An adjustable terahertz magneto-optical chiral metasurface deflector

Abstract

The application discloses a tunable terahertz magneto-optical super surface deflector, which is composed of superlattice arranged period units, each superlattice includes an InSb substrate and a pair of orthogonal Si columns and InSb columns. Without a magnetic field, the device uses destructive interference to suppress the phase control function, realizes the direct transmission of the light beam, at this time, the polarization conversion rate of the superlattice is less than 15%, and the light beam transmittance is higher than -5dB. Then, using the tunability and magneto-optical effect of magneto-optical materials, the superlattice realizes the chiral phase modulation function based on the active regulation of the magnetic field, and the polarization conversion circular dichroism is more than 98%. Based on this, the device realizes selective deflection of chiral light, and in the working frequency band, the deflection angle ranges from 15.9° to 23.4°. The tunable chiral deflection function of the device makes it have great application potential in terahertz spectrum, communication, scanning imaging and other systems.

Description

Technical Field

[0001] This invention belongs to the field of terahertz science and technology, specifically relating to a terahertz beam deflection device that has chiral selectivity for incident circularly polarized light and can be actively controlled. Background Technology

[0002] Terahertz waves refer to electromagnetic waves with frequencies ranging from 0.1 to 10 THz, falling between microwaves and the infrared band. They possess advantages such as low photon energy, high frequency, and large usable bandwidth, showing great promise for applications in non-destructive testing, biomedicine, military, astronomy, and environmental fields. In recent years, with the development of terahertz technology, the demand for multifunctional terahertz devices has increased. Among them, beam deflectors, capable of altering wavefront phase and manipulating beam propagation direction, play a crucial role in terahertz communication and detection.

[0003] Metasurfaces offer a crucial solution for achieving phase modulation. When the mid-unit structure of a metasurface can function as a half-wave plate, this unit can achieve cross-polarization of circularly polarized light and introduce a geometric phase, thus enabling phase modulation. When the introduced geometric phase tilts the wavefront, deflection is achieved, with the introduced deflection angle obeying the generalized Snell's law [Science, 2011, 334:333-337]. Based on this idea, M. Khorasaninejad et al. achieved the deflection of incident beams in the 975nm band [Nat. Commun., 2014, 5:5386], separating left-handed and right-handed incident beams. Compared to traditional optics methods using optical crystals for beam deflection, metasurfaces offer advantages such as thinness, high integration, and the ability to design the deflection direction based on structural design. However, this device, which achieves wavefront tilting through geometric phase, causes left-handed and right-handed light to bend in symmetrical directions, making it impossible for the device to perform phase modulation on these chiral lights separately, and thus also impossible to selectively deflect a chiral light.

[0004] To enable devices to independently control left-handed and right-handed light, some researchers have attempted to achieve this by designing chiral structures. For example, in 2017, AYZhu et al. used a chiral "swastika"-shaped structure to achieve chiral modulation of left-handed and right-handed light. This device caused right-handed light to diffract towards the 0th order and left-handed light towards the ±1st order, achieving chiral deflection [LightSci.Appl.,2018,7:17158]. However, the deflection direction of this device depends on the unit cell period, and the operating wavelength also changes with the unit cell size, thus limiting the design of the deflection angle. Furthermore, the optical chirality of such devices is based on the chirality of the structure. Since the structure is fixed once fabricated, these devices generally always possess chirality and cannot have their chiral function turned off. Another method to achieve optical chirality is to use chiral materials, among which magneto-optical materials are the most prominent. Under the influence of an external magnetic field, left-handed and right-handed light will have different propagation constants in magneto-optical materials, thus leading to chiral absorption or optical rotation. Therefore, in previous studies, magneto-optical materials have typically been used as the basic components of isolators or polarization converters, and their complex electromagnetic properties require further development. It is noteworthy that no device has yet utilized magneto-optical materials to achieve chiral deflection, meaning it cannot selectively deflect a single chiral light. Furthermore, magneto-optical materials possess active tunability, providing a theoretical tool to overcome the limitation of chiral structures being unable to shut down chiral functions in passive conditions.

[0005] In summary, firstly, selectively deflecting single-chiral light remains challenging; secondly, due to the fixed structure of metamaterials, actively tunable devices still hold research value; thirdly, in practical applications, removing and inserting the device for adjustment is a complex process, thus a switch that enables the function has practical application value; fourthly, since external sources often consume energy, especially tunable magnetic field sources typically generated by energized coils, allowing the beam to pass directly through the device in passive mode and activating the device's function in active mode has greater practical application value. Because the research reported domestically and internationally cannot simultaneously meet these four requirements, there is an urgent need for a terahertz deflector with chiral selection capability, active tunability, the ability to disable modulation in passive mode, and the ability to quickly and easily activate modulation. Summary of the Invention

[0006] The purpose of this invention is to provide an actively adjustable terahertz chiral deflector, which enables direct light beam transmission in a passive state and selective deflection of chiral light through an external magnetic field. This addresses key technical problems in the prior art, such as the inability of terahertz deflectors to chirp and the difficulty in switching and controlling device functions.

[0007] The technical solution of this invention is as follows: A tunable terahertz magneto-optical chiral metasurface deflector uses high-resistivity silicon (Si) and indium antimonide (InSb) as materials, where InSb is an important magneto-optical material in the terahertz band. The device consists of Si pillars, InSb pillars, and an InSb substrate. One Si pillar and one InSb pillar stand upright on the InSb substrate, forming a supercell, which is the smallest functional unit of the device. A supercell can be divided into two sub-units: an InSb unit containing the InSb pillar and the InSb substrate, and a Si unit containing the Si pillar and the InSb substrate, where the long sides of the InSb pillar and the Si pillar are orthogonally oriented. In the absence of a magnetic field, because the geometric phase difference between the orthogonal InSb pillar and the Si pillar is 180°, the cross-polarization components emitted from the two sub-units produce destructive interference, suppressing cross-polarization and ensuring direct light transmission. In the presence of an external magnetic field, the electromagnetic properties of the magneto-optical material change, disrupting the destructive interference that suppresses cross-polarization and increasing the cross-polarization component. Furthermore, utilizing the circular dichroism of the InSb substrate, selective cross-polarization is achieved for a single chiral light source, allowing another chiral light to pass directly through. Subsequently, six supercells are arranged according to a geometric phase pattern to form a periodic unit, where the Si pillar orientation angles within the supercells differ by 30° sequentially, resulting in a 60° geometric phase difference between adjacent supercells. This arrangement allows the geometric phases of the supercells within a periodic unit to be sequentially 0°, 60°, 120°, 180°, 240°, and 300°, thereby achieving a wavefront tilting function. Periodic extension of this periodic unit yields the tunable terahertz magneto-optical chiral metasurface deflector.

[0008] The tunable terahertz magneto-optical chiral metasurface deflector comprises: a Si pillar (1) with a length of 95–105 μm, a width of 55–65 μm, and a height of 500 μm; an InSb pillar (2) with a length of 105–115 μm, a width of 65–75 μm, and a height of 500 μm; and an InSb substrate (3) with a thickness of 100–200 μm. The intrinsic carrier concentration of the magneto-optical material InSb is 4 × 10⁻⁶. 14 cm -3 Each supercell (4) has a length of 280 μm and a width of 140 μm.

[0009] The tunable terahertz magneto-optical chiral metasurface deflector operates as follows: The device is placed in a terahertz optical path within an environment of 70K–90K. An external bias magnetic field is applied along the propagation direction for adjustment, with the magnetic induction intensity of the bias magnetic field between ±0.3T. Incident light is perpendicularly incident on the metasurface deflector, operating in the frequency range of 0.45THz–0.65THz. When the external bias magnetic field is 0T, the beam passes directly through the device without wavefront phase modulation, thus no deflection occurs. When an external magnetic field is present, chiral deflection is achieved. Under a positive bias magnetic field, incident right-handed circularly polarized light is deflected by the device, while left-handed circularly polarized light passes directly. Under a negative bias magnetic field, incident left-handed circularly polarized light is deflected by the device, while right-handed circularly polarized light passes directly. The deflection angle of right-handed light incident under a positive bias magnetic field is opposite to that of left-handed light incident under a negative bias magnetic field. Within the operating frequency band, the deflection angle ranges from 15.9° to 23.4°.

[0010] The beneficial effects and advantages of this invention are:

[0011] 1. This device cleverly utilizes the principle of destructive interference to strongly suppress the phase modulation function of the supercell in the absence of a magnetic field. Under these conditions, the polarization conversion rate is below 15% within the operating range, while maintaining high transmittance, which is around -5dB. This makes the device's influence on the light beam negligible, effectively ensuring direct light transmission and overcoming the limitation of traditional chiral structure devices that cannot shut down device functionality.

[0012] 2. This device utilizes, and requires only, a magnetic field to simultaneously achieve selective and active modulation of chiral light, with the required magnetic field ranging from ±0.3T, and operating optimally at ±0.25T. This magnetic field is readily available, making modulation more convenient compared to traditional chiral tunable devices.

[0013] 3. This device is a broadband deflector with an operating frequency band of 0.45THz-0.65THz, which expands the operating range compared to the narrow operating frequency band of traditional deflectors.

[0014] 4. This device exhibits excellent chiral deflection capability under a magnetic field. Specifically, under a positive magnetic field, the polarization conversion efficiency of a single supercell for right-handed circularly polarized light exceeds 97%, and the circular dichroism of the polarization conversion exceeds 98%. Similarly, under a negative magnetic field, the polarization conversion efficiency of a single supercell for left-handed circularly polarized light also exceeds 97%, and the circular dichroism of the polarization conversion also exceeds 98%. This indicates that, within the operating frequency band and under an applied magnetic field, this device can emit extremely pure deflected light for one chiral state while suppressing almost all directly transmitted components; correspondingly, for the other chiral state, it produces extremely pure directly transmitted light without any deflection components. Therefore, this device possesses chiral deflection capabilities, filling a gap in previous research and giving it enormous application potential in terahertz communication, detection, and other fields. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an adjustable terahertz magneto-optical chiral metasurface deflector;

[0016] Figure 2 (a) is a schematic diagram of the three-dimensional structure of a supercell;

[0017] Figure 2 (b) is a front view of the supercell;

[0018] Figure 2 (c) is a top view of the supercell;

[0019] Figure 3 (a) Schematic diagram of the operation of the tunable terahertz magneto-optical metasurface deflector at 0.25T;

[0020] Figure 3 (b) Schematic diagram of the operation of the tunable terahertz magneto-optical metasurface deflector at -0.25T;

[0021] Figure 4 (a) Transmittance spectrum of a single supercell at 0T;

[0022] Figure 4 (b) Transmittance spectrum of a single supercell at 0.25T;

[0023] Figure 4 (c) Transmittance spectrum of a single supercell at -0.25T;

[0024] Figure 5 (a) shows the change in the emission phase as a function of the orientation angle of the InSb pillars when LCP is incident on a single supercell in the absence of a magnetic field.

[0025] Figure 5 (b) shows the change in the emission phase as a function of the orientation angle of the InSb pillars when RCP is incident on a single supercell in the absence of a magnetic field.

[0026] Figure 5 (c) shows the change in the emission phase as a function of the orientation angle of the InSb pillars when LCP is incident on a single supercell in a magnetic field of 0.25T.

[0027] Figure 5 (d) shows the change in the emission phase as a function of the orientation angle of the InSb pillars when RCP is incident on a single supercell in a magnetic field of 0.25T.

[0028] Figure 5 (e) shows the change in the emission phase as a function of the orientation angle of the InSb pillars when LCP is incident on a single supercell at a magnetic field of -0.25T.

[0029] Figure 5 (f) shows the change in the emission phase as a function of the orientation angle of the InSb pillars when RCP is incident on a single supercell at a magnetic field of -0.25T.

[0030] Figure 6 (a) is the diffraction spectrum of the tunable terahertz magneto-optical chiral metasurface deflector under LCP incident in the absence of a magnetic field;

[0031] Figure 6 (b) is the diffraction spectrum of the tunable terahertz magneto-optical chiral metasurface deflector under RCP incident without magnetic field.

[0032] Figure 6 (c) is the diffraction spectrum of the tunable terahertz magneto-optical chiral metasurface deflector under LCP incident at a magnetic field of 0.25T.

[0033] Figure 6 (d) is the diffraction spectrum of the tunable terahertz magneto-optical chiral metasurface deflector under RCP incident at a magnetic field of 0.25T.

[0034] Figure 6 (e) is the diffraction spectrum of the tunable terahertz magneto-optical chiral metasurface deflector under LCP incident at a magnetic field of -0.25T.

[0035] Figure 6 (f) is the diffraction spectrum of the tunable terahertz magneto-optical chiral metasurface deflector under RCP incident at a magnetic field of -0.25T.

[0036] Among them, Si pillar (1), InSb pillar (2), InSb substrate (3), supercell (4), periodic unit (5), Si unit (6); InSb unit (7). Detailed Implementation

[0037] The working principle and method of this invention will be illustrated by the following examples:

[0038] The structural diagram of the device is as follows Figure 1As shown, Figure 1 In the middle (4), there is a supercell with a length p1 of 280 μm and a width p2 of 140 μm. (5) is a periodic unit consisting of six supercells. Figure 2 (a) shows a schematic diagram of a supercell structure, where (1) is a Si pillar, (2) is an InSb pillar, and (3) is an InSb substrate. The height h1 of the Si pillar (1) and the InSb pillar (2) is 500 μm, and the thickness h2 of the InSb substrate (3) is 140 μm. Figure 2 (b) and Figure 2 (c) are the front and top views of the supercell, respectively. The Si pillar (1) is located at the center of half of the InSb substrate (3) to form a Si unit (6), and the InSb pillar (2) is located at the center of the other half of the InSb substrate (3) to form an InSb unit (7). The length and width of the Si unit (6) and the InSb unit (7) are both 140 μm. The length and width of the Si pillar (1) are l1 = 110 μm and w1 = 70 μm, respectively, and the length and width of the InSb pillar (2) are l2 = 100 μm and w2 = 60 μm, respectively. Figure 2 In (c), the orientation angle of the Si pillar (1) is like Figure 1 As shown in a periodic unit (5) The orientation angles of the InSb column (2) were successively set to 0°, 30°, 60°, 90°, 120° and 150°, while the orientation angle of the InSb column (2) was also adjusted. Orientation angle with Si pillar (1) The difference is 90°.

[0039] The basic working principle of this device is as follows: InSb is a magneto-optical material whose dielectric constant is a tensor, which can be represented as follows:

[0040]

[0041] In the absence of a magnetic field, ε2 is 0, and the dielectric tensor of InSb is a diagonal matrix, exhibiting properties typical of ordinary semiconductor materials. In the presence of a magnetic field, InSb exhibits circular dichroism. For example, under a positive magnetic field, right-handed light experiences greater loss in InSb, while left-handed light experiences less loss. This provides an important theoretical tool for device design. Furthermore, ε1 and ε2 change with the magnetic field, laying the foundation for tuning.

[0042] When the geometric phases of a supercell are arranged in an arithmetic sequence to form a period, the resulting periodic unit possesses deflection capability, and its deflection angle obeys the generalized Snell's theorem [Science, 2011, 334:333-337]:

[0043]

[0044] Where dΦ is the phase variation with distance, the phase difference between every two supercells in the device described in this paper is π / 3, and the length of the supercell is 280 μm, so dΦ / dx=60° / 280μm=π / 840rad·μm -1 θ i It is the angle of incidence, θ t Let n be the launch angle. i and n t Here, represents the refractive index of the medium in which the incident and emitted rays are located; in this case, both are air and have a refractive index of 1. Therefore, under perpendicular incidence, the deflection angle of the designed device follows:

[0045]

[0046] In the absence of a magnetic field, InSb material is chiral and behaves like a typical semiconductor, so both subunits can generate cross-polarization components, introducing a geometric phase. Since the long sides of the InSb pillars and Si pillars are orthogonal, the resulting geometric phases differ by 180°. In this way, the cross-polarization components generated by both units form destructive interference, thereby suppressing the cross-polarization components of the supercell, resulting in the supercell emitting more of the directly transmitted component. Theoretically, the suppression of cross-polarization components in the overall supercell output is optimal when the cross-polarization components of the InSb and Si units are of equal magnitude.

[0047] With an applied bias magnetic field, the tuning capability of InSb can alter the magnitude of the cross-polarization component generated by the InSb unit cell, thus disrupting the destructive interference that suppresses the cross-polarization component of the supercell. Furthermore, due to the magneto-optical effect, the InSb unit cell cannot be simply considered as a semiconductor unit generating geometric phase. The geometric phase introduced by InSb cross-polarization is more complex, differing from the geometric phase generated by the InSb unit cell without a magnetic field. This results in the geometric phase difference between the emitted signals from the InSb and Si units no longer being 180°, further disrupting the destructive interference that suppresses the cross-polarization component of the supercell. Through proper structural design, the supercell can generate a larger cross-polarization component. In this case, the geometric phase introduced by the supercell during cross-polarization becomes a key factor in modulating the wavefront. Simultaneously, because the magnetic field imparts circular dichroism to InSb, it can filter out one of a pair of chiral beams. Therefore, the InSb substrate can serve as a tool for chiral selection, enabling devices to exhibit more pronounced chirality. Under a positive magnetic field, the InSb substrate filters out right-handed light. The direct transmission component generated by the supercell after right-handed light incident is still right-handed, thus being filtered out. Meanwhile, left-handed light, generated through cross-polarization and carrying geometric phase information, can exit the supercell. Conversely, for left-handed light incident, the right-handed light generated by cross-polarization is filtered out, retaining only the direct transmission component, which lacks phase information. Thus, we achieve phase modulation of a single chiral light under a magnetic field.

[0048] The specific working method of this device is as follows: Figure 3 The diagram shows the working principle of the device. When placed in a terahertz optical path and in an 80K environment, light of 0.45THz-0.65THz is incident. Without a magnetic field, the device automatically disables its deflection function, allowing the light beam to pass through directly. Figure 3 As shown in (a), when a magnetic field of +0.25T is used, the device will generate cross-polarization of the right-handed incident light, emit left-handed light, and introduce a geometric phase, thereby deflecting the right-handed incident light. At this time, the deflection angle follows formula (3), while the left-handed incident light passes through directly; Figure 3 As shown in (b), under a -0.25T magnetic field, the left-handed incident light is deflected, and the deflection angle still follows formula (3), and is opposite to the deflection angle of the right-handed incident light under a positive magnetic field. Simultaneously, the right-handed incident light passes directly through. The functional parameters of this device will be... Figures 4 to 6 Specific display.

[0049] Figure 4 These are the transmittance spectra of a single supercell. Mode 1 in the figure represents left-handed light, and mode 2 represents right-handed light. For example... Figure 4As shown in (a), in the absence of a magnetic field, within the operating frequency band, a single supercell exhibits a high direct transmission component, around -5 dB, while the conversion component is very low, below -20 dB. Figure 4 As shown in (a) and 4(b), under a magnetic field of +0.25T, when left-handed light is incident, the output is mainly left-handed light that is directly transmitted; when right-handed light is incident, the output is mainly left-handed light generated by right-handed light cross-polarization. Correspondingly, under a magnetic field of -0.25T, when right-handed light is incident, the output is mainly right-handed light that is directly transmitted; when left-handed light is incident, the output is mainly right-handed light generated by left-handed light cross-polarization. The polarization conversion rate and the polarization conversion circular dichroism are defined by formulas (4) and (5), respectively:

[0050]

[0051]

[0052] At this point, in the presence of a magnetic field, the polarization conversion rate of the supercell exceeds 97% for the chiral light that is deflected. In addition, the circular dichroism of the polarization conversion of the supercell also exceeds 98%.

[0053] Figure 5 It refers to the change in the phase of the emitted light from a single supercell with respect to the orientation angle of the Si pillars. For example... Figure 5 (a) and Figure 5 As shown in (b), neither the left-handed nor the right-handed light that passes directly through has geometric phase information. Figure 5 (c) and Figure 5 As shown in (d), under a magnetic field of +0.25T, only right-handed incident circularly polarized light with cross-polarization can generate geometric phase information. This phase depends on the orientation angle of the Si pillar and decreases as the angle increases. Correspondingly, as... Figure 5 (e) and Figure 5 As shown in (f), under a magnetic field of -0.25T, only left-handed incident circularly polarized light can generate geometric phase information, and this phase increases with the Si pillar orientation angle. The different trends of the two polarizations with the Si pillar angle are the reason for their opposite deflection directions.

[0054] Figure 6 This is the diffraction spectrum of a tunable terahertz magneto-optical chiral metasurface deflector, reflecting the relationship between the deflection angle and frequency under normal incidence. Within the operating frequency band of 0.45 THz-0.65 THz, such as... Figure 6 (a) and Figure 6 As shown in (b), the beam is mainly concentrated at 0°, with no deflection. Figure 6 (c) and Figure 6As shown in (d), under a magnetic field of +0.25T, the transmitted light from a left-handed incident beam remains concentrated at 0°, while the right-handed beam is deflected. The deflection angle follows formula (3), and within the operating frequency band of 0.45THz-0.65THz, the deflection angle ranges from +15.9° to +23.4°. Correspondingly, as... Figure 6 (e) and Figure 6 As shown in (f), under a magnetic field of -0.25T, left-handed light is deflected, while right-handed light remains directly transmitted. The deflection angle still follows formula (3), and the deflection direction is opposite to that of right-handed light under a positive magnetic field. The deflection angle range is -15.9° to -23.4°.

[0055] In summary, this device utilizes destructive interference to effectively suppress the phase modulation function of the supercell in the absence of a magnetic field, ensuring direct beam transmission and overcoming the limitation of traditional devices that cannot shut down their function in passive conditions. Dynamic control is achieved through a magnetic field, realizing chiral deflection. The supercell's polarization conversion circular dichroism exceeds 98%, indicating excellent chirality, with deflection angles ranging from 15.9° to 23.4°. This device fills the gap in tunable chiral deflectors, and its compact structure facilitates integration, allowing for widespread application in integrated and miniaturized terahertz devices or systems. It demonstrates significant application potential in terahertz communication, radar scanning, and non-reciprocal systems.

Claims

1. A tunable terahertz magneto-optical chiral metasurface deflector, characterized in that, The device consists of a Si pillar (1), an InSb pillar (2), and an InSb substrate (3). A Si pillar (1) and an InSb pillar (2) stand upright on the InSb substrate (3) to form a supercell (4). The long sides of the Si pillar (1) and the InSb pillar (2) in the supercell (4) are orthogonal. A set of supercells with continuously changing orientation angles of Si pillars (1) and InSb pillars (2) constitutes a periodic unit (5). The periodic unit (5) is periodically extended in the X and Y directions to obtain the tunable terahertz magneto-optical chiral metasurface deflector. The incident circularly polarized light is incident from above the tunable terahertz magneto-optical chiral metasurface deflector along the -Z direction. The positive bias magnetic field is along the +Z direction, and the negative bias magnetic field is along the -Z direction. The Z direction is defined as the direction perpendicular to the surface.

2. The tunable terahertz magneto-optical chiral metasurface deflector according to claim 1, characterized in that, A supercell (4) can be divided into two subunits, namely the Si unit (6) composed of Si pillars (1) and InSb substrate (3) and the InSb unit (7) composed of InSb pillars (2) and InSb substrate (3); the period of both Si unit (6) and InSb unit (7) is 140μm×140μm, and the length of the supercell is 280μm and the width is 140μm; the thickness of InSb substrate (3) is 100~200μm; in each supercell (4), the Si pillar (1) is an anisotropic cuboid with a length of 95~105μm, a width of 55~65μm and a height of 500μm; the InSb pillar (2) is an anisotropic cuboid with a length of 105~115μm, a width of 65~75μm and a height of 500μm.

3. The tunable terahertz magneto-optical chiral metasurface deflector according to claim 1, characterized in that, A periodic unit (5) contains six supercells (4), each of which has the function of introducing different geometric phases; the X direction is defined as the direction parallel to the device and along the long side of the supercell (4). Along the +X direction, the orientation angles of the Si pillar (1) are 0°, 30°, 60°, 90°, 120° and 150°, respectively. The orientation angles of the corresponding InSb pillars orthogonal to it are 90°, 120°, 150°, 0°, 30° and 60°, respectively. At this time, in the presence of a bias magnetic field, the geometric phase difference introduced between two adjacent supercells (4) is π / 3.

4. The tunable terahertz magneto-optical chiral metasurface deflector according to claim 1, characterized in that, The intrinsic carrier concentration of the magneto-optical material InSb used in the InSb column (2) and the InSb substrate (3) is 4*10 14 cm -3 -3, the bias magnetic field is a weak and stable magnetic field provided by an electromagnetic coil, the magnetic induction intensity of which is between ±0.3T, and the working environment temperature of the adjustable terahertz magneto-optical chiral metasurface deflector is between 70K and 90K.

5. The tunable terahertz magneto-optical chiral metasurface deflector according to claim 1, characterized in that, When the bias magnetic field is turned off, the geometric phases generated by the Si unit (6) and the InSb unit (7) in a single supercell differ by 180°, forming destructive interference and turning off the phase modulation function. At this time, since the deflection function of the deflector is based on the gradient phase arrangement of the supercell, turning off the phase modulation function of the supercell is equivalent to turning off the deflection function of the device, ensuring that the beam passes directly through the device. In the working frequency band of 0.45THz-0.65THz, the transmittance is around -5dB.

6. The tunable terahertz magneto-optical chiral metasurface deflector according to claim 1, characterized in that, In the presence of a bias magnetic field, the destructive interference of the geometric phase is disrupted. Simultaneously, the chirality of the magneto-optical material InSb enables the device to achieve chiral selective deflection. When the bias magnetic field is positive, right-handed circularly polarized light incident on the supercell will be deflected by a tunable terahertz magneto-optical chiral metasurface deflector. Within the operating frequency band of 0.45THz-0.65THz, the deflection angle ranges from +15.9° to +23.4°. Meanwhile, left-handed circularly polarized light incident on the supercell will pass through directly, unaffected by phase modulation. When the bias magnetic field is reversed, right-handed circularly polarized light incident on the supercell will pass through directly, while left-handed circularly polarized light incident on the supercell will be deflected. The deflection direction is opposite to that of right-handed circularly polarized light incident under a positive magnetic field, with a deflection angle range of -15.9° to -23.4°. At this point, the polarization conversion circular dichroism generated by the supercell exceeds 98%, and the device exhibits chiral selectivity.

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