Mode decoupled dynamic switching terahertz wave plate

Abstract

This invention discloses a mode-decoupled dynamically switching terahertz waveplate, belonging to the fields of terahertz technology and micro / nano photonic devices. The waveplate, from top to bottom, comprises a metal-vanadium dioxide composite metasurface, a quartz substrate, and a metal reflective layer. The metal-vanadium dioxide composite metasurface includes patterned metal and patterned vanadium dioxide. The patterned vanadium dioxide exhibits phase transition properties, enabling the waveplate to dynamically switch between two independent waveplate modes. These two independent waveplate modes are decoupled modes. The fast / slow axes and phase difference of these two independent waveplate modes can be independently controlled. The waveplate is used to achieve dynamic switching between arbitrary linearly polarized light fields and between arbitrary polarization states.

Description

Technical Field

[0001] This invention relates to the fields of terahertz technology and micro / nano photonic devices, and particularly to a mode-decoupled dynamically switching terahertz waveplate. Background Technology

[0002] A terahertz waveplate is a flat plate made of birefringent material. It alters the polarization state of radiation by shifting the phase between the two perpendicularly polarized components of a wave. This phase shift allows the waveplate to change the polarization direction of linearly polarized light, or convert linearly polarized light into circularly polarized light, and vice versa. Based on the phase delay, terahertz waveplates can be divided into half-wave plates (λ / 2 plates) and quarter-wave plates (λ / 4 plates). A half-wave plate provides a phase delay of π, enabling it to change the polarization direction of linearly polarized light; while a quarter-wave plate provides a phase delay of π / 2, enabling it to convert linearly polarized light into circularly or elliptically polarized light. Terahertz waveplates have enormous application value and development potential in sensing, imaging, and communication fields.

[0003] Traditional methods based on birefringence and Faraday magneto-optical effects typically require thick crystal materials, making integration into existing optical systems difficult. Furthermore, the lack of natural materials with strong terahertz photoelectric responses results in a limited number of terahertz waveplates with poor performance, gradually becoming a bottleneck restricting terahertz applications. In recent years, artificial metasurfaces have attracted widespread attention due to their advantages of being ultrathin, easy to integrate, and flexible in design. Metasurfaces are two-dimensional planar metamaterials composed of subwavelength arrays, capable of achieving special functions not found in natural materials. By designing anisotropic patterns of metallic or dielectric materials, the amplitude and phase of two orthogonal polarization components can be modulated to different degrees, thereby achieving polarization state conversion. However, the polarization conversion characteristics of such devices can only be manipulated by adjusting the geometric parameters of the structure, and cannot be changed once fabricated. MEMS-based mechanical manipulation methods typically require advanced fabrication techniques. The discovery of tunable materials such as vanadium dioxide, graphene, and black phosphorus has provided new ideas for the dynamic control of terahertz waveplates. However, the fast / slow axes and phase difference of terahertz waveplates based on tunable materials cannot be independently controlled in different operating modes. When structural parameters are adjusted to control the fast / slow axis and phase difference in a certain mode, the fast / slow axis and phase difference in other modes will also change accordingly, which severely limits the functions that the device can achieve. Therefore, constructing a dynamically switching terahertz waveplate with mode decoupling has become an urgent technical problem to be solved at this stage. Summary of the Invention

[0004] Based on the technical problems to be solved by the present invention, the present invention proposes a mode-decoupled dynamically switched terahertz waveplate. The terahertz waveplate described in this invention is a tunable mode-decoupled dynamically switched terahertz waveplate based on vanadium dioxide. The device utilizes the tunable phase transition characteristics of vanadium dioxide's conductivity under external stimuli such as heat, electricity, and light to regulate the resonance characteristics of the metal-vanadium dioxide composite metasurface, making it exhibit optical axis decoupling characteristics, thereby constructing a mode-decoupled dynamically switched terahertz waveplate.

[0005] This invention provides a mode-decoupled dynamically switching terahertz waveplate, comprising, from top to bottom, a metal-vanadium dioxide composite metasurface, a quartz substrate, and a metal reflective layer; the metal-vanadium dioxide composite metasurface includes patterned metal and patterned vanadium dioxide; the patterned vanadium dioxide exhibits phase transition characteristics, enabling the waveplate to dynamically switch between two independent waveplate modes; these two independent waveplate modes are decoupled modes; the fast / slow axes and phase difference of these two independent waveplate modes can be independently controlled; the waveplate is used to achieve dynamic switching between arbitrary linearly polarized light fields; and the waveplate is used to achieve dynamic switching between arbitrary polarization states. The quartz substrate is a growth substrate for vanadium dioxide thin films.

[0006] Furthermore, the metal-vanadium dioxide composite metasurface includes an array unit; the array unit includes a metal C-SRR (C-shaped split ring resonator) and patterned vanadium dioxide; the patterned vanadium dioxide fills the gaps in the metal C-SRR and extends into a rectangular antenna.

[0007] Furthermore, the phase transition characteristics of the patterned vanadium dioxide are the characteristics of the patterned vanadium dioxide transitioning between an insulating phase and a metallic phase under the action of external stimuli such as heat, electricity, and light; the fast / slow axis of the waveplate in the insulating phase is along the angle bisector of the notch of the metal C-SRR; the fast / slow axis of the waveplate in the metallic phase is along the long side of the antenna; the fast / slow axis directions of the waveplate in the insulating phase and the metallic phase can be arbitrarily selected within the range of -90° to 90°.

[0008] Furthermore, the waveplate phase difference between the insulating phase and the metallic phase can be adjusted by the structural parameters of the array unit without changing the substrate thickness and array period; the waveplate phase difference between the insulating phase and the metallic C-SRR can be adjusted by the angle of the metallic C-SRR; the waveplate phase difference between the metallic phase and the metallic phase can be adjusted by the length of the antenna.

[0009] Furthermore, the mode decoupling characteristics of the waveplate originate from the generation or disappearance of electric dipole resonance and magnetic dipole resonance in the metal-vanadium dioxide composite metasurface caused by the phase transition of the patterned vanadium dioxide.

[0010] Furthermore, by selecting different structural parameters of the metal-vanadium dioxide composite metasurface, the waveplate can achieve dynamic switching between quarter-wave plates, quarter-wave plates to half-wave plates, half-wave plates to half-wave plates, or half-wave plates to quarter-wave plates near 350 GHz, with mode decoupling.

[0011] Furthermore, the waveplate includes device A, device B, device C, or device D; device A can achieve dynamic switching from a quarter-wave plate to a quarter-wave plate; device B can achieve dynamic switching from a quarter-wave plate to a half-wave plate; device C can achieve dynamic switching from a half-wave plate to a half-wave plate; device D can achieve dynamic switching from a half-wave plate to a quarter-wave plate; devices A, B, C, and D all have mode decoupling characteristics, that is, the fast / slow axis directions in the two operating modes can be independently adjusted.

[0012] Furthermore, the planar array constructed using the device A or the device C with different fast / slow axis directions as basic units can be used for dynamic switching between arbitrary linearly polarized light fields; the dynamic switching between arbitrary linearly polarized light fields includes dynamic switching between radially and tangentially polarized vortex beams, or dynamic switching between polarized vortex beams with different topological charges.

[0013] Furthermore, the waveplate phase difference between the insulating phase and the metallic phase can be independently adjusted by changing the angle and radius of the metallic C-SRR, and / or the length of the antenna; by combining the adjustment of the waveplate phase difference with the adjustment of the fast / slow axis direction of the waveplate, the device can achieve dynamic switching between arbitrary polarization states.

[0014] Furthermore, the waveplate has a MIM-like structure. This invention employs a metasurface-dielectric layer-metal reflective layer structure to improve the device's output efficiency. The metal reflective layer shields the transmission channel, eliminating transmission energy loss, and together with the quartz dielectric layer and the metal-vanadium dioxide composite metasurface, forms a metal-insulator-metal (MIM) sandwich cavity. The Fabry-Pérot (FP) interference effect induced by this cavity significantly improves the device's polarization conversion efficiency.

[0015] Furthermore, the waveplate is made of quartz as the dielectric cavity material. The growth of vanadium dioxide thin films requires high-temperature processes such as annealing. Compared to commonly used organic polymer dielectric layer materials (e.g., PI, Parylene) in the terahertz band, quartz is heat-resistant and suitable as a growth substrate for vanadium dioxide thin films.

[0016] Furthermore, the tunable material in the waveplate is not limited to vanadium dioxide; other tunable materials with a large conductivity adjustment range can also replace vanadium dioxide to achieve the same function.

[0017] Compared with existing technologies, this invention proposes a mode-decoupled dynamically switched terahertz waveplate, which has the following advantages:

[0018] 1. This invention proposes a metal-vanadium dioxide composite metasurface with optical axis decoupling, in which the optical axis direction in any state does not affect the resonance and transmission characteristics in another state.

[0019] 2. The mode-decoupled dynamic switching terahertz waveplate described in this invention allows for independent control of the fast / slow axes and phase difference in two operating modes. Without changing the substrate thickness and array period, the waveplate properties in the two operating modes can be independently controlled through the structural parameters of the array units, greatly expanding the functionality achievable by the device. Based on this, dynamic switching between arbitrary linearly polarized light fields and between arbitrary polarization states can be realized.

[0020] 3. The terahertz waveplate based on vanadium dioxide in this invention has strong stability and high efficiency. The conductivity of vanadium dioxide can be actively adjusted by thermal, electrical, and optical methods. At the same time, considering the high temperature required during the growth of vanadium dioxide thin film, this invention selects quartz as the dielectric cavity material to construct a dynamically switching terahertz waveplate that can be applied to practical mode decoupling. Attached Figure Description

[0021] Figure 1 The diagram shows an equivalent structure of a metal-vanadium dioxide composite metasurface according to an embodiment of the present invention, wherein Figure A is an equivalent structure diagram in the insulating state and Figure B is an equivalent structure diagram in the metallic state.

[0022] Figure 2 The diagram shows a schematic of a dynamically switched terahertz waveplate based on tunable mode decoupling of vanadium dioxide according to an embodiment of the present invention. In the diagram, Figure A is a perspective view of the device and Figure B is a top view of the metal-vanadium dioxide composite metasurface.

[0023] Figure 3This invention illustrates a schematic diagram of a method for dynamically switching between arbitrary linearly polarized light fields, wherein Figure A shows the relationship between the polarization direction of the linearly polarized light output by device A under left-handed circularly polarized light incident light and the angle bisector direction β1 of the C-SRR notch and the long side direction β2 of the antenna; Figure B shows a schematic diagram of a planar array constructed using devices A with different β1 and β2 as basic units to realize the dynamic switching between radially polarized vortices and tangentially polarized vortices.

[0024] Figure 4 This diagram illustrates a method for dynamically switching between arbitrary polarization states according to an embodiment of the present invention. Figure A shows the relationship between the phase difference in the insulating state and the angular size α of the C-SRR, and the relationship between the phase difference in the metallic state and the antenna length L. Figure B shows the amplitude ratio |E| of the output polarization state when x-polarized light is incident on the waveplate surface. ox | / |E oy | and phase difference Δφ xy The relationship between the fast / slow axis direction β and the phase difference δ of the waveplate is shown in Figure C, which shows the polarization state that can be obtained by scanning α and L with combination 2: R = 60 μm, r = 40 μm. Detailed Implementation

[0025] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0026] The present invention discloses a mode-decoupled dynamically switched terahertz waveplate. The main technical principle includes: utilizing the phase transition characteristics of vanadium dioxide to modulate the resonance characteristics of the metal-vanadium dioxide composite metasurface, so that its optical axes are decoupled in two states, thereby constructing a mode-decoupled dynamically switched terahertz waveplate. Please refer to [link to relevant documentation]. Figure 1 A. In the insulating state, vanadium dioxide acts as a dielectric, and its thickness is much smaller than the wavelength of a terahertz wave. This prevents it from generating resonance on its own and from affecting resonances generated by other materials. Therefore, the geometric parameters of the vanadium dioxide pattern (e.g., the long side direction β2 of the antenna) have negligible influence on the reflection characteristics of the device in the insulating state. In this case, the reflection characteristics of the device are determined by the resonance characteristics of the metallic C-SRR, which generates magnetic dipole resonance along the tangential direction of the notch. (See also...) Figure 1In the metallic state (B), vanadium dioxide is equivalent to a metal. The filling of the gap causes the magnetic dipole resonance to disappear, while the vanadium dioxide extending into a rectangular antenna excites electric dipole resonance along its long side. Ideally, vanadium dioxide can be considered a metal, and the metallic C-SRR degenerates into a closed metallic ring. Therefore, the orientation of the gap β1 has a negligible effect on the reflection characteristics of the device in the metallic state. Due to the symmetry of the equivalent structure, β1 and β2 can be regarded as the optical axis directions in the insulating and metallic states, respectively. Therefore, the optical axes (fast / slow axes) of the device are decoupled in the two states.

[0027] Based on the above principles, this invention proposes a mode-decoupled dynamically switching terahertz waveplate. The waveplate, from top to bottom, comprises a metal-vanadium dioxide composite metasurface, a quartz substrate, and a metal reflective layer. The metal-vanadium dioxide composite metasurface includes patterned metal and patterned vanadium dioxide. The patterned vanadium dioxide exhibits phase transition characteristics, enabling the waveplate to dynamically switch between two independent waveplate modes. These two independent waveplate modes are decoupled modes. The fast / slow axes and phase difference of these two independent waveplate modes can be independently controlled. The waveplate is used to achieve dynamic switching between arbitrary linearly polarized light fields and between arbitrary polarization states.

[0028] The metal-vanadium dioxide composite metasurface, quartz substrate, and metal reflective layer described in this invention constitute a Fabry-Perot cavity. The constructive interference effect within the cavity enhances the device's polarization conversion capability, significantly improving its polarization conversion efficiency. The vanadium dioxide thin film growth process requires high-temperature processes such as annealing. Compared to commonly used organic polymer dielectric layer materials (e.g., PI, Parylene) in the terahertz band, quartz is heat-resistant and suitable as a growth substrate for vanadium dioxide thin films. The metal reflective layer shields the transmission channel, eliminating transmission energy loss, and together with the quartz dielectric layer and the metal-vanadium dioxide composite metasurface, forms a metal-insulator-metal (MIM) sandwich cavity. The Fabry-Perot (FP) interference effect induced by this cavity significantly improves the device's polarization conversion efficiency.

[0029] Example 1

[0030] This invention proposes specific structural parameters and device performance of a dynamically switchable terahertz waveplate based on vanadium dioxide.

[0031] Please see Figure 2The thicknesses of the metal and vanadium dioxide are 200 nm and 300 nm, respectively, and the thickness of the quartz substrate is 100 μm. The period of the square array of the metal-vanadium dioxide composite metasurface is P = 300 μm. The outer and inner radii of the C-SRR are R and r, respectively, with an angle of α. The angle bisector of the notch makes an angle β1 with the x-axis. The length and width of the antenna are L and W = 50 μm, respectively, and the angle β2 makes an angle β2 with the x-axis.

[0032] Based on metal-vanadium dioxide composite metasurfaces with different structural parameters, four typical mode-decoupled dynamically switched terahertz waveplates were designed, achieving dynamic switching from quarter-wave plate to quarter-wave plate (device A), from quarter-wave plate to half-wave plate (device B), from half-wave plate to half-wave plate (device C), and from half-wave plate to quarter-wave plate (device D), respectively. All four devices exhibit mode-decoupling characteristics. The structural parameters of the four devices are shown in Table 1. The reflection amplitude and phase difference of the four devices under incident linearly polarized light polarized along the optical axis (fast / slow axis) are shown in Table 2, where u and v represent the optical axis direction in the insulating state, and u' and v' represent the optical axis direction in the metallic state. A phase difference of 90° indicates that it can be used as a quarter-wave plate, a phase difference of 180° indicates that it can be used as a half-wave plate, and a reflection amplitude greater than 0.8 indicates its high efficiency.

[0033] Table 1. List of structural parameters for the four devices

[0034]

[0035]

[0036] Table 2 lists the reflection amplitude and phase difference of four devices under incident linearly polarized light polarized along the optical axis (fast / slow axis).

[0037]

[0038] Example 2

[0039] This invention proposes a method for calculating the reflection characteristics of a waveplate.

[0040] The reflection characteristics of the waveplate were calculated using the RF module of COMSOL Multiphysics, based on the finite element method. To reduce the number of degrees of freedom and improve computational speed, periodic boundary conditions (in the x and y directions) were used to model the array elements. A perfectly matched layer was placed at the top of the model (z direction) to simulate an infinitely extending air domain. An ideal electrical conductor boundary condition was placed at the bottom of the model (z direction) to simulate a metallic reflective layer. A port was placed at the bottom (z direction) of the perfectly matched layer to add a light source and calculate the reflection coefficient. The COMSOL numerical simulation method described is an existing technique for studying the transport properties of metasurfaces.

[0041] The reflection characteristics of the waveplate can also be calculated using the transfer matrix method. The calculated reflection coefficient of the device under incident linearly polarized light polarized along the optical axis (fast / slow axis) (β1 and its orthogonal directions in the insulating state, β2 and its orthogonal directions in the metallic state) is:

[0042]

[0043] In the formula, r uu 、r′ uu t uu , t′ uu r vv 、r′ vv t vv , t′ vv Let Y be the reflection and transmission coefficients of the metal-vanadium dioxide composite metasurface under incident linearly polarized light polarized along the optical axis (fast / slow axis), where ∠ represents backpropagation, k₀ is the wave vector of the electromagnetic wave, and n and D are the refractive index and thickness of the quartz dielectric layer. Furthermore, the reflection and transmission coefficients can be expressed as the equivalent admittance Y of the metal-vanadium dioxide composite metasurface along the optical axis (fast / slow axis). u and Y v Connect

[0044] Equivalent admittance Y u and Y v The structure is determined by the metal-vanadium dioxide composite metasurface.

[0045] The polarization state of the reflected light from the waveplate under x-polarized incident light can be calculated using the Jones vector and matrix. The calculated Jones vector of the reflected light is:

[0046]

[0047] In the formula, A = |r1| and B = |r2| are the reflection amplitudes along the optical axis (fast / slow axis), δ = arg(r1) - arg(r2) is the waveplate phase difference, and β is the direction of the optical axis (fast / slow axis). The Stokes parameters of the polarization state of the reflected light are:

[0048]

[0049] In the formula, This represents the phase difference between the x and y components.

[0050] Example 3

[0051] This invention proposes an application of a vanadium dioxide-based tunable dynamically switching terahertz waveplate in the dynamic switching between arbitrary linearly polarized optical fields.

[0052] Devices A and C in Example 1 can be used to achieve dynamic switching between arbitrary linearly polarized light fields. Taking device A as an example, let a beam of left-handed circularly polarized light be incident on the surface of device A (or let x-polarized light be incident on the surface of device C). Since device A is equivalent to a quarter-wave plate in the insulating and metallic states, the reflected light is linearly polarized light, and the polarization direction depends on the optical axis (fast / slow axis) direction (β1 and β2) in the two states. Figure 3 A shows the polarization direction of the linearly polarized light output by the device under different C-SRR notch angle bisector direction β1 and antenna long side direction β2. The blue double-headed arrows represent the polarization direction in the insulating state, and the red double-headed arrows represent the polarization direction in the metallic state. According to the properties of a quarter-wave plate, the polarization direction forms a 45° angle with the optical axis. However, since the reflection amplitude ratios in the fast and slow axis directions are not strictly equal and the phase difference is not strictly equal to 90°, the actual polarization direction will have a slight deviation. Even so, the polarization direction can still be arbitrarily selected within the range of -90° to 90° by traversing β1 and β2.

[0053] Taking device A as an example, a planar array can be constructed using devices A with different β1 and β2 as basic units, enabling dynamic switching between arbitrary linearly polarized optical fields. (See also...) Figure 3 B. Adjust β1 and β2 of each unit so that it outputs radially polarized linearly polarized light in the insulating state and tangentially polarized linearly polarized light in the metallic state, thereby achieving dynamic switching between radially polarized vortices and tangentially polarized vortices. If β1 and β2 of each unit are adjusted so that the polarization directions of the linearly polarized light output in the insulating and metallic states are l1θ and l2θ respectively (l1, l2 = ±1, ±2, ..., l1 ≠ l2 is the topological charge, and θ is the polar angle of the unit's position in the polar coordinate system), then dynamic switching between vortex beams with different topological charges can be achieved.

[0054] Example 4

[0055] This invention proposes a principle for achieving dynamic switching between arbitrary polarization states based on a tunable vanadium dioxide dynamically switching terahertz waveplate.

[0056] The waveplate phase difference of the device in the two states can be adjusted by the structural parameters of the array cells without changing the substrate thickness and array period. Please refer to... Figure 4 Based on device A, the phase difference in the insulating state can be adjusted within a certain range by the angle α of the C-SRR, and the phase difference in the metallic state can be adjusted within a certain range by the antenna length L. Furthermore, by selecting different combinations of the outer and inner radii of the C-SRR (Combination 1: R = 75 μm, r = 45 μm; Combination 2: R = 60 μm, r = 40 μm; Combination 3: R = 75 μm, r = 35 μm), the adjustment range of the phase difference in the insulating and metallic states can be extended to 0°–180°. Please refer to [link to relevant documentation]. Figure 4 When B,x-polarized light is incident on the surface of a waveplate, if the fast / slow axis direction of the waveplate can be arbitrarily selected within the range of -90° to 90°, and the phase difference can be arbitrarily selected within the range of 0° to 180°, then any polarization state can be obtained. The dynamic switching terahertz waveplate described in this invention allows for independent adjustment of the fast / slow axis direction and phase difference in both insulating and metallic states. Furthermore, the fast / slow axis direction can be arbitrarily selected within the range of -90° to 90°, and the phase difference can be arbitrarily selected within the range of 0° to 180°, thus enabling dynamic switching between arbitrary polarization states. Figure 4 C shows the polarization states that can be obtained under combination 2. The left side shows the Poincaré sphere in the insulating state, and the right side shows the Poincaré sphere in the metallic state. The yellow area represents the polarization states that can be obtained. The yellow area covers almost the entire surface of the Poincaré sphere.

[0057] The Poincaré sphere is a unit sphere on which each point corresponds to a specific polarization state. This sphere is built on a Cartesian coordinate system (S1, S2, S3), where S1, S2, and S3 are Stokes parameters, directly corresponding to the parameters of the polarization ellipse. The equator of the Poincaré sphere represents the collection of linearly polarized light; the polarization direction at each point on the equator rotates with increasing longitude. The south and north poles of the Poincaré sphere represent left-handed and right-handed circularly polarized light, respectively. The other points on the surface of the Poincaré sphere represent elliptically polarized light, and their positions are determined by the orientation angle (angle with the X-axis) and ellipticity (ratio of the minor axis to the major axis) of the polarization ellipse.

[0058] Currently, non-mechanically controlled dynamically switching terahertz waveplates have coupled fast / slow axis directions in different operating modes (in most cases, they share the same fast / slow axis direction). When the fast / slow axis direction in one operating mode is adjusted, the fast / slow axis directions in other operating modes also change accordingly, which greatly limits the functions that the device can achieve. For example, dynamic switching between arbitrary linearly polarized light fields requires all units to exhibit the properties of a quarter-wave plate (circularly polarized light incident, phase difference of 90°) or a half-wave plate (linearly polarized light incident, phase difference of 180°) in different operating modes, and the fast / slow axes in different operating modes can be independently controlled. Otherwise, the polarization direction of the output linearly polarized light in different operating modes is interrelated, making it impossible to achieve "arbitrary". The mode-decoupled dynamically switching terahertz waveplate proposed in this invention cleverly utilizes the phase transition characteristics of vanadium dioxide to construct an optical axis-decoupled metal-vanadium dioxide composite metasurface, solving this problem. Moreover, the phase difference of the device in the two operating modes can also be independently controlled, based on which dynamic switching between arbitrary polarization states can be achieved.

[0059] In summary, this invention proposes a mode-decoupled dynamically switching terahertz waveplate. The waveplate, from top to bottom, comprises a metal-vanadium dioxide composite metasurface, a quartz substrate, and a metal reflective layer. The metal-vanadium dioxide composite metasurface includes patterned metal and patterned vanadium dioxide. The patterned vanadium dioxide exhibits phase transition characteristics, enabling the waveplate to dynamically switch between two independent waveplate modes. These two independent waveplate modes are decoupled modes. The waveplate exhibits waveplate properties in both insulating and metallic states, and the fast / slow axis directions and phase difference of the waveplate in both states can be independently controlled. This invention also proposes an optical axis-decoupled metal-vanadium dioxide composite metasurface. By utilizing the phase transition characteristics of vanadium dioxide, the resonant characteristics of the metasurface are modulated, causing it to exhibit optical axis decoupling characteristics, thereby constructing a mode-decoupled dynamically switching terahertz waveplate. Based on this mode-decoupling characteristic, the device can achieve dynamic switching between arbitrary linearly polarized light fields and between arbitrary polarization states. This invention provides a more flexible and convenient approach to dynamic terahertz polarization modulation.

[0060] It should be noted that the term "comprising," or any other variation thereof, is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0061] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A mode-decoupled dynamically switching terahertz waveplate, characterized in that, The waveplate consists of, from top to bottom, a metal-vanadium dioxide composite metasurface, a quartz substrate, and a metal reflective layer; The metal-vanadium dioxide composite metasurface comprises patterned metal and patterned vanadium dioxide; The patterned vanadium dioxide has phase transition properties, enabling the waveplate to dynamically switch between two independent waveplate modes. The two independent waveplate modes are decoupled modes; The two independent waveplate modes are modes in which the fast / slow axes and phase difference can be independently adjusted; The waveplate is used to achieve dynamic switching between arbitrary linearly polarized light fields; The waveplate is used to achieve dynamic switching between arbitrary polarization states; The quartz substrate is used to achieve precise control and transmission of terahertz waves; The metal reflective layer is used to shield the transmission channel and eliminate transmission energy loss.

2. The dynamically switched terahertz waveplate with mode decoupling according to claim 1, characterized in that, The metal-vanadium dioxide composite metasurface includes array units; The array unit comprises metallic C-SRR and patterned vanadium dioxide; The patterned vanadium dioxide fills the gap in the metal C-SRR and extends into a rectangular antenna.

3. The dynamically switched terahertz waveplate with mode decoupling according to claim 1, characterized in that, The phase transition characteristics of the patterned vanadium dioxide are the characteristics of the patterned vanadium dioxide transitioning between an insulating phase and a metallic phase. The waveplate's fast / slow axis under the insulating phase is along the angle bisector of the notch in the metal C-SRR; The waveplate's fast / slow axis is along the long side of the antenna in the metallic phase; The waveplate can take any value in the fast / slow axis direction within the range of -90° to 90° under the insulating phase and the metallic phase.

4. The mode-decoupled dynamically switched terahertz waveplate according to claim 3, characterized in that, The phase difference between the waveplate under the insulating phase and the waveplate under the metallic phase can be adjusted by the structural parameters of the array unit without changing the substrate thickness and array period. The waveplate phase difference under the insulating phase can be adjusted by the angle of the metal C-SRR; The waveplate phase difference under the metallic phase can be adjusted by the length of the antenna.

5. The mode-decoupled dynamically switched terahertz waveplate according to claim 3, characterized in that, The mode decoupling characteristics of the waveplate are based on the generation or disappearance of electric dipole resonance and magnetic dipole resonance in the metal-vanadium dioxide composite metasurface induced by the phase transition of the patterned vanadium dioxide.

6. The mode-decoupled dynamically switched terahertz waveplate according to any one of claims 1 to 5, characterized in that, The waveplate can achieve dynamic switching from one quarter-wave plate to another, from one quarter-wave plate to another, from one half-wave plate to another, or from one half-wave plate to another.

7. The mode-decoupled dynamically switched terahertz waveplate according to claim 6, characterized in that, The waveplate includes device A, device B, device C, or device D; The device A is capable of dynamic switching from one quarter-wave plate to the other. The device B is capable of dynamically switching from a quarter-wave plate to a half-wave plate; The device C can achieve dynamic switching from half-wave plate to half-wave plate; The device D can achieve dynamic switching from a half-wave plate to a quarter-wave plate; Devices A, B, C, and D all possess the mode decoupling characteristic.

8. The mode-decoupled dynamically switched terahertz waveplate according to claim 7, characterized in that, The planar array constructed from the device A or the device C with different fast / slow axis directions as basic units can be used for dynamic switching between arbitrary linearly polarized light fields. The dynamic switching between arbitrary linearly polarized light fields includes dynamic switching between radially and tangentially polarized vortex beams, or dynamic switching between polarized vortex beams with different topological charges.

9. The mode-decoupled dynamically switched terahertz waveplate according to claim 8, characterized in that, The waveplate phase difference between the insulating phase and the metallic phase can be independently adjusted by changing the opening angle and radius of the metallic C-SRR, and / or the length of the antenna. By adjusting the phase difference of the waveplate and / or the direction of the fast / slow axis, the waveplate can achieve dynamic switching between arbitrary polarization states.

10. The mode-decoupled dynamically switched terahertz waveplate according to claim 1, characterized in that, The waveplate has a MIM-like structure.

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