a magnetic field is applied along the x-axis, the outgoing beam is mainly concentrated in the +1st order diffraction direction due to constructive interference between the conversion modes within the cavity; when a magnetic field is applied along the y-axis or z-axis, the intensity of the outgoing light is significantly reduced due to destructive interference between the conversion modes within the cavity, thereby realizing dynamic terahertz polarization conversion and beam deflection driven by magnetic fields in different directions.

[0020] The beneficial effects and advantages of this invention are:

[0021] 1. The metal metasurface layer in this invention is composed of a series of open resonant rings arranged periodically in the xy two-dimensional plane. Each supercell contains six open resonant rings with different geometric dimensions. By optimizing the inner radius r1, outer radius r2, opening angle α, and the angle β between the axis of symmetry and the x-axis of the open resonant rings in the supercell, the phase difference between two adjacent open resonant rings is π / 3, and the phase difference between each supercell is 2π. This enables the device to undergo polarization conversion and beam deflection in the range of 0.65 to 0.82 THz, achieving a maximum scanning angle range of 37.5 to 50°.

[0022] 2. This invention constructs a photonic resonant cavity using a metal metasurface layer and a metal grating layer to achieve polarization mode conversion of incident linearly polarized light. Furthermore, it utilizes multiple reflections of terahertz waves within the cavity to enhance the efficiency of polarization mode conversion. Additionally, the introduction of a uniaxial anisotropic dielectric liquid crystal material within the resonant cavity further improves the polarization conversion efficiency of the cavity modes. These two enhancement mechanisms work together to improve the overall diffraction efficiency of the device, ultimately achieving a maximum diffraction intensity of 50% at 0.69 THz.

[0023] 3. This device ingeniously utilizes the dielectric tunable properties of the liquid crystal in the resonant cavity to dynamically control the coherent matching conditions between multiple reflected beams, thereby achieving active modulation of the intensity value of the diffracted beam. It can achieve a maximum modulation depth of 99.6% at 0.69THz. This dynamic control characteristic and high modulation depth greatly improve the practicality of the device and meet the requirements of dynamic terahertz beam deflectors.

[0024] 4. Electron beam lithography and lift-off techniques are used to prepare metal metasurfaces and metal gratings. The preparation process is simple and reliable. The metal metasurfaces, metal gratings and liquid crystals are prepared by encapsulating them with UV adhesive. The materials used are inexpensive and suitable for large-scale, low-cost production. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the dynamic terahertz beam deflector with a metal metasurface-liquid crystal-metal grating structure in the experimental system.

[0026] Figure 2 This is a top view of the dynamic terahertz beam deflector with a metal metasurface-liquid crystal-metal grating structure in the experimental system.

[0027] Figure 3 These are optical microscope images of metal gratings, metal metasurfaces, and the scale of an open resonant ring in a metal metasurface;

[0028] Figure 4 (a) and 4(d) are experimental intensity spectrum diagrams obtained at different emission angles when a magnetic field is applied along the x-axis.

[0029] Figure 4 (b) and 4(e) are experimental intensity spectrum diagrams obtained at different emission angles when a magnetic field is applied along the y-axis.

[0030] Figure 4 (c) and 4(f) are experimental intensity spectrum diagrams obtained at different exit angles when a magnetic field is applied along the z-axis.

[0031] Figure 5 (a) is the simulated E-field distribution of the device at a frequency of 0.72 THz when the magnetic field is along the x-axis, y-axis and z-axis;

[0032] Figure 5 (b) is the experimental intensity spectrum of the device at a diffraction angle of 47.5° when the magnetic field is along the x-axis, y-axis and z-axis;

[0033] Figure 5 (c) Simulated angular intensity distribution of the device at a frequency of 0.72 THz and experimental angular intensity distribution of the device at a frequency of 0.69 THz when the magnetic field is along the x-axis, y-axis and z-axis;

[0034] Figure 6 (a) is the experimental intensity spectrum of the device as a function of the magnetic field at a diffraction angle of 47.5°;

[0035] Figure 6 (b) is the diffraction intensity modulation curve at the 0.69 THz frequency position of the device;

[0036] In the figure: 1. First dielectric substrate layer; 2. Metal metasurface layer; 3. Liquid crystal layer; 4. Metal grating layer; 5. Second dielectric substrate layer; 6. Open resonant ring; 7. Liquid crystal molecule; 8. Metal grating; 9. Polarizer P1; 10. Polarizer P2; 11. Detector. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0038] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Example

[0039] Figure 1 and Figure 2 A schematic diagram of a dynamic terahertz beam deflector structure is shown. A 200 nm thick metal film is deposited on the surface of a 300 μm thick first dielectric substrate 1 and a second dielectric substrate 5. Subsequently, metal metasurface 2 and metal grating layer 4 structures are fabricated on the first dielectric substrate 1 and the second dielectric substrate 5, respectively, using electron beam lithography and lift-off techniques.

[0040] The prepared metal metasurface 2 and metal grating layer 4 were encapsulated by UV curing to form a 250 μm thick photonic resonant cavity. A layer of tunable liquid crystal material was filled in the resonant cavity. The liquid crystal used in this work is a high birefringence nematic liquid crystal with a birefringence coefficient of 0.28 to 0.32 in the terahertz band.

[0041] In this design, the linewidth and period in the x-direction of the metal grating layer 4 are 10 μm and 20 μm, respectively. The metal metasurface 2 is composed of six different open-ended resonant rings 6 arranged periodically. By changing the geometric parameters of the open-ended resonant rings 6 (including the inner radius r1, outer radius r2, opening angle α, and the angle β between the axis of symmetry and the x-axis), we can flexibly control the amplitude and phase of the output wave. Here, we selected six different open-ended resonant rings 6 to form a supercell with essentially the same amplitude, and the phase difference between any two adjacent open-ended resonant rings 6 is π / 3. The periods of the supercell in the x and y directions are P, respectively. x =600μm and P y =100μm.

[0042] Figure 3 Optical micrographs of the metal grating layer 4 and the metal metasurface 2 are given, along with the geometric dimensions of the six open resonant rings 6 in the metal metasurface 2.

[0043] Next, the device was measured using an angle-resolved terahertz time-domain spectroscopy system built in the laboratory. The polarizer before the sample was fixed on the x-axis, making the incident terahertz wave x-polarized. The polarizer after the sample was rotated to the y-axis, and the y-polarized output wave at different angles was detected by a robotic arm on a rotating variable slide rail. Figure 4 The figure shows the experimental intensity spectrum at different emission angles. It can be seen from the figure that the spectral signal at a specific emission angle exhibits narrowband characteristics, and the center frequency and diffraction angle of the spectral signal conform to Snell's law.

[0044] When a magnetic field along the x-axis is applied to the device (i.e., the optical axis of the liquid crystal molecules points to the x-axis), the center frequency of the output wave gradually decreases as the diffraction angle increases, and the +1st order diffraction dominates in the output wave, meaning a strong output signal appears in the positive angle diffraction intensity spectrum, such as... Figure 4 As shown in (a); the diffraction intensity spectrum at negative angles (i.e., -1st order) is essentially 0, as... Figure 4 As shown in (d). Therefore, by changing the frequency of the incident light (0.65–0.82 THz), output light emitted at different angles can be achieved, with a maximum scanning angle range of 37.5–50°. When a magnetic field along the y-axis or z-axis is applied, the +1st order diffraction still dominates in the output wave, while the -1st order diffraction is almost zero, as shown in (d). Figure 4 As shown in (b), 4(c), 4(e), and 4(f), the diffraction intensity spectrum with a magnetic field applied along the y-axis or z-axis is significantly different from that with a magnetic field applied along the x-axis. This indicates that the orientation of the optical axis of the liquid crystal molecules can change the resonance matching condition of the intracavity mode conversion, thereby dynamically modulating the intensity of the diffracted light.

[0045] like Figure 5(a) shows the simulated E-field distribution of the device at a frequency of 0.72 THz under different liquid crystal molecule orientations. When the liquid crystal molecules are pointing in the x-direction (defined as the ON state), due to constructive interference of the cavity modes, a beam deflection of 44° can be observed. This deflection angle corresponds to the +1st order diffraction angle at this frequency. When the liquid crystal molecules are pointing in the y-direction (or z-direction), due to destructive interference of the cavity modes, there is no output wave. This situation is defined as the OFF state. This dynamic modulation characteristic of the diffracted light intensity has also been verified experimentally, such as... Figure 5 As shown in (b), by changing the direction of the applied magnetic field, the orientation of the liquid crystal molecules is dynamically controlled, thereby altering the resonance matching condition for intracavity mode switching and achieving dynamic modulation of the diffraction intensity at a 47.5° diffraction angle. Further, intensity spectrum diagrams of the device at ±47.5° diffraction angles are given under different magnetic field directions: When in the ON state, the +1st order diffraction intensity (corresponding to a 47.5° diffraction angle) at the 0.69THz frequency position reaches 50%, while the -1st order diffraction intensity (corresponding to a -47.5° diffraction angle) is only 5%. When a magnetic field is applied along the y-axis or z-axis, both the +1st order (corresponding to a 47.5° diffraction angle) and -1st order (corresponding to a 47.5° diffraction angle) diffraction intensities are below 3%, indicating that the device is in the OFF state. Furthermore, to compare the simulation and experimental results, the angular intensity distribution of the output wave in the simulation (0.72THz) and experiment (0.69THz) are plotted, as shown below. Figure 5 As shown in (c), both simulation and experimental results demonstrate that the device can convert a beam of linearly polarized light into orthogonally linearly polarized light, and that the output light is mainly deflected to the +1 order in the ON state, while the output light is almost zero in the OFF state, thus achieving dynamic modulation of the diffraction intensity. The simulation results agree well with the experimental results, except for a slight difference in the operating frequency, which is mainly due to errors in sample preparation and approximations in the simulation.

[0046] Finally, to analyze the intensity modulation characteristics of the device, the orientation of the optical axis of the liquid crystal molecules was dynamically manipulated by adjusting the magnitude of the magnetic fields in two directions (i.e., the x-axis and the y-axis). This resulted in the observation of a gradual decrease in the intensity of a narrowband signal with a center frequency around 0.69 THz at a diffraction angle of 47.5°. Figure 6 As shown in (a). This diffraction intensity modulation characteristic can also be expressed using ΔI / I max =(I max -I min ) / I max To describe, such as Figure 6 As shown in (b), the diffraction intensity modulation depth of the device can reach 99.6%.

[0047] Compared to previous terahertz beam steering devices, this invention, on the one hand, effectively enhances the intracavity mode conversion efficiency by combining a metal metasurface 2 and a metal grating layer 4 into a photonic resonant cavity; on the other hand, the introduction of a tunable liquid crystal material within the cavity further enhances the intracavity mode conversion efficiency and allows for the control of the resonant matching conditions of the intracavity modes, thus enabling dynamic control of THz beam deflection. This device can achieve polarization conversion and beam deflection in the range of 0.65–0.82 THz, with a maximum scanning angle range of 37.5–50°; and, with an incident light frequency of 0.69 THz and a deflection angle of 47.5°, it achieves 50% diffraction intensity and 99.6% high-intensity modulation depth. The metal metasurface and metal grating structure used have advantages such as flexible design, large adjustable range, and mature fabrication process; the liquid crystal material used has low loss, low cost and flexible external field modulation characteristics in the THz band; the liquid crystal is encapsulated in the photonic resonant cavity composed of metal metasurface 2 and metal grating layer 4 using ultraviolet glue, which improves the conversion efficiency and modulation depth of the device, while also increasing the stability of the device.

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A dynamic terahertz beam deflector based on a metal metasurface-liquid crystal-metal grating, characterized in that, The dynamic terahertz beam deflector includes a first dielectric substrate layer (1), a metal metasurface layer (2), a liquid crystal layer (3), a metal grating layer (4), and a second dielectric substrate layer (5) arranged sequentially. The metal metasurface layer (2) is composed of six different open resonant rings (6) arranged in a periodic manner, and the metal metasurface layer (2) is deposited on the back side of the first dielectric substrate layer (1). The metal grating layer (4) is composed of periodically spaced metal grating strips (8), and the metal grating layer (4) is deposited on the front side of the second dielectric substrate layer (5). The liquid crystal layer (3) is composed of anisotropic liquid crystal molecules (7). The metal metasurface layer (2) is composed of a series of open resonant rings arranged periodically in the xy two-dimensional plane, and six open resonant rings (6) with different geometric dimensions form a supercell. By optimizing the inner radius r1, outer radius r2, opening angle α and the angle β between the axis of symmetry and the x-axis of the six open resonant rings (6), the phase difference between two adjacent open resonant rings (6) is π / 3, and the phase difference between each supercell is 2π.

2. The dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The first dielectric substrate layer (1) and the second dielectric substrate layer (5) are undoped fused silica optical glass with a thickness of 300-500 μm.

3. The dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The thickness of the metal grating layer (4) is 200 nm.

4. The dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The thickness and linewidth of the metal grid (8) are 10-20 μm, and the period is 20-40 μm.

5. The dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The thickness of the metal metasurface layer (2) is 200 nm.

6. The dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The six open resonant rings (6) with different geometric dimensions in the metal metasurface layer (2) are arranged in a direction parallel to the direction of the metal grating strips (8) in the metal grating layer (4).

7. The dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The thickness of the liquid crystal layer (3) is 240-260 μm.

8. The dynamic terahertz beam deflector of metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The liquid crystal layer (3) uses a large birefringence nematic liquid crystal as the liquid crystal material, and its birefringence coefficient in the terahertz band is 0.28 to 0.

32.

9. The dynamic terahertz beam deflector of the metal metasurface-liquid crystal-metal grating according to claim 1, characterized in that, The method of using the dynamic terahertz beam deflector is as follows: the dynamic terahertz beam deflector is placed at the center of the variable slide rail in the terahertz optical path, and a variable external magnetic field is applied in the plane perpendicular to the propagation direction. A polarizer P1 (9) is placed in front of the dynamic terahertz beam deflector so that the polarization direction of the incident linear polarized light is fixed in the direction of the metal grid (8). Another polarizer P2 (10) and a detector (11) are placed after the dynamic terahertz beam deflector. The polarizer P2 (10) and the detector (11) are both placed on the rotating arm of the variable slide rail. The detection of orthogonally polarized diffracted light with different exit angle directions is achieved by rotating the rotating arm of the variable slide rail.

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