A dynamically regulated nonvolatile broadband terahertz dual-channel vortex magneto-optical cascade superstructure device

Abstract

The application discloses a kind of dynamically regulated non-volatile broadband terahertz double-channel vortex magneto-optical cascade superstructure devices, belong to the technical field of terahertz devices.The device is composed of structured metal layer, magneto-optical material layer.Structured metal layer is used to construct near field and far field two channel vortex, and magneto-optical material layer plays the role of deflecting incident ray bias angle and maintaining the stability of regulation state.The whole device dynamically regulates the intensity and polarization state distribution rotation of plasmonic vortex and free space vortex by applying external magnetic field.The working frequency band of the device is located at 0.4-0.72Hz, and the vortex mode purity can reach up to 98%, and the maximum range of vortex field distribution rotation is 90°.This magneto-optical cascade superstructure device has the advantages of broadband excitation, near-far field multiplexing and dynamic adjustment, and has important application value in the fields of terahertz high-capacity communication, non-volatile storage and information processing.

Description

Technical Field

[0001] This invention belongs to the field of terahertz application technology, specifically relating to a dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure device. Background Technology

[0002] Terahertz waves are electromagnetic waves located between microwaves and infrared waves, with a frequency range of 0.1-10 THz. With the development of terahertz technology, terahertz functional devices have broad application prospects in high-capacity communication, biochemical sensing, information processing, and particle manipulation. Vortex light is a special type of beam carrying orbital angular momentum; the orthogonality between different modes of vortex fields effectively improves the channel capacity of communication networks. Free-space vortices and surface plasmon vortices are light field distributions excited by two different electromagnetic wave propagation modes, capable of operating in near-field and far-field channels, respectively. However, most currently reported vortex devices suffer from single operating modes, narrow response bandwidth, complex structures, and fixed functions. Therefore, developing integrated multi-channel broadband dynamically tunable vortex devices is crucial for achieving miniaturization, high integration, and multi-scenario applications in terahertz communication systems.

[0003] Traditional vortex generating devices mostly employ methods such as spiral phase plates and spatial light modulators. The large size and bulkiness of these optical components make miniaturization and integration difficult in practical applications. Metasurfaces, an array of artificial microstructures, can manipulate the amplitude, phase, and polarization state of incident light at the subwavelength scale, making them an excellent candidate for realizing miniaturized integrated systems. Currently, researchers have used various methods based on metasurface platforms to achieve the generation, manipulation, and detection of vortex beams. For example, Zang et al. achieved on-chip multi-mode plasma vortex design through orthogonal slits based on a joint control mechanism of geometric phase and dynamic phase, with the vortex mode determined by the chiral state of the incident excitation wave [Advanced Optical Materials 2018, 7(3): 1801328]; Jiang et al. utilized the characteristic that slit rectangular apertures can simultaneously excite plasma waves and scatter free transmitted waves, and achieved the simultaneous generation of on-chip plasma vortices and free-space vortices by locally controlling the rotation angle of the rectangular aperture units etched on the metal thin film [Photonics Research 2020, 8(6): 986-994]. However, most of the above devices are limited to a single working channel, and their simple construction results in a narrow working bandwidth. In addition, the fixed structure also makes it difficult for the devices themselves to adapt to complex and diverse working scenarios.

[0004] In summary, on the one hand, designing and implementing integrable multi-channel vortex devices is of great significance for promoting the expansion of terahertz communication systems, high-dimensional information processing, and multifunctional particle manipulation. On the other hand, most currently reported vortex devices rely on a single building block, making it difficult to support a wide operating range, and they generally lack dynamic tuning capabilities, thus limiting their application scenarios. Therefore, developing a terahertz vortex device with multiple operating channels, a wide operating bandwidth, and dynamically adjustable functions is particularly important for the development of terahertz communication systems. Summary of the Invention

[0005] The purpose of this invention is to provide a dynamically adjustable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure device to solve a series of key technical problems in the background art, such as limited working channels, narrow working bandwidth, and lack of dynamic control schemes in vortex generators.

[0006] The technical solution of this invention is as follows: A dynamically controllable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device consists of a structured metal layer and a magneto-optical material layer. The structured metal layer is composed of pairs of rectangular holes arranged in inner and outer rings on a metal thin film. The number of rectangular hole pairs in each ring substructure is the same, while the sizes of the rectangular holes on the inner and outer rings are different. This ensures that the inner and outer ring substructures excite surface plasma waves with different resonant frequencies, which propagate to the center of the device structure to generate a superimposed interference field distribution with a broadband response. The magneto-optical material layer is a thin film structure made of hexagonal ferrite ceramic material. Its inherent ferromagnetic properties enable it to effectively maintain its magnetized state after the external excitation disappears, achieving non-volatile state control. Simultaneously, its Faraday magneto-optical effect deflects the incident beam angle. By applying a magnetic field within the range of -0.67 T to 0.67 T to the magneto-optical material layer, the incident beam angle is dynamically deflected, thereby achieving rotational control of the outgoing vortex field distribution.

[0007] The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device comprises a structured metal layer (1) and a magneto-optical material layer (2). The structured metal layer (1) is prepared by ion sputtering and has a thickness of [missing information]. h The rectangular holes (7) and (8) are formed by laser direct writing on a metal thin film of approximately 100-200 nm. The long side of the rectangular holes ranges from 160 μm to 270 μm, and the short side is 50 μm. The rectangular holes with different aspect ratios correspond to different excitation resonant frequencies, thereby realizing a broadband response of the on-chip interference field. The rectangular hole pair (5) is composed of a pair of mutually orthogonal rectangular holes (7). The initial orientation angles of the two rectangular holes are respectively β 1 =45°, β 2=135°, the initial lateral distance between the geometric centers is 3 / 4 of the surface plasma wavelength, and the longitudinal distance is 0; the rectangular aperture pair (6) is composed of a pair of mutually orthogonal rectangular apertures (8), and the initial orientation angles of the two rectangular apertures are respectively β 3 =135° β 4 =45°, the initial lateral distance between the geometric centers is 3 / 4 of the surface plasma wavelength, and the longitudinal distance is 0; the distance between the rectangular hole pair (5) and the rectangular hole pair (6) is L. The ring substructure (3) is formed by uniformly arranging the rectangular hole pairs (5) at any angular interval of 6° to 25° on a radius of 45°. r 1 On the inner ring, the rectangular hole at each position is relative to x The rotation angle of the axis is the initial orientation angle. β Including the spatial azimuth angle; the ring substructure (4) is composed of rectangular holes (6) evenly arranged at any value within the angular interval of 6°~25° on a radius of r 2 On the outer ring, the rectangular hole at each position is relative to x The rotation angle of the axis is the initial orientation angle β plus the spatial azimuth angle. This rotational structure configuration allows the geometric phase excited by the rectangular aperture structure to satisfy the vortex phase distribution. At the same time, the resonant frequencies of the rectangular apertures (7) and (8) are at high and low frequency positions, respectively. Based on the spectrum synthesis and interference superposition field mechanism, the surface plasma waves excited by the inner and outer ring substructures (3) and (4) interfere at the center of the device, causing the intensity distribution of the broadband response. The magneto-optical material layer, as the substrate of the structured metal layer, is a thin film structure made of hexagonal ferrite ceramic with a thickness of 2.8 mm. Applying an external magnetic field to the magneto-optical material layer causes the incident ray deflection angle to be deflected, thereby dynamically controlling the rotation of the first-order vector vortex and the second-order vector vortex field distribution on the sheet and in free space.

[0008] The operating method of the dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascade metastructure is as follows: When the incident wave is a Y-polarized wave, the device excites a first-order vector vortex wave on the chip and a second-order vector vortex wave in free space. Simultaneously, the introduction of the magneto-optical material layer provides the device with non-volatile active control: when the applied magnetic field is -0.67 T, the Y-polarized wave incident on the bottom of the structured metal layer is deflected into a -45° linearly polarized wave, causing a 45° counterclockwise deflection of the first-order vector vortex on the chip and the second-order vector vortex in free space; when the applied magnetic field is 0.67 T, the Y-polarized wave incident on the bottom of the structured metal layer is deflected into a 45° linearly polarized wave, causing a 45° clockwise deflection of the first-order vector vortex on the chip and the second-order vector vortex in free space. The device operates in the frequency range of 0.4–0.72 THz, and the purity of the generated vortex modes can reach up to 98%.

[0009] The beneficial effects and advantages of this invention are:

[0010] 1. The dynamically modulated non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device uses a rectangular aperture structure as the basic unit of the device, which can simultaneously excite surface plasmonic waves and scattered transmitted waves, thereby realizing the modulation of on-chip two-dimensional transmission waves and free-space three-dimensional transmission waves, forming two channel modes: first-order plasmonic vortex and second-order free-space vortex.

[0011] 2. The device has two rectangular aperture structures of different sizes as basic building blocks, with different excitation spectra and resonant frequencies. Under the interference superposition mechanism, it ensures that the plasma wave on the chip surface achieves a uniform superposition field distribution in a wide range.

[0012] 3. This device integrates a magneto-optical material layer as an active modulation structure. By applying an external magnetic field, the magnetic moment state of the magneto-optical material is dynamically changed, thereby deflecting the incident beam angle and achieving rotational modulation of the vortex field distribution and polarization state distribution. Furthermore, the magneto-optical material layer can maintain its magnetic moment after the external magnetic field is removed, thus enabling non-volatile vortex field modulation.

[0013] 4. The device operates with a small external excitation magnetic field and low energy consumption. The external magnetic field applied to the magneto-optical material layer has a tuning range of -0.67 T to 0.67 T, and the vortex field distribution rotates in the range of 0-90°.

[0014] 5. The structured metal layer of this device is fabricated using ion sputtering and laser direct writing processes, which are low in cost, low in loss, and easy to prepare.

[0015] 6. This device features dynamic tuning, compact structure, and on-chip integration, which is of great significance for the development of terahertz communication systems.

[0016] Attached image description.

[0017] Figure 1 (a) is a schematic diagram of the three-dimensional structure of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device.

[0018] Figure 1 (b) is a top view of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure.

[0019] Figure 1 (c) is a side view of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure.

[0020] Figure 2 (a) is a schematic diagram of the ring substructure (3).

[0021] Figure 2 (b) is a schematic diagram of the ring substructure (4).

[0022] Figure 2 (c) is a structural schematic diagram of the rectangular hole pair (5).

[0023] Figure 2 (d) is a schematic diagram of the structure of the rectangular hole pair (6).

[0024] Figure 2 (e) is a schematic diagram of the rectangular hole (7).

[0025] Figure 2 (f) is a schematic diagram of the rectangular hole (8).

[0026] Figure 3 (a) is a schematic diagram of the working principle of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure when 45° linearly polarized light is incident.

[0027] Figure 3 (b) is a schematic diagram of the working principle of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure when incident with -45° linearly polarized light.

[0028] Figure 3 (c) is a schematic diagram of the working principle of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure when circularly polarized light is incident.

[0029] Figure 3 (d) is a schematic diagram of the working principle of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure when X-ray polarized light is incident and an external magnetic field B = 0.67 T is applied.

[0030] Figure 3 (e) is a schematic diagram of the working principle of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure when X-ray polarized light is incident and an external magnetic field B=0 T is applied.

[0031] Figure 3 (f) is a schematic diagram of the working principle of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure when X-ray polarized light is incident and an external magnetic field B = -0.67 T is applied.

[0032] Figure 4 (a) is a graph of the near-field channel time domain signal measured at a fixed observation position under different applied magnetic fields when Y-polarized light is incident.

[0033] Figure 4 (b) is the near-field intensity spectrum measured at a fixed observation position under different applied magnetic fields when Y-polarized light is incident.

[0034] Figure 4(c) is the intensity distribution curve along the direction of the vector vortex spot when Y-polarized light is incident at different operating frequencies.

[0035] Figure 5 (a) shows the intensity and phase distribution of the first-order vector vortex excited in the near-field channel of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device with incident Y-ray polarized light and an applied magnetic field of 0.67 T.

[0036] Figure 5 (b) shows the intensity and phase distribution of the first-order vector vortex excited in the near-field channel of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device with incident Y-ray polarized light and an applied magnetic field of 0.36 T.

[0037] Figure 5 (c) shows the first-order vector vortex intensity and phase distribution excited in the near-field channel of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device with incident Y-ray polarized light and an applied magnetic field of 0 T.

[0038] Figure 5 (d) shows the first-order vector vortex intensity and phase distribution excited in the near-field channel of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device with incident Y-ray polarized light and an applied magnetic field of -0.36 T.

[0039] Figure 5 (e) shows the first-order vector vortex intensity and phase distribution excited in the near-field channel of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device with incident Y-ray polarized light and an applied magnetic field of -0.67 T.

[0040] Figure 6 (a) shows the second-order vector vortex intensity, polarization state, and phase distribution of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device excited in the far-field channel when Y-polarized light is incident and an external magnetic field of -0.67 T is applied.

[0041] Figure 6 (b) shows the second-order vector vortex intensity, polarization state, and phase distribution of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device excited in the far-field channel when Y-polarized light is incident and an external magnetic field of -0.36 T is applied.

[0042] Figure 6 (c) shows the second-order vector vortex intensity, polarization state, and phase distribution of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device excited in the far-field channel when Y-polarized light is incident and an external magnetic field of 0 T is applied.

[0043] Figure 6(d) shows the second-order vector vortex intensity, polarization state, and phase distribution of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device excited in the far-field channel when Y-polarized light is incident and an external magnetic field of 0.36 T is applied.

[0044] Figure 6 (e) shows the second-order vector vortex intensity, polarization state, and phase distribution of a dynamically controlled non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device excited in the far-field channel when Y-polarized light is incident and an external magnetic field of 0.67 T is applied.

[0045] Detailed implementation method.

[0046] The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure of the present invention is described in detail with reference to the accompanying drawings. It should be noted that the present invention can be implemented with various different specific structural parameters, including but not limited to the specific examples described below.

[0047] The structure of the device is as follows Figure 1 and Figure 2 As shown, the dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded meta-device comprises: a structured metal layer (1) and a magneto-optical material layer (2). The structured metal layer is formed by adding layers of metal to a thickness of [insert thickness here]. h The inner ring structure (3) and outer ring structure (4) are formed by rectangular hole pairs (5) and (6) etched in the XY two-dimensional plane on a 200nm copper film, respectively. Among them, a pair of rectangular holes (7) with identical geometric dimensions are orthogonally placed to form a rectangular hole pair (5). The two rectangular holes (7) and x The included angles of the axes are respectively β 1 = 45° and β 2 = 135°, the lateral distance between the geometric centers is 3 / 4 of the plasma wavelength, the longitudinal distance is 0, and the frequency corresponding to the working plasma wavelength is 0.645 THz; a pair of rectangular holes (8) with identical geometric dimensions are orthogonally placed to form a pair of rectangular holes (6), and the two rectangular holes (8) and x The included angles of the axes are respectively β 3 = 135° and β 4 =The lateral distance between the geometric centers is 3 / 4 of a plasma wavelength, and the longitudinal distance is 0. The working plasma wavelength corresponds to a frequency of 0.645 THz. The distance between the rectangular hole pair (5) and the rectangular hole pair (6) is 1.16 mm. The number of rectangular hole pairs in both the inner and outer rings is 60. The angular distance between adjacent rectangular holes in the same ring is approximately 6°. The rotation angle of each rectangular hole is equal to the initial angle. β Including the spatial azimuth angle of its location. The lengths of rectangular holes (7) and (8) are 160 μm and 270 μm, respectively, and the widths are both 50 μm. The radius of the inner ring (3) is 1.625 mm, and the radius of the outer ring (4) is 2.785 mm. The magneto-optical material layer used is a hexagonal ferrite ceramic material with a thickness of d With a diameter of 2.8 mm, it exhibits Faraday rotation and ferromagnetic properties, thus enabling it to rotate the incident ray deflection angle and maintain the stability of the controlled state under an external magnetic field.

[0048] The basic working principle of this device is as follows: A subwavelength rectangular metal aperture is a typical basic structure for constructing plasmonic metasurfaces and exciting surface plasmon waves. A rectangular aperture unit with a large aspect ratio can be considered a dipole source. When incident light waves are incident from the bottom of the substrate onto the rectangular aperture unit, the intensity of the surface plasmon wave excited perpendicular to the long axis of the rectangular aperture unit is much greater than that in the short axis direction. Simultaneously, a resonant frequency point exists in the spectral distribution. The location of the resonant frequency point is related to the size and aspect ratio of the rectangular aperture. For a distance of [missing information] from the rectangular aperture... r At any point, the electric field intensity of the surface plasma wave excited therein satisfies the formula:

[0049]

[0050] in, It is the coupling coefficient, which represents the degree to which the rectangular aperture element couples the incident excitation wave to the surface plasma wave; E 0 It is to excite the amplitude. k It is the wave vector of the plasma wavelength; ψ It is the incident ray deflection angle, and α is the angle between the incident ray deflection angle and the orientation angle of the major axis of the rectangular hole; r This represents the distance from the observation point to the rectangular aperture. Based on the above formula, it can be further calculated that when the rectangular aperture is uniformly distributed along the angular direction on the inner and outer ring structures formed by four circular rings of different radii, the electric field intensity at any point inside it can be expressed as:

[0051]

[0052] in, Q A point is an observation point. Φ This indicates the spatial azimuth angle of the rectangular hole's location. dIt is a rectangular hole and Q The distance between points, λ sp It is the wavelength of the plasma wave.

[0053] Meanwhile, the rectangular aperture structure can be viewed as a two-dimensional rectangular cylinder, exhibiting anisotropy. When the incident excitation wave is circularly polarized light, the outgoing field through the transmitted rectangular aperture contains a co-polarized component that has not undergone polarization conversion and a cross-polarized component that has undergone polarization conversion. The entire process can be represented as:

[0054]

[0055] in, σ represents incident circularly polarized light, and ±1 represents left-handed and right-handed circularly polarized light, respectively. The rotation matrix corresponding to the rectangular hole in the anisotropic structure, and This refers to the complex transmission amplitudes of the major and minor axes of the rectangular aperture. More specifically, the above process can be expressed as:

[0056]

[0057] The first term represents the co-polarization component, and the second term represents the cross-polarization component carrying the geometric phase. Therefore, when the incident wave is circularly polarized, the transmission field distribution in free space exhibits a second-order vortex mode; when the incident wave is linearly polarized, it exhibits a second-order vector vortex mode.

[0058] The inner ring structure (3) and the outer ring structure (4) are composed of rectangular aperture pairs (5) and (6), respectively, and have different excitation resonant frequencies. Specifically, the peak excitation frequency of the rectangular aperture pair (5) is 0.42 THz, and the peak excitation frequency of the rectangular aperture pair (6) is 0.66 THz. Under the interference superposition mechanism, this structure-related excitation spectrum makes the vortex field inside the ring structure have a uniform intensity distribution over a wide frequency band, thereby realizing a broadband response to the incident excitation wave.

[0059] The magneto-optical material layer serves to deflect the incident linearly polarized light and maintain the non-volatile modulation state. When the incident linearly polarized excitation wave passes through the magneto-optical material layer, the magnetic moment inside the layer changes under the influence of the applied magnetic field, causing a deflection of the linear polarization angle and a rotation of the output field distribution. When the applied magnetic field strength B = 0.67 T, the linear polarization angle rotates 45° clockwise, and the on-sheet first-order vortex field and the transmitted second-order vortex field distribution rotate 45° clockwise, while the polarization state distribution rotates 90°. When the applied magnetic field strength B = -0.67 T, the linear polarization angle rotates 45° counterclockwise, and the on-sheet first-order vortex field and the transmitted second-order vortex field distribution rotate 45° counterclockwise, while the polarization state distribution rotates 90°. Simultaneously, when the external magnetic field is removed, the magnetic moment within the magneto-optical material layer remains unchanged, ensuring that the entire modulation state does not change with the disappearance of the external magnetic field, thus providing non-volatile modulation capability.

[0060] The working method of this device is as follows: Figure 3 This is a schematic diagram of the device's operation. When no external magnetic field is applied and the incident light is polarized, the surface plasma wave excited in the near-field channel interferes at the center of the device, generating a first-order vector vortex. At the same time, the freely scattered light, due to the geometric phase caused by the rectangular aperture, satisfies the vortex phase distribution, forming a second-order vector vortex field distribution in the far-field channel. When the applied magnetic field strength is 0 and the incident wave is circularly polarized, first-order and second-order vortex field distributions are generated in the near-field and far-field channels, respectively. When an external magnetic field B = 0.67 T is applied and the incident wave is X-polarized linearly polarized light, the X-polarized light incident on the bottom of the structured metal layer is deflected to -45° linearly polarized light due to the effect of the magneto-optical material layer, causing the near-field and far-field vector vortex field distributions to rotate clockwise by 45°. When an external magnetic field B = -0.67 T is applied and the incident wave is X-polarized linearly polarized light, the X-polarized light incident on the bottom of the structured metal layer through the magneto-optical material layer is deflected to 45° linearly polarized light, causing the near-field and far-field vector vortex field distributions to rotate counterclockwise by 45°. The specific functional parameters of this device will be discussed later. Figures 4 to 6 It is displayed in the middle.

[0061] Figure 4 The intensity distribution of plasma waves on the surface of the structured metal layer under different magnetic fields was quantitatively analyzed. The maximum intensity of the vector vortex was selected as the reference point, and the time-domain signal distribution at this point was measured successively at magnetic field strengths of ±0.67 T. Figure 4 As shown in (a), the signal amplitude measured in the range of 5 to 25 ps when the magnetic field strength is B = -0.67 T is much larger than that when the magnetic field strength is B = 0.67 T, indicating that the distribution of the vector vortex field is rotated by applying a magnetic field, resulting in a completely different signal distribution measured at the same location. Figure 4(b) describes the spectral distribution of the time-domain signal after Fourier transform. When B = −0.67 T, the intensity distribution at the reference point is stronger in the range of 0.2–0.65 THz than that corresponding to B = 0.67 T. This is consistent with… Figure 4 (a) The displayed results are consistent. Figure 4 (c) describes the intensity distribution along the center line of the two light spots of the vector vortex. The intensity field at the low frequency point is more compact than the field intensity distribution at the high frequency point, which specifically illustrates the distribution of the vector vortex at different frequencies.

[0062] Figure 5 (a)–(e) show the on-chip surface plasmon wave distribution excited by the device at 0.3 THz under different magnetic fields. When no magnetic field is applied, Y-polarized light is incident from the bottom of the structured metal layer; when a magnetic field of 0.67 T is applied, the Y-polarized light is deflected to 45° and incident from the bottom of the structured metal layer; when a magnetic field of -0.67 T is applied, the Y-polarized light is deflected to -45° and incident from the bottom of the structured metal layer. As the magnetic field strength increases, the excited first-order vector vortex intensity distribution on the chip rotates clockwise, with the magnitude of rotation being the same as the magnitude of the deflection of the linearly polarized light incident on the structured metal layer substrate, and the rotation range is 0–90°.

[0063] Figure 6 (a)~(e) show the far-field intensity, polarization state, and phase distribution of the device at a distance of 5 mm from the structured metal layer when a magnetic field strength is applied from -0.67 T to 0.67 T at 0.3 THz. When no magnetic field is applied, Y-polarized light is incident from the bottom of the structured metal layer; when a magnetic field of 0.67 T is applied, the Y-polarized light is deflected to 45° and incident from the bottom of the structured metal layer; when a magnetic field of -0.67 T is applied, the Y-polarized light is deflected to -45° and incident from the bottom of the structured metal layer. With increasing magnetic field strength, the entire second-order vector vortex field deflects clockwise, with the intensity distribution deflection being the same as the linear deflection angle, while the polarization state distribution deflection is twice the magnitude of the linear deflection angle. This deflection of the field intensity distribution demonstrates that the introduction of the magneto-optical material layer and the addition of an external magnetic field provide a powerful solution for the active control of the dual-channel vortex field.

[0064] In summary, through structural design, this device achieves dual-channel excitation of on-chip first-order plasma vortices and free-space second-order vortices over a wide bandwidth, overcoming the shortcomings of previous vortex generators, such as single operating channel, narrow operating bandwidth, and lack of tunability. The device employs ion sputtering and laser direct writing processes, offering advantages such as low cost, low loss, and ease of fabrication. Utilizing magneto-optical materials as the active modulation technique enables significant functional switching under low external excitation. Furthermore, the inherent ferromagnetism of the magneto-optical materials contributes non-volatility during dynamic modulation, making the device suitable for a wider range of applications. This dynamically modulated, non-volatile, broadband terahertz dual-channel vortex magneto-optical cascade metastructure, with its dynamic tuning, broadband response, and dual-channel operating modes, is of great significance for the development of terahertz wireless communication and information processing.

Claims

1. A dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure, characterized in that, The device is arranged in sequence as a structured metal layer (1) and a magneto-optical material layer (2); wherein, the structured metal layer (1) is composed of ring substructures (3) and (4), the outermost ring radius is not greater than 5 mm, and the innermost ring radius is not less than 1.95 mm; the ring substructures (3) and (4) are composed of orthogonal rectangular aperture pairs (5) and orthogonal rectangular aperture pairs (6) with an arbitrary value of adjacent relative azimuth angle in the range of 6°~25°, respectively, and are uniformly distributed along the angular direction; the orthogonal rectangular aperture pairs (5) and (6) are composed of a pair of rectangular apertures (7) and (8) with identical geometric dimensions and mutually perpendicular major axes, and the aspect ratio of the apertures ranges from 15:6 to 31:4; under linear polarized light incident excitation, the structured metal layer (1) realizes broadband response first-order plasma vortex and second-order free space vortex in the near field and far field, respectively; by applying -0.67 T-0.67 to the magneto-optical material layer (2). A magnetic field within the range of T can be used to control the polarization angle of the incident ray-polarized wave, dynamically rotating the vortex field and polarization state distribution on the sheet and in free space.

2. The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure according to claim 1, characterized in that, The structured metal layer (1) is made by laser direct writing process to obtain patterned metal rectangular holes (7) and metal rectangular holes (8) on a copper metal thin film with a thickness of 100~200 nm by ion sputtering. The long side dimension of the metal rectangular hole (7) is 150~220 μm and the short side dimension is 40~60 μm; the long side dimension of the metal rectangular hole (8) is 230~310 μm and the short side dimension is 40~60 μm. Different geometric dimensions of the metal rectangular holes correspond to different resonant frequencies, ensuring that the spectrum of surface plasma waves synthesized by different sizes is uniformly distributed in the broadband range.

3. The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure according to claim 1, characterized in that, The initial orientation angle β of the major axis of the two orthogonally oriented rectangular hole pairs (7) in the orthogonal rectangular hole pair (5) 1 and β 2 The initial orientation angles β of the major axes of the two orthogonally oriented rectangular holes (8) in the orthogonal rectangular hole pair (6) are 45° and 135° respectively. 3 and β 4 The major axes of all rectangular holes in the structured metal layer (1) are 135° and 45° respectively, relative to... x The included angle of the axis is the initial orientation angle β plus the spatial azimuth angle of its position. The relative distances in the transverse and longitudinal directions of the geometric centers of the orthogonal rectangular holes (5) and (6) in the structured metal layer (1) are respectively and , λ 0 It is the wavelength of surface plasma. θ It is the spatial azimuth angle of the orthogonal rectangular hole pair in the structured metal layer (1).

4. The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure according to claim 1, characterized in that, The ring structures (3) and (4) are arranged in an inner and outer ring configuration. All pairs of orthogonal rectangular holes (5) and (6) are uniformly distributed angularly and oriented radially to ensure that the plasma waves excited by the incident light on the inner and outer ring surfaces have a transmission phase difference and propagate radially, superimposing and interfering at the center of the ring to form a vortex field; the radius of the ring substructure (3) r 1 and the radius of the ring substructure (4) r 2 Not less than and , L 1 and L 2 These are the lengths of the rectangular holes (7) and (8), respectively; N It is the number of rectangular holes on the annular substructures (3) and (4).

5. The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure according to claim 1, characterized in that, For the structured metal layer (1), when the external excitation is a circularly polarized wave, a first-order plasma vortex and a second-order free space vortex are formed in the near field and far field, respectively; when the external excitation is a linearly polarized wave, a first-order vector plasma vortex and a second-order vector free space vortex are formed in the near field and far field, respectively.

6. The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure according to claim 1, characterized in that, The magneto-optical material layer (2) has a thickness of 2.8 mm and exhibits Faraday rotation and ferromagnetism. Its inherent physical properties bring about the non-volatility of the incident light deflection angle rotation and the control state, which means that the magneto-optical material layer still maintains the control state after the external excitation is removed. At the same time, the rotation direction of the linear deflection angle is independent of the incident wave transmission direction and is only related to the electron spin in the material, thus breaking the Lorentz reciprocity in transmission. When the applied magnetic field strength is in the range of -0.67 T to 0.67 T, the polarization angle rotation range of the incident linearly polarized wave is -45° to 45°.

7. The dynamically tunable non-volatile broadband terahertz dual-channel vortex magneto-optical cascaded metastructure according to claim 1, characterized in that, When an external magnetic field strength greater than 0 is applied, the incident Y-polarized wave is deflected clockwise, causing the field distribution and polarization state distribution of the first-order and second-order vector vortices to deflect clockwise; when an external magnetic field strength less than 0 is applied, the incident Y-polarized wave is deflected counterclockwise, causing the field distribution and polarization state distribution of the first-order and second-order vector vortices to deflect counterclockwise.

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