Switchable broadband terahertz multifunctional wave plate

Abstract

The switchable broadband terahertz multifunctional wave plate comprises a vanadium dioxide thin film layer, a first dielectric layer, a first micro-nano structure layer, a second dielectric layer and a second micro-nano structure layer which are stacked in sequence, adjusting the phase change temperature of the vanadium dioxide thin film layer to enable the vanadium dioxide thin film layer to change between an insulating phase and a metal phase; when the vanadium dioxide thin film layer is an insulating phase, the switchable broadband terahertz multifunctional wave plate is a quarter-wave plate; when the vanadium dioxide thin film layer is in a metal phase, the switchable broadband terahertz multifunctional wave plate is a half-wave plate; the function of the quarter-wave plate and the function of the half-wave plate are integrated, switching is achieved by adjusting the phase-change temperature, the conversion requirement of polarized light can be met, and reversible conversion is achieved.

Description

Technical Field

[0001] The invention relates to the field of terahertz band metasurface functional devices, and in particular to a switchable wide-band terahertz multifunctional wave plate. Background Art

[0002] Terahertz waves usually refer to electromagnetic waves with a frequency in the range of 0.1THz-10 THz and a wavelength in the range of 30μm-3000μm, which is between microwaves and infrared light in the electromagnetic spectrum. Due to its excellent penetration ability, sensitivity to matter and non-destructive detection characteristics, terahertz waves have shown broad application prospects in the fields of communications, imaging, medical treatment, biological detection and security. However, the regulation and control of terahertz waves still face huge challenges, especially in polarization state control and wavefront adjustment. Although traditional optical components, such as lenses, reflectors and wave plates, have achieved remarkable results in the visible light and infrared spectra, in the terahertz band, due to the long wavelength and complex interaction with materials, existing devices are difficult to meet the needs of efficient and precise regulation.

[0003] Wave plates are optical components that can adjust the polarization state of light waves. Common ones include quarter-wave plates and half-wave plates. Quarter-wave plates can convert circularly polarized light into linearly polarized light, while half-wave plates can rotate linearly polarized light 180 degrees. The design of traditional wave plates usually relies on the birefringence effect of the material. By adjusting the thickness, refractive index and other parameters of the material, the propagation speed of electromagnetic waves in different polarization directions is changed, thereby achieving polarization state control. However, the application of these traditional materials in the terahertz band is limited, mainly reflected in the component size, processing accuracy and wavelength matching, which makes it impossible to efficiently and accurately control the polarization state and wavefront of terahertz waves.

[0004] In recent years, metasurface technology, as an emerging electromagnetic wave control technology, has provided a possible solution. Metasurfaces can accurately control the phase, amplitude and polarization state of electromagnetic waves through artificially designed microscopic structural units. Compared with traditional materials, metasurface wave plates have stronger control capabilities and higher flexibility. Through periodically arranged micro-nano structures, metasurfaces can achieve phase adjustment in the terahertz band, thereby accurately controlling the conversion and rotation of polarized light. This new wave plate design not only overcomes the size and processing limitations of traditional materials, but also provides a new direction for the integration and multifunctionality of terahertz optical systems.

[0005] Therefore, it is necessary to solve the problem that traditional terahertz wave plates can only realize a single function and it is difficult to simultaneously meet the different conversion requirements of polarized light, and traditional terahertz wave plates are irreversible. Summary of the invention

[0006] The purpose of the present invention is to provide a switchable broadband terahertz multifunctional wave plate to solve the problem that the terahertz wave plate in the prior art can only realize a single function, is difficult to simultaneously meet the different conversion requirements of polarized light, and is irreversible.

[0007] To achieve the above object, the present invention provides the following technical solutions: A switchable broadband terahertz multifunctional wave plate comprises a vanadium dioxide film layer, a first dielectric layer, a first micro-nano structure layer, a second dielectric layer and a second micro-nano structure layer which are stacked in sequence; the phase change temperature of the vanadium dioxide film layer is adjusted so that the vanadium dioxide film layer changes between an insulating phase and a metallic phase; when the vanadium dioxide film layer is in an insulating phase, the switchable broadband terahertz multifunctional wave plate is a quarter wave plate; when the vanadium dioxide film layer is in a metallic phase, the switchable broadband terahertz multifunctional wave plate is a half wave plate.

[0008] Preferably, the conductivity of the vanadium dioxide film layer is w p , when the vanadium dioxide film layer is an insulating phase, w p The value of is 10 S / m. When the vanadium dioxide film layer is in the metal phase, w p The value is 2´10 5 S / m.

[0009] Preferably, when the vanadium dioxide thin film layer is in an insulating phase, the incident light is 45-degree linear polarized light or circular polarized light; when the vanadium dioxide thin film layer is in a metallic phase, the incident light is 45-degree linear polarized light; the incident light is perpendicular to the switchable wide-band terahertz multifunctional wave plate.

[0010] Preferably, the first micro-nanostructure layer and the second micro-nanostructure layer are both provided with a rectangular structure and a periodic structure symmetrically arranged on both sides of the rectangular structure, the periodic structure includes 5 T-shaped structures extending along the length direction of the rectangular structure, and the narrow side of the T-shaped structure extends toward one side of the rectangular structure.

[0011] Preferably, the length of the long side of the rectangular structure is a 1, a 1 is 83.4 μm, and the short side length of the rectangular structure is a 2, a 2 is 2 μm; the length of the long side of the transverse portion of the T-shaped structure is b 1, b 1 is 13.4 μm, and the short side length of the transverse portion of the T-shaped structure is c 2, c 2 is 6.7 μm; the short side length of the vertical portion of the T-shaped structure is b 2,b 2 is 6.7 μm, and the length of the long side of the vertical portion of the T-shaped structure is c 1, c 1 is 30 μm.

[0012] Preferably, the distance between the vertical parts of two adjacent T-shaped structures is b 3. b 3 is 10 μm.

[0013] Preferably, the period length of the first micro-nano structure layer and the second micro-nano structure layer along the first direction is P x , the period length along the second direction is P y , the first direction is perpendicular to the second direction, P x = P y =83.4 μm; the thickness of the first micro-nano structure layer and the second micro-nano structure layer is h 3. h 3 is 0.2 μm.

[0014] Preferably, the thickness of the vanadium dioxide film layer is h 1, h 1 is 1 μm; the thickness of the first dielectric layer is h 2, h 2 is 6.7 μm; the thickness of the second dielectric layer is h 4. h 4 is 27.3 μm.

[0015] Preferably, the first micro-nano structure layer and the second micro-nano structure layer are both made of gold, and the first dielectric layer and the second dielectric layer are both made of cycloolefin copolymer.

[0016] Preferably, the operating frequency range of the switchable broadband terahertz multifunctional wave plate is 0.80 THz to 1.68 THz.

[0017] Beneficial effects: The overall structure of the multifunctional wave plate is formed by stacking a vanadium dioxide thin film layer, a first dielectric layer, a first micro-nano structure layer, a second dielectric layer and a second micro-nano structure layer in sequence, wherein the first micro-nano structure layer and the second micro-nano structure layer can finely control the polarization characteristics and phase characteristics of the terahertz wave, realize the polarization conversion and polarization direction rotation of the terahertz wave, improve the sensitivity and resolution, and can be adapted to the application in gas, liquid and biosensors; At the same time, the phase change characteristics of vanadium dioxide are utilized to change its phase change temperature to realize the switching of the entire multifunctional wave plate to a quarter wave plate function or a half wave plate function, and the two functions are integrated into one to realize function switching; when converted to the quarter wave plate function, it can realize 45-degree linear polarized light incident and circular polarized light emission, or circular polarized light incident and 45-degree linear polarized light emission, with reversible conversion; and when converted to the half wave plate function, it has a high linear polarization degree, and realizes -45-degree linear polarized light emission when 45-degree linear polarized light is incident; At the same time, the entire structure is simpler, convenient for batch preparation, and has stable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of a switchable broadband terahertz multifunctional wave plate device of the present invention; Figure 2 A schematic diagram of the structure of the first micro-nano structure layer and the second micro-nano structure layer in the present invention; Figure 3 for Figure 2 A side view schematic diagram of the structure; Figure 4 This is a graph of the ellipticity of the outgoing circularly polarized light when the linearly polarized light is incident at 45 degrees under the function of a quarter wave plate of the present invention; Figure 5 The polarization conversion efficiency curve of the outgoing circularly polarized light when the linearly polarized light of 45 degrees is incident under the function of the quarter wave plate of the present invention; Figure 6 It is the intensity pole figure of the outgoing circular polarized light when the linear polarized light of 45 degrees is incident under the function of the quarter wave plate of the present invention; Figure 7 The linear polarization degree curve diagram of the 45 degree linear polarization light emitted when the circular polarization light is incident under the function of the quarter wave plate of the present invention; Figure 8 It is the light intensity pole figure of the 45 degree linear polarized light emitted when circular polarized light is incident under the function of a quarter wave plate of the present invention; Fig. 9 The polarization conversion rate curve of the outgoing -45 degree linear polarized light when the 45 degree linear polarized light is incident under the function of the half-wave plate of the present invention; Fig.10 It is a graph of the extinction ratio of the outgoing -45 degree linear polarized light when the 45 degree linear polarized light is incident under the function of the half-wave plate of the present invention; Fig.11 It is the intensity pole figure of the outgoing -45 degree linear polarized light when 45 degree linear polarized light is incident under the function of the half-wave plate of the present invention; exist Figures 1 to 11 In the figure, the corresponding relationship between the component names or lines and the figure numbers is as follows: Vanadium dioxide thin film layer 1, first dielectric layer 2, first micro-nano structure layer 3, second dielectric layer 4, second micro-nano structure layer 5. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0020] See also Figure 1 As shown, in an embodiment of the present invention, a switchable wide-band terahertz multifunctional wave plate is proposed, comprising a vanadium dioxide thin film layer 1, a first dielectric layer 2, a first micro-nano structure layer 3, a second dielectric layer 4 and a second micro-nano structure layer 5 stacked in sequence, and the stacking direction is along the z direction, wherein the first micro-nano structure layer 3 and the second micro-nano structure layer 5 can adjust the phase, polarization, amplitude and other characteristics of the terahertz wave, and realize polarization conversion and polarization direction rotation; the entire structure is simplified and easy to prepare, and can be widely used in the fields of gas, liquid, biosensors, etc., and can be involved in medical imaging, environmental monitoring and other scenarios. The integrated structure realizes the switching between the quarter-wave plate function and the half-wave plate function. The function switching is mainly realized by the phase change of the vanadium dioxide film layer 1. Specifically, the phase change temperature of the vanadium dioxide film layer 1 is adjusted so that the vanadium dioxide film layer 1 changes between the insulating phase and the metallic phase. When the vanadium dioxide film layer 1 is in the insulating phase, the switchable broadband terahertz multifunctional wave plate is a quarter-wave plate. When the vanadium dioxide film layer 1 is in the metallic phase, the switchable broadband terahertz multifunctional wave plate is a half-wave plate. Since the conductivity of vanadium dioxide (VO2) has significant temperature dependence and has significant temperature-driven phase change characteristics, its phase change temperature is about 68°C, realizing the mutual conversion between the metallic phase and the insulating phase, thereby realizing the function switching of the entire multifunctional wave plate. When the phase transition temperature is lower than 68°C, it transforms into an insulating phase, and when it is higher than 68°C, it transforms into a metallic phase. Thus, it has reversible transformation properties. According to actual functional requirements, the ambient temperature is adjusted to realize the switching of the vanadium dioxide thin film layer 1 between the insulating phase and the metallic phase, thereby realizing the switching of the entire multifunctional wave plate between the quarter-wave plate function and the half-wave plate function, thereby improving the scope of application.

[0021] In order to satisfy the conductivity requirements and insulation requirements of the vanadium dioxide film layer 1 after the conversion between the metal phase and the insulating phase, the conductivity of the vanadium dioxide film layer 1 is w p , when the vanadium dioxide film layer 1 is an insulating phase, w p The value of is 10 S / m. When the vanadium dioxide film layer 1 is in the metal phase, w p The value is 2´10 5 S / m.

[0022] Specifically, when realizing the function of a quarter wave plate, the light absorption and reflection are relatively weak, while when realizing the function of a half wave plate, the light absorption and reflection are relatively high. Therefore, when the vanadium dioxide thin film layer 1 is in an insulating phase, the function of a quarter wave plate is realized, and the incident light is 45-degree linear polarized light or circularly polarized light; when the vanadium dioxide thin film layer 1 is in a metallic phase, the function of a half wave plate is realized, and the incident light is 45-degree linear polarized light; the incident light is perpendicular to the switchable wide-band terahertz multifunctional wave plate.

[0023] The first micro-nanostructure layer 3 and the second micro-nanostructure layer 5 realize precise control of the phase, amplitude and polarization characteristics of the terahertz wave and enhance the broadband characteristics. Specifically, the first micro-nanostructure layer 3 and the second micro-nanostructure layer 5 are both provided with a rectangular structure and a periodic structure symmetrically arranged on both sides of the rectangular structure, wherein the periodic structure includes five T-shaped structures extending along the length direction of the rectangular structure, and the narrow side of the T-shaped structure extends toward one side of the rectangular structure.

[0024] At the same time, in order to obtain more accurate detection results, the parameters of the first micro-nano structure layer 3 and the second micro-nano structure layer 5 are optimized, wherein, Figure 2 As shown, the length of the long side of the rectangular structure is a 1, a 1 is 83.4 μm, and the short side length of the rectangular structure is a 2, a 2 is 2 μm; the length of the long side of the transverse portion of the T-shaped structure is b 1, b 1 is 13.4 μm, and the short side length of the transverse portion of the T-shaped structure is c 2, c 2 is 6.7 μm; the short side length of the vertical portion of the T-shaped structure is b 2, b 2 is 6.7 μm, and the length of the long side of the vertical portion of the T-shaped structure is c 1, c 1 is 30 μm.

[0025] In the same periodic structure, the distance between the vertical parts of the two T-shaped structures is b 3. b 3 is 10 μm.

[0026] This can improve the detection accuracy of actual products.

[0027] At the same time, the size of the entire multifunctional wave plate is also optimized to control the integration degree, so that the period length of the first micro-nano structure layer 3 and the second micro-nano structure layer 5 along the first direction is Px , the period length along the second direction is P y , the first direction is perpendicular to the second direction, P x = P y =83.4 μm; the thickness of the first micro-nanostructure layer 3 and the second micro-nanostructure layer 5 is h 3. h 3 is 0.2 μm.

[0028] The stacking height also has a certain influence on the results of the entire multifunctional wave plate in achieving high-precision detection. At the same time, parameter optimization is performed, such as Figure 3 As shown, the thickness of the vanadium dioxide film layer 1 is h 1, h 1 is 1 μm; the thickness of the first dielectric layer 2 is h 2, h 2 is 6.7 μm; the thickness of the second dielectric layer 4 is h 4. h 4 is 27.3 μm.

[0029] In order to meet the working frequency requirements of the first micro-nano structure layer 3 and the second micro-nano structure layer 5, the materials of the first micro-nano structure layer 3 and the second micro-nano structure layer 5 are both gold. The first dielectric layer 2 and the second dielectric layer 4 mainly play the role of separation and support, and avoid affecting the performance of the first micro-nano structure layer 3 and the second micro-nano structure layer 5. Therefore, the materials of the first dielectric layer 2 and the second dielectric layer 4 are both cycloolefin copolymers.

[0030] The operating frequency range of the stacked switchable wide-band terahertz multifunctional wave plate is 0.80 THz~1.68 THz.

[0031] Based on the stacked shell switch wide-band terahertz multifunctional wave plate in this embodiment, the function of a quarter wave plate and a half wave plate can be switched. In order to verify the specific functions implemented, when switching to the quarter wave plate function, the incident light can be 45-degree linear polarized light or circular polarized light, and the conversion from 45-degree linear polarized light to circular polarized light, or from circular polarized light to 45-degree linear polarized light can be realized.

[0032] The conversion process from linearly polarized light to circularly polarized light can be described by the Stokes parameter representation: , in, T xx and T yy express x Direction andy The transmission amplitude of the directional polarization, S0 represents the total intensity of light, including polarization components, S1 represents the linear polarization component of light, representing the polarization intensity difference between the horizontal and vertical directions, S2 represents the polarization intensity difference between the 45° and 135° directions, and S3 represents the circular polarization component of light, representing the intensity difference between right-handed and left-handed circular polarization of light. Figure 4 As shown in the figure, when 45 degrees linear polarized light is incident under the function of a quarter wave plate, the ellipticity curve of the outgoing circularly polarized light is defined as , at this time, in the 0.80 THz to 1.26 THz band, the ellipticity is greater than 0.99, and the emitted circularly polarized light is good, with the best effect at 1.18 THz; see Figure 5 As shown in the figure, when 45 degree linear polarized light is incident under the function of a quarter wave plate, the polarization conversion efficiency curve of the outgoing circular polarized light is defined as , in the 0.80 THz to 1.26 THz band, the average efficiency is calculated to be 76.37%; see Figure 6 As shown, when 45-degree linear polarized light is incident under the function of a quarter-wave plate, the intensity pole figure of the outgoing circularly polarized light is obtained, and the intensity pole figure of the circularly polarized light at 1.18 THz is obtained, which is very close to the intensity pole figure of a perfect circularly polarized light.

[0033] The conversion process from circularly polarized light to linearly polarized light can also be described by the Stokes parameter representation: , in, T xy and T yy express y Polarization x Direction and y Direction: Transmission amplitude in the polarization direction, S0 represents the total intensity of light, including polarization components, S1 represents the linear polarization component of light, representing the polarization intensity difference between the horizontal and vertical directions, S2 represents the polarization intensity difference between the 45° and 135° directions, and S3 represents the circular polarization component of light, representing the intensity difference between right-handed and left-handed circular polarization of light. Figure 7 As shown in the figure, when circularly polarized light is incident under the function of a quarter wave plate, the linear polarization degree curve of the emitted 45 degree linear polarized light is defined as , in the 0.80THz to 1.28 THz band, the linear polarization degree is greater than 0.99, emitting good linear polarized light, with the best effect at 1.21 THz; see Figure 8As shown, when circularly polarized light is incident under the function of a quarter wave plate, the intensity pole figure of the emitted 45-degree linearly polarized light is obtained, and the intensity pole figure of the linearly polarized light at 1.21 THz is obtained, which is very close to the intensity pole figure of a perfect 45-degree linearly polarized light.

[0034] Therefore, when realizing the function of a quarter wave plate, it can realize that 45-degree linear polarized light is incident and circular polarized light is emitted; it can also realize that circular polarized light is incident and 45-degree linear polarized light is emitted. The reversible conversion of polarization state is realized, which plays an important role in polarization optics and optical communications.

[0035] When the half-wave plate is used, the incident light is 45-degree linear polarized light, and the outgoing light is -45-degree linear polarized light, which has a good polarization conversion rate. Fig. 9 As shown in the figure, under the function of half-wave plate, when 45 degree linear polarized light is incident, the polarization conversion efficiency curve of -45 degree linear polarized light is emitted. The polarization conversion rate is defined as ,in, , . R xx and R yy express x Direction and y The reflection amplitude of directional polarization is greater than 0.9 in the 0.97 THz to 1.68 THz band, and good linear polarization light is emitted, with the best effect at 1.54 THz; see Fig.10 As shown in the figure, under the half-wave plate function, when 45-degree linear polarized light is incident, the extinction ratio curve of the outgoing -45-degree linear polarized light is defined as , greater than 15 dB in the entire band from 0.50 THz to 1.90 THz, with a relatively ideal polarization state; see Fig.11 As shown, when 45-degree linear polarized light is incident under the function of the half-wave plate, the intensity pole figure of the outgoing -45-degree linear polarized light is obtained, and the intensity pole figure of the linear polarized light at 1.54 THz is obtained, which is very close to the intensity pole figure of a perfect linear polarized light.

[0036] Therefore, we can believe that the switchable broadband terahertz multifunctional wave plate device in this embodiment can realize the function of a quarter wave plate, and the conversion from linear polarized light to circular polarized light can reach 0.46 THz; it can realize the conversion from linear polarized light to circular polarized light, and its bandwidth can reach 0.48 THz, realizing the reversible conversion of polarization state. At the same time, it can switch to realize the function of a half wave plate, and the conversion from linear polarized light to linear polarized light can reach 0.71 THz.

[0037] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "inner", "outer", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0039] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A switchable broadband terahertz multifunctional wave plate, characterized in that: It comprises a vanadium dioxide thin film layer (1), a first dielectric layer (2), a first micro-nano structure layer (3), a second dielectric layer (4) and a second micro-nano structure layer (5) which are stacked in sequence; The phase transition temperature of the vanadium dioxide film layer (1) is adjusted so that the vanadium dioxide film layer (1) changes between an insulating phase and a metallic phase; when the vanadium dioxide film layer (1) is in the insulating phase, the switchable broadband terahertz multifunctional wave plate is a quarter-wave plate; when the vanadium dioxide film layer (1) is in the metallic phase, the switchable broadband terahertz multifunctional wave plate is a half-wave plate.

2. The switchable broadband terahertz multifunctional wave plate according to claim 1, characterized in that: The conductivity of the vanadium dioxide film layer (1) is w p , when the vanadium dioxide film layer (1) is an insulating phase, w p The value of is 10 S / m. When the vanadium dioxide film layer (1) is a metal phase, w p The value is 2´10 5 S / m.

3. The switchable broadband terahertz multifunctional wave plate according to claim 2, characterized in that: When the vanadium dioxide film layer (1) is in an insulating phase, the incident light is 45-degree linear polarized light or circular polarized light; when the vanadium dioxide film layer (1) is in a metallic phase, the incident light is 45-degree linear polarized light; The incident light is perpendicular to the switchable broadband terahertz multifunctional wave plate.

4. A switchable broadband terahertz multifunctional wave plate according to any one of claims 1 to 3, characterized in that: The first micro-nanostructure layer (3) and the second micro-nanostructure layer (5) are both provided with a rectangular structure and a periodic structure symmetrically arranged on both sides of the rectangular structure, wherein the periodic structure comprises five T-shaped structures extending along the length direction of the rectangular structure, and the narrow sides of the T-shaped structures extend towards one side of the rectangular structure.

5. The switchable broadband terahertz multifunctional wave plate according to claim 4, characterized in that: The length of the long side of the rectangular structure is a 1, a 1 is 83.4 μm, and the short side length of the rectangular structure is a 2, a 2 is 2 μm; The length of the long side of the transverse portion of the T-shaped structure is b 1, b 1 is 13.4 μm, and the short side length of the transverse portion of the T-shaped structure is c 2, c 2 is 6.7 μm; The short side length of the vertical portion of the T-shaped structure is b 2, b 2 is 6.7 μm, and the length of the long side of the vertical portion of the T-shaped structure is c 1, c 1 is 30 μm.

6. The switchable broadband terahertz multifunctional wave plate according to claim 5, characterized in that: The distance between the vertical parts of two adjacent T-shaped structures is b 3. b 3 is 10 μm.

7. The switchable broadband terahertz multifunctional wave plate according to claim 6, characterized in that: The period length of the first micro-nanostructure layer (3) and the second micro-nanostructure layer (5) along the first direction is P x , the period length along the second direction is P y , the first direction is perpendicular to the second direction, P x = P y =83.4 μm; The thickness of the first micro-nanostructure layer (3) and the second micro-nanostructure layer (5) is h 3. h 3 is 0.2 μm.

8. The switchable broadband terahertz multifunctional wave plate according to claim 7, characterized in that: The thickness of the vanadium dioxide film layer (1) is h 1, h 1 is 1 μm; the thickness of the first dielectric layer (2) is h 2, h 2 is 6.7 μm; the thickness of the second dielectric layer (4) is h 4. h 4 is 27.3 μm.

9. The switchable broadband terahertz multifunctional wave plate according to claim 8, characterized in that: The materials of the first micro-nano structure layer (3) and the second micro-nano structure layer (5) are both gold, and the materials of the first dielectric layer (2) and the second dielectric layer (4) are both cycloolefin copolymer.

10. The switchable broadband terahertz multifunctional wave plate according to claim 9, characterized in that: The switchable broadband terahertz multifunctional wave plate operates in the frequency range of 0.80 THz to 1.68 THz.

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