Amplitude-tunable terahertz metasurface polarization selector and use method thereof

Abstract

The invention belongs to the technical field of terahertz technology application, and discloses an amplitude-tunable terahertz metasurface polarization selector and a use method thereof. The terahertz metasurface polarization selector comprises a medium silicon substrate, a medium silicon column microstructure basic unit array arranged on the surface of the medium silicon substrate and a liquid crystal layer arranged on the back face of the medium silicon substrate. Each medium silicon column microstructure basic unit is composed of two silicon column unit structures of an isotropic silicon column unit and an anisotropic silicon column unit, and a medium silicon substrate. According to the invention, a diatom interference design is adopted, a transparent effect on linear polarization terahertz waves at a specific angle is realized, and an asymmetric transmission function is realized; meanwhile, liquid crystal is introduced to realize a dynamic amplitude tuning function of the metasurface; the wavefront shaping function of the metasurface is realized by introducing gradient phase design. The terahertz metasurface polarization selector is simple in structure and easy to process, can be widely applied to the fields of terahertz communication and imaging, and provides a new thought for design of terahertz polarization selection devices.

Description

Technical Field

[0001] This invention relates to the field of terahertz technology application technology, and in particular to an amplitude-tunable terahertz metasurface polarization selector and its usage method. Background Technology

[0002] Terahertz waves typically range in frequency from 0.1 THz to 10 THz, falling between microwaves and infrared. Terahertz waves possess unique physical properties, such as high transmittance to nonpolar materials (fabrics, ceramics, etc.), water absorption, low energy, broadband bandwidth, and coherence. These properties make terahertz technology a promising candidate for applications in non-destructive testing, biomedical imaging, security inspection, and ultra-high-speed, high-capacity wireless communication.

[0003] However, to translate the potential of terahertz technology into practical applications, a wide variety of terahertz devices and systems are needed. Among these, the precise manipulation of the polarization state of terahertz waves is a crucial core element, especially the generation and control of linearly polarized terahertz waves, which has particularly significant applications in the terahertz field. For example, for anisotropic target objects, illumination with linearly polarized light can improve imaging contrast and the dimensionality of detected information; terahertz devices based on linear polarization filtering can be used to construct routing, filtering, and signal processing units in terahertz communication systems.

[0004] Meanwhile, in the complex channel propagation environment of terahertz communication, precise linear polarization control helps to suppress multipath interference and inter-channel crosstalk. By performing different polarization rotations on signals from different paths at the transmitter, the receiver can better separate and recover the target signal by precisely matching the linear polarization state of the transmitter, thereby improving the stability and reliability of the communication link.

[0005] Currently, the most commonly used method for generating linearly polarized terahertz waves is the terahertz metal wire grating. This method employs parallel metal wires to selectively transmit terahertz waves perpendicular to the wires and selectively reflect incident light with a polarization state parallel to the wires. While terahertz metal wire gratings can generate high-purity linearly polarized terahertz light over a wide bandwidth, they suffer from the following problems: (1) Difficult to integrate. Commercial wire grid terahertz polarizers are usually freestanding structures, made by fixing unsupported metal wires on a circular frame. They have low integration and are difficult to be compatible with existing semiconductor devices, which limits their application in next-generation miniaturized and ultra-integrated photonic systems.

[0006] (2) Limited functionality. Commercially available linear grating terahertz polarizers only have the function of generating linear polarization. If users need to achieve functions such as beam deflection, focusing, or vortex wave generation, they must cascade corresponding gratings, lenses, and Q-plates after the polarizer. This not only introduces additional insertion loss but also increases the system size.

[0007] (3) Real-time dynamic amplitude control is not possible. Traditional metal wire grids do not have amplitude control capabilities, and users must use additional attenuators to achieve this. Additional attenuators not only increase the system size but also easily cause beam deflection, reducing the reliability of the system. Summary of the Invention

[0008] The purpose of this invention is to provide an amplitude-tunable terahertz metasurface polarization selector and its usage method, solving the problems mentioned in the background art such as the difficulty in integrating terahertz linear grating polarizers, their limited functionality, and the inability to achieve real-time dynamic amplitude control.

[0009] To address the challenge of integration, this invention employs an all-dielectric silicon metasurface and monolithic structure compatible with existing semiconductor processes, enabling arbitrary linear polarization-selective metasurface devices. Specifically, the basic unit of the dielectric silicon pillar microstructure utilizes an interference design of isotropic and anisotropic silicon pillar units. By rotating the anisotropic silicon pillar units, selective transmission of arbitrary linearly polarized light is achieved.

[0010] To address the limitation of traditional wire-grid polarizers in terms of functionality, this invention introduces phase modulation into the basic unit of a terahertz metasurface polarization selector. By adjusting the geometry of the basic unit of the dielectric silicon pillar microstructure, continuous phase modulation within the 0-2π range is achieved simultaneously with polarization selection. Through the rational arrangement of these basic units of the dielectric silicon pillar microstructure, wavefront modulation functionality is embedded in the polarization selection layer, allowing for the synchronous output of terahertz waves with specified polarization states and wavefront shapes using a single polarization-selective metasurface.

[0011] To address the issue of the inability to achieve real-time dynamic amplitude control, this invention integrates a liquid crystal layer on the back side of a polarization-selective metasurface. A silicon dioxide encapsulation layer is located above and below the liquid crystal layer, and a graphite electrode layer lies between the silicon dioxide layer and the liquid crystal layer. When a driving voltage is applied between the upper and lower graphite electrodes, continuous adjustment of the transmission amplitude can be achieved.

[0012] To achieve the above objectives, the present invention provides an amplitude-tunable terahertz metasurface polarization selector, comprising a dielectric silicon substrate, a dielectric silicon pillar microstructure basic unit array disposed on the surface of the dielectric silicon substrate, and a liquid crystal layer applied to the back side of the dielectric silicon substrate. The basic unit of the dielectric silicon pillar microstructure consists of two silicon pillar unit structures, one isotropic and one anisotropic, and a dielectric silicon substrate.

[0013] Preferably, the dielectric silicon substrate layer is made of silicon and has a thickness of 500-2000 μm.

[0014] Preferably, the surface of the dielectric silicon substrate where the basic unit of the dielectric silicon pillar microstructure is located is the functional surface of the device, and the back surface of the dielectric silicon substrate is an optically flat surface; Set the target operating wavelength The basic unit of the dielectric silicon pillar microstructure has a period less than or equal to the x-axis. The period in the y-axis direction is less than or equal to .

[0015] Preferably, both the isotropic and anisotropic silicon pillar units are subwavelength structures, and the unit structure size is smaller than the operating wavelength of the incident target. ; Isotropic and anisotropic silicon pillar units are uniformly and equidistantly arranged with a spacing of 0.6. Up to 0.5 ; The isotropic silicon pillar units and the anisotropic silicon pillar units have the same height, which is 0.6. Up to 0.8 The cross-section of the silicon pillar unit accounts for 16%-21% of the cross-section of the basic unit of the dielectric silicon pillar microstructure.

[0016] Preferably, the anisotropic silicon pillar unit is a half-wave plate phase unit, and its phase delay along the fast axis is equal to that of the isotropic silicon pillar unit. Anisotropic silicon pillar units rotate around their geometric central axis by a corresponding angle depending on the selected polarization direction of transmission.

[0017] Preferably, there is a silicon dioxide encapsulation layer on the top and bottom of the liquid crystal layer, and a graphite electrode layer between the silicon dioxide layer and the liquid crystal layer. The thickness of the liquid crystal layer is the target operating wavelength divided by twice the refractive index difference between the long and short axes of the liquid crystal.

[0018] Preferably, a liquid crystal layer is introduced at the bottom of the dielectric silicon substrate to realize the active tuning function of the device.

[0019] A method for using an amplitude-tunable terahertz metasurface polarization selector includes the following: (1) When the incident light is incident on the terahertz metasurface polarization selector, the transmission dichroism of the terahertz wave with the linear polarization state and the orthogonal polarization state at any angle can be realized by adjusting the rotation angle of the anisotropic silicon pillar unit. (2) When the incident light is incident on the terahertz metasurface polarization selector from the front and back respectively, the polarization state selection of the transmitted terahertz wave is different due to the different equivalent rotation angles of the anisotropic silicon pillar units, resulting in asymmetric transmission. (3) A liquid crystal layer is introduced at the bottom of the dielectric silicon substrate to act as a polarization controller in order to realize the active tuning function of the device; In the initial state, a constant magnetic field is applied to the liquid crystal along the x-axis to anchor the liquid crystal molecules. By changing the external driving electric field along the z-axis, the optical axis of the liquid crystal molecules is rotated in the xz plane. (4) By changing the geometric parameters of the isotropic silicon pillar units and anisotropic silicon pillar units that make up the basic unit of the dielectric silicon pillar microstructure, the transmission phase response of the metasurface is controlled so that the phase response of the transmitted polarization covers the range of 0-2π; by arranging the basic unit of the dielectric silicon pillar microstructure, arbitrary wavefront shaping function is integrated in the metasurface.

[0020] Preferably, at the center operating frequency At this location, the anisotropic silicon pillar unit applies different phase responses to the incident terahertz wave along its fast and slow axes. Through the interference effect with the response of the isotropic silicon pillar unit, the metasurface causes the incident terahertz wave polarized along the fast axis of the anisotropic silicon pillar unit to be added in phase, and the terahertz wave is transmitted; while the terahertz wave orthogonal to it is canceled out in phase, and the terahertz wave cannot be transmitted; by adjusting the rotation angle of the anisotropic silicon pillar unit, the selection of terahertz waves with arbitrary linear polarization can be achieved.

[0021] Preferably, the asymmetric transport coefficient is defined as the ratio of the polarization direction of the metasurface. Forward transmission coefficient of linearly polarized terahertz waves and reverse transmission coefficient The relative differences are shown below: ; in, For asymmetric transmission coefficients.

[0022] Therefore, the present invention employs the above-mentioned asymmetric transmission terahertz metasurface polarization selector and its usage method, and the beneficial effects are as follows: (1) The present invention designs a terahertz metasurface polarization selector composed of isotropic silicon pillar units and anisotropic silicon pillar units. When the terahertz wave propagates perpendicular to the metasurface in the forward direction, a polarization extinction ratio of 0.78 is achieved at a frequency of 1 THz, and the transmission coefficient is 0.65. When the terahertz wave propagates perpendicular to the metasurface in the reverse direction, a polarization extinction ratio of 0.80 is achieved at a frequency of 1 THz, and the transmission coefficient is 0.64.

[0023] (2) The terahertz metasurface polarization selector of the present invention has asymmetric transmission characteristics for linearly polarized light when the terahertz wave propagates in the forward and reverse directions. In particular, when the anisotropic silicon pillar unit is rotated by 45° / 135°, the asymmetric transmission coefficient is as high as 0.79 at the center operating frequency of 1.0THz.

[0024] (3) The present invention also introduces liquid crystal to realize the dynamic amplitude tuning function of metasurface; and introduces gradient phase design to realize the wavefront shaping function of metasurface.

[0025] (4) The terahertz metasurface polarization selector of the present invention has a simple structure and is easy to process, and has potential application value in fields such as non-destructive testing, biomedical imaging, security inspection, and ultra-high-speed large-capacity wireless communication.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a three-dimensional structural schematic diagram of an amplitude-tunable terahertz metasurface polarization selector according to the present invention. Figure 2 This is a schematic diagram of the structure of the anisotropic silicon pillar unit in Embodiment 1 of the present invention when the terahertz wave propagates perpendicularly to the metasurface in the positive direction; wherein, (a) is a three-dimensional structure diagram; (b) is a two-dimensional structure diagram; Figure 3 This is a transmission coefficient diagram of terahertz waves propagating perpendicularly to the metasurface in the positive direction when the anisotropic silicon pillar unit is rotated by 45° in Embodiment 1 of the present invention. Figure 4 This is a diagram showing the transmission coefficient of a terahertz metasurface polarization selector for linearly polarized terahertz waves at different polarization angles when the terahertz wave propagates in the forward direction under the condition that the anisotropic silicon pillar unit is rotated by 45° in Embodiment 1 of the present invention, at a working frequency of 1THz. Figure 5 This is a schematic diagram of the asymmetric propagation phenomenon of terahertz waves when propagating perpendicularly to the metasurface in the forward and reverse directions when the anisotropic silicon pillar unit is rotated by 45° in Embodiment 2 of the present invention. Figure 6 This is a graph showing the variation of the asymmetric transmission coefficient of the metasurface with the rotation angle of the anisotropic silicon pillar unit during the propagation of a 45° linearly polarized terahertz wave in Embodiment 2 of the present invention. Figure 7 This is a graph showing the change in the transmission coefficient of a terahertz wave with a 45° polarized incident liquid crystal rotation angle when the anisotropic silicon pillar unit is rotated by 45° and the terahertz wave propagates in the forward direction. Figure 8 This is a graph showing the change of the terahertz wave transmission coefficient with the liquid crystal rotation angle at a working frequency of 1THz when the terahertz wave propagates in the forward direction under the condition that the anisotropic silicon pillar unit is rotated by 45° in Embodiment 3 of the present invention. Figure 9 This is a structural diagram of the basic unit of the eight groups of dielectric silicon pillar microstructures with 8th-order phase wavefront modulation when the anisotropic silicon pillar unit is rotated by 45° in Embodiment 4 of the present invention; wherein, (a) is a two-dimensional diagram of the eight groups of dielectric silicon pillar microstructures; and (b) is a three-dimensional structural diagram. Figure 10This is a diagram showing the transmission coefficient and phase response of eight groups of dielectric silicon pillar microstructure basic units with 8th-order phase wavefront modulation to linearly polarized waves at 45° and 135° when the anisotropic silicon pillar unit is rotated by 45° and the terahertz wave propagates in the forward direction.

[0028] Figure 11 This is a diagram showing the beam deflection effect of a terahertz deflector obtained by an 8th-order linear phase arrangement when the anisotropic silicon pillar unit is rotated by 45° in Embodiment 4 of the present invention, during the forward propagation of linearly polarized terahertz waves at 45° and 135°; where (a) is t 45,45 (a) shows the beam deflection effect; (b) shows the effect of t. 135,45 The beam deflection effect diagram; (c) is t 45,135 The beam deflection effect diagram; (d) is t 135,135 The diagram shows the effect of beam deflection.

[0029] Figure Labels 1. Basic unit of dielectric silicon pillar microstructure; 2. Dielectric silicon substrate; 3. Isotropic silicon pillar unit; 4. Anisotropic silicon pillar unit; 5. Terahertz wave with 45° polarization propagating in the forward direction when the anisotropic silicon pillar unit is rotated 45°; 6. Terahertz wave with 135° polarization propagating in the forward direction when the anisotropic silicon pillar unit is rotated 45°; 7. Liquid crystal layer; 8. Silicon dioxide encapsulation layer; 9. Graphite electrode layer. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] like Figure 1 As shown, the present invention discloses an amplitude-tunable terahertz metasurface polarization selector, comprising a dielectric silicon substrate 2, an array of dielectric silicon pillar microstructure basic units 1 disposed on the surface of the dielectric silicon substrate 2, and a liquid crystal layer 7 added to the back side of the dielectric silicon substrate; the dielectric silicon pillar microstructure basic unit 1 is composed of two silicon pillar unit structures, an isotropic silicon pillar unit 3 and an anisotropic silicon pillar unit 4, and the dielectric silicon substrate 2.

[0032] The dielectric silicon substrate 2 is made of silicon and has a thickness of 500-2000 μm. The surface of the dielectric silicon substrate 2, where the basic unit 1 of the dielectric silicon pillar microstructure is located, is the functional surface of the device, while the back surface of the dielectric silicon substrate 2 is an optically flat surface. Let the target operating wavelength be... The basic unit 1 of the dielectric silicon pillar microstructure has a period less than or equal to the x-axis. The period in the y-axis direction is less than or equal to .

[0033] Both the isotropic silicon pillar unit 3 and the anisotropic silicon pillar unit 4 are subwavelength structures, with unit structure dimensions smaller than the operating wavelength of the incident target. Preferably, the unit size is less than or equal to half a wavelength. .

[0034] Isotropic silicon pillar units 3 and anisotropic silicon pillar units 4 are uniformly and equidistantly arranged with a spacing of 0.6. Up to 0.5 The isotropic silicon pillar unit 3 and the anisotropic silicon pillar unit 4 have the same height, which is 0.6. Up to 0.8 The cross-section of the silicon pillar unit accounts for 16%-21% of the cross-section of the basic unit 1 of the dielectric silicon pillar microstructure.

[0035] The anisotropic silicon pillar unit 4 is a half-wave plate phase unit, and its phase delay along the fast axis is equal to that of the isotropic silicon pillar unit 3. The anisotropic silicon pillar unit 4 rotates around its geometric central axis by a corresponding angle according to the selected polarization direction of transmission.

[0036] A silicon dioxide encapsulation layer 8 is placed above and below the liquid crystal layer 7, and a graphite electrode layer 9 is placed between the silicon dioxide encapsulation layer 8 and the liquid crystal layer 7. The thickness of the liquid crystal layer 7 is the target operating wavelength divided by twice the refractive index difference between the long and short axes of the liquid crystal. The liquid crystal layer 7, introduced at the bottom of the dielectric silicon substrate 2, is used to realize the active tuning function of the device.

[0037] Based on this, the present invention provides a method for using an amplitude-tunable terahertz metasurface polarization selector, comprising the following: (1) When the incident light is incident on the terahertz metasurface polarization selector, the transmission dichroism of the terahertz wave with the linear polarization state and the orthogonal polarization state at any angle can be realized by adjusting the rotation angle of the anisotropic silicon pillar unit.

[0038] At the center operating frequency At this location, anisotropic silicon pillar units apply different phase responses to incident terahertz waves along their fast and slow axes. Through interference with the responses of isotropic silicon pillar units, the metasurface causes terahertz waves polarized along the fast axis of the anisotropic silicon pillar units to add in phase, allowing the terahertz waves to pass through; however, terahertz waves orthogonal to the anisotropic silicon pillar units are destructively phased, preventing their passage. By adjusting the rotation angle of the anisotropic silicon pillar units, the selection of terahertz waves with arbitrary linear polarization can be achieved.

[0039] (2) When the incident light is incident on the terahertz metasurface polarization selector from the front and back respectively, the polarization state selection of the transmitted terahertz wave is also different due to the different equivalent rotation angles of the anisotropic silicon pillar units.

[0040] (3) A liquid crystal layer is introduced at the bottom of the dielectric silicon substrate to act as a polarization controller, so as to realize the active tuning function of the device. In the initial state, a constant magnetic field is applied to the liquid crystal along the x-axis to anchor the liquid crystal molecules. By changing the external driving electric field along the z-axis, the optical axis of the liquid crystal molecules is rotated in the xz plane.

[0041] (4) By changing the geometric parameters of the isotropic silicon pillar units and anisotropic silicon pillar units that make up the basic unit of the dielectric silicon pillar microstructure, the transmission phase response of the metasurface is controlled so that the phase response of the transmitted polarization covers the range of 0-2π; by arranging the basic unit of the dielectric silicon pillar microstructure in a reasonable manner, arbitrary wavefront shaping function is integrated in the metasurface.

[0042] Example 1 like Figure 2 As shown, the basic unit of the dielectric silicon pillar microstructure consists of two silicon pillar unit structures: an isotropic silicon pillar unit and an anisotropic silicon pillar unit, and a dielectric silicon substrate. The isotropic silicon pillar unit is located in the upper half of the basic unit of the dielectric silicon pillar microstructure; the anisotropic silicon pillar unit is located in the lower half of the basic unit of the dielectric silicon pillar microstructure after being rotated about its central axis by a corresponding angle.

[0043] like Figure 3 As shown, let the rotation angle of the anisotropic silicon pillar unit be... When the angle is 45°, the propagation of terahertz waves perpendicular to the metasurface in the forward direction depends on the interference design of isotropic silicon pillar units and anisotropic silicon pillar units rotated 45°. The center operating frequency of the terahertz metasurface polarization-selective device... =1.0THz (target operating wavelength) =300μm), allowing 45° linearly polarized terahertz waves to pass through the metasurface with a transmission coefficient of 0.65, while the transmission coefficient of terahertz waves with orthogonal polarization is less than 0.1, thus achieving polarization selectivity for 45° linearly polarized waves.

[0044] Specifically, the basic unit of the dielectric silicon pillar microstructure includes an isotropic silicon pillar unit and an anisotropic silicon pillar unit, with the rotation angle of the anisotropic silicon pillar unit changed to 45°. When the terahertz wave propagates perpendicularly to the metasurface in the forward direction, the isotropic and anisotropic silicon pillar units provide the same relative phase for the 45° linearly polarized wave, resulting in the 45° linearly polarized waves being superimposed in phase after the terahertz wave is transmitted. However, for the 135° linearly polarized terahertz wave, the isotropic and anisotropic silicon pillar units provide a relative π phase delay, resulting in the 135° linearly polarized waves being out of phase and canceling each other out after the terahertz wave is transmitted, achieving a selective transmission effect for the 45° linearly polarized wave. Figure 4 The transmission coefficient of linearly polarized terahertz waves at different polarization angles is given when the terahertz wave propagates perpendicularly to the metasurface at a working frequency of 1 THz.

[0045] When terahertz waves propagate perpendicularly to the metasurface in the positive direction, A polarization extinction ratio of 0.78 was achieved at a frequency of 1.0 THz, while the transmission coefficient was 0.65; when the terahertz wave propagates in the opposite direction perpendicular to the metasurface, at A polarization extinction ratio of 0.80 was achieved at a frequency of 1.0 THz, while the transmittance was 0.64.

[0046] Polarization extinction ratio The calculation formula is: ; in, Transmission coefficient representing the polarization state of the target; The transmittance coefficient represents the polarization state orthogonal to the target polarization state.

[0047] Example 2 When terahertz waves propagate forward (from the dielectric silicon substrate to the dielectric silicon pillar microstructure basic unit array layer) and backward (from the dielectric silicon pillar microstructure basic unit array layer to the dielectric silicon substrate) in a vertical metasurface polarization selection device, the polarization state of the terahertz waves selected for transmission by the terahertz metasurface polarization selection device is different.

[0048] The rotation angle of the anisotropic silicon pillar unit, i.e., the rotation angle of the fast axis, is set as... Let the angle between the polarization direction of the incident linearly polarized terahertz wave and the x-axis be denoted as At this point, the metasurface is polarized in the following directions. The linearly polarized terahertz wave has the highest transmission coefficient for the polarization direction. The linearly polarized terahertz wave has the lowest transmission coefficient. For a polarization direction of... For a linearly polarized terahertz light source, when the terahertz wave propagates in the reverse direction, its equivalent linear polarization direction becomes... .

[0049] Therefore, under normal circumstances, linearly polarized terahertz waves of the same polarization state have different propagation coefficients in the forward and reverse directions, exhibiting asymmetric propagation. The asymmetric propagation coefficient is defined as the ratio of the propagation coefficient of the metasurface to the polarization direction. Forward transmission coefficient of linearly polarized terahertz waves and reverse transmission coefficient The relative differences are shown below: ; Specifically, when the rotation angle of the anisotropic silicon pillar unit is 45° and 135°, such as Figure 5The terahertz metasurface polarization selector shown has the largest asymmetric transmission coefficient of 0.79, and the asymmetric transmission effect is the most obvious. When the rotation angle of the anisotropic silicon pillar unit is 0° and 90°, the asymmetric transmission coefficient of the terahertz metasurface polarization selector is 0, and the metasurface does not have the asymmetric transmission function at this time. Figure 6 Rotation angle of anisotropic silicon pillar unit The change in the asymmetric transport coefficient of the metasurface during the change.

[0050] Example 3 To achieve real-time dynamic amplitude control, a liquid crystal layer is cascaded on the dielectric silicon substrate of the terahertz metasurface polarization selector. The liquid crystal layer acts as a polarization controller. There is a layer of silicon dioxide above and below the liquid crystal layer, and a graphite electrode layer between the silicon dioxide layer and the liquid crystal layer.

[0051] Initially, a constant magnetic field is applied along the x-axis of the liquid crystal to anchor the liquid crystal molecules. By changing the external driving electric field along the z-axis, the orientation of the liquid crystal molecules rotates in the xz-plane. When the driving voltage is higher than a threshold, the liquid crystal molecules are driven by the external electric field along the z-axis. As the driving voltage decreases, the liquid crystal molecules gradually move back to the xy-plane along the magnetic field direction, reaching an intermediate state. This displacement of the liquid crystal molecule orientation leads to the modulation of the intensity of light transmitted through the layer.

[0052] Taking the rotation of an anisotropic silicon pillar unit by 45° as an example, when the driving voltage is higher than the threshold, the liquid crystal molecules are driven by the external electric field along the z-axis, rotating from 0° to 90°. The polarization state output by the liquid crystal layer gradually changes from 45° to 135° in the xy plane. Since the dielectric microstructure array layer can only selectively transmit the 45° polarization state, the output amplitude of the transmitted wave gradually changes from 0 to its maximum through the electrically controlled rotation of the liquid crystal molecules. As the driving voltage decreases, the liquid crystal molecules gradually move back to the xy plane along the magnetic field direction, reaching an intermediate state.

[0053] When a terahertz wave propagates perpendicularly to the metasurface in the positive direction, under high voltage, the polarization direction of the 45° linearly polarized wave remains unchanged due to the isotropic response of the liquid crystal layer; however, without external electric drive, the polarization direction of the 45° linearly polarized wave will rotate by 90° when it passes through the liquid crystal layer.

[0054] When a terahertz wave propagates perpendicularly to the metasurface in the positive direction, the transmission coefficient of the terahertz wave polarized at 45° changes with the rotation angle of the liquid crystal, as follows: Figure 7 As shown. At a working frequency of 1 THz, when a terahertz wave propagates perpendicularly to the metasurface in the forward direction, the transmission coefficient of the terahertz wave polarized at 45° changes with the rotation angle of the liquid crystal, as shown below. Figure 8 As shown.

[0055] Example 4 The transmission phase response of the metasurface can be controlled by changing the geometric parameters of the isotropic and anisotropic silicon pillar units that make up the basic unit of the dielectric silicon pillar microstructure.

[0056] Assuming the wavefront shaping phase discretization order is 8, eight sets of basic units of dielectric silicon pillar microstructures with different size parameters are selected, with relative phase responses of 0, π / 4, π / 2, 3π / 4, π, 5π / 4, 3π / 2, and 7π / 4, respectively. Figure 9 As shown. The phase response covers the range of 0-2π. By arranging eight different-sized supercell structures in different ways, beam deflection, beam focusing, and other beam-shaping functions can be integrated into the metasurface. The transmission coefficient and phase response of the eight groups of dielectric silicon pillar microstructure basic units with 8th-order phase wavefront modulation for 45° and 135° linearly polarized waves are shown in the figure. Figure 10 As shown.

[0057] For example, by arranging eight different structures sequentially laterally along the x-direction, with their phases increasing linearly, a discretized linear phase ramp can be formed, enabling the selection and beam deflection of terahertz waves in specific linearly polarized states. The beam deflection effect of the terahertz deflector on the forward propagation of linearly polarized terahertz waves at 45° and 135° is shown in the figure. Figure 11 As shown.

[0058] Therefore, this invention employs an amplitude-tunable terahertz metasurface polarization selector and its application method, utilizing a two-atom interference design to achieve transparency for linearly polarized terahertz waves at a specific angle, while simultaneously blocking perpendicularly polarized terahertz waves. It exhibits different transmission characteristics for terahertz waves of the same polarization state incident in both forward and reverse directions, demonstrating asymmetric transmission capabilities. Furthermore, liquid crystal is introduced to achieve dynamic tuning of the metasurface. This terahertz metasurface polarization selector has a simple structure, is easy to fabricate, and can be widely applied in terahertz communication, imaging, and sensing fields, providing a new approach for the design of active terahertz polarization selection devices.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An amplitude-tunable terahertz metasurface polarization selector, characterized in that: It includes a dielectric silicon substrate, a basic unit array of dielectric silicon pillar microstructures disposed on the surface of the dielectric silicon substrate, and a liquid crystal layer added to the back side of the dielectric silicon substrate; The basic unit of the dielectric silicon pillar microstructure consists of two silicon pillar unit structures, one isotropic and one anisotropic, and a dielectric silicon substrate.

2. The amplitude-tunable terahertz metasurface polarization selector according to claim 1, characterized in that: The dielectric silicon substrate is made of silicon and has a thickness of 500-2000 μm.

3. The amplitude-tunable terahertz metasurface polarization selector according to claim 2, characterized in that: The surface of the dielectric silicon substrate on which the basic unit of the dielectric silicon pillar microstructure is located is the functional surface of the device, and the back side of the dielectric silicon substrate is the optically flat surface. Set the target operating wavelength The basic unit of the dielectric silicon pillar microstructure has a period less than or equal to the x-axis. The period in the y-axis direction is less than or equal to .

4. The amplitude-tunable terahertz metasurface polarization selector according to claim 1, characterized in that: Both isotropic and anisotropic silicon pillar units are subwavelength structures, with unit cell dimensions smaller than the operating wavelength of the incident target. ; Isotropic and anisotropic silicon pillar units are uniformly and equidistantly arranged with a spacing of 0.

6. Up to 0.5 ; The isotropic silicon pillar units and the anisotropic silicon pillar units have the same height, which is 0.

6. Up to 0.8 The cross-section of the silicon pillar unit accounts for 16%-21% of the cross-section of the basic unit of the dielectric silicon pillar microstructure.

5. The amplitude-tunable terahertz metasurface polarization selector according to claim 4, characterized in that: Anisotropic silicon pillar units are half-wave plate phase units, and their phase delay along the fast axis is equal to that of isotropic silicon pillar units. Anisotropic silicon pillar units rotate around their geometric central axis by a corresponding angle depending on the selected polarization direction of transmission.

6. The amplitude-tunable terahertz metasurface polarization selector according to claim 1, characterized in that: There is a silicon dioxide encapsulation layer on the top and bottom of the liquid crystal layer, and a graphite electrode layer between the silicon dioxide layer and the liquid crystal layer. The thickness of the liquid crystal layer is the target operating wavelength divided by twice the refractive index difference between the long and short axes of the liquid crystal.

7. The amplitude-tunable terahertz metasurface polarization selector according to claim 6, characterized in that: A liquid crystal layer is introduced at the bottom of a dielectric silicon substrate to enable the active tuning function of the device.

8. A method of using an amplitude-tunable terahertz metasurface polarization selector according to any one of claims 1-7, characterized in that, Includes the following: (1) When the incident light is incident on the terahertz metasurface polarization selector, the transmission dichroism of the terahertz wave with the linear polarization state and the orthogonal polarization state at any angle can be realized by adjusting the rotation angle of the anisotropic silicon pillar unit. (2) When the incident light is incident on the terahertz metasurface polarization selector from the front and back respectively, the polarization state selection of the transmitted terahertz wave is different due to the different equivalent rotation angles of the anisotropic silicon pillar units, resulting in asymmetric transmission. (3) A liquid crystal layer is introduced at the bottom of the dielectric silicon substrate to act as a polarization controller in order to realize the active tuning function of the device; In the initial state, a constant magnetic field is applied to the liquid crystal along the x-axis to anchor the liquid crystal molecules. By changing the external driving electric field along the z-axis, the optical axis of the liquid crystal molecules is rotated in the xz plane. (4) By changing the geometric parameters of the isotropic silicon pillar units and anisotropic silicon pillar units that make up the basic unit of the dielectric silicon pillar microstructure, the transmission phase response of the metasurface is controlled so that the phase response of the transmitted polarization covers the range of 0-2π; by arranging the basic unit of the dielectric silicon pillar microstructure, arbitrary wavefront shaping function is integrated in the metasurface.

9. A method of using an amplitude-tunable terahertz metasurface polarization selector according to claim 8, characterized in that, At the center operating frequency At this location, the anisotropic silicon pillar unit applies different phase responses to the incident terahertz wave along its fast and slow axes. Through the interference effect with the response of the isotropic silicon pillar unit, the metasurface causes the incident terahertz wave polarized along the fast axis of the anisotropic silicon pillar unit to be added in phase, and the terahertz wave is transmitted; while the terahertz wave orthogonal to it is canceled out in phase, and the terahertz wave cannot be transmitted; by adjusting the rotation angle of the anisotropic silicon pillar unit, the selection of terahertz waves with arbitrary linear polarization can be achieved.

10. A method of using an amplitude-tunable terahertz metasurface polarization selector according to claim 9, characterized in that, The asymmetric transport coefficient is defined as the ratio of the polarization direction of the metasurface. Forward transmission coefficient of linearly polarized terahertz waves and reverse transmission coefficient The relative differences are shown below: ； in, For asymmetric transmission coefficients.

Images