A terahertz super surface device capable of realizing multi-polarization regulation

Abstract

The application discloses a terahertz super surface device capable of realizing multi-polarization regulation, which comprises a first dielectric layer, a second dielectric layer and a third dielectric layer which are stacked in sequence, a first micro-nano structure layer is stacked on the first dielectric layer, a second micro-nano structure layer is stacked on the second dielectric layer, and a third micro-nano structure layer is stacked on the third dielectric layer; the first micro-nano structure layer is the same as the third micro-nano structure layer and both are Z-shaped structures; the second micro-nano structure layer comprises a negative structure metal layer stacked on the second dielectric layer and a vanadium dioxide layer located in the middle of the negative structure metal layer, and the vanadium dioxide layer is in a cross-shaped structure; a dielectric protective layer is covered on the first micro-nano structure layer; the reflection quarter-wave plate and full-space half-wave plate functions are realized, the conversion from linearly polarized light to left-handed circularly polarized light, right-handed circularly polarized light and orthogonal linearly polarized light can be realized in different frequency bands, and the limitation of single function of a traditional device is solved.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave modulation technology, and in particular to a terahertz metasurface device capable of multi-polarization modulation. Background Technology

[0002] Polarization, a fundamental characteristic of electromagnetic waves, plays a crucial role in the interaction between light and matter. In the terahertz band, precise polarization control shows broad application prospects in fields such as communication, optical imaging, biological detection, and remote sensing. However, precise manipulation of terahertz waves still faces significant challenges, especially in multi-polarization state control and wavefront modulation. Furthermore, traditional terahertz polarization control elements still face challenges in miniaturization, integration, and high performance.

[0003] To achieve precise polarization control, metasurface technology, as an emerging electromagnetic wave manipulation technique, offers a possible solution. Metasurfaces, through artificially designed microscopic structural units, can precisely control the phase, amplitude, and polarization of electromagnetic waves. Compared to traditional materials, metasurfaces are much thinner than the operating wavelength, significantly reducing the thickness of electromagnetic devices and facilitating miniaturization, planarization, and diversified design. Precise polarization control can be achieved through periodically arranged structural units; furthermore, high-quality wavefront manipulation can be achieved through specific arrangements of structural units. In particular, metasurfaces can be used to design multifunctional waveplate devices that function as multi-band reflection quarter-wave plates and full-space half-wave plates, enabling precise manipulation of multiple polarizations. Based on this, arbitrary polarization holographic imaging can be obtained using the GS algorithm, overcoming the requirements for incident light. This waveplate metasurface design not only overcomes the size and processing limitations of traditional materials but also opens up new avenues for the integration and multifunctionality of terahertz optical systems. Existing multi-polarization controlled terahertz waveplate devices are based on frequency reuse, making it difficult to achieve designable multi-band multi-polarization control. Summary of the Invention

[0004] (a) Technical issues

[0005] The purpose of this invention is to provide a terahertz metasurface device that can achieve multi-polarization control, solving the problem that most existing multi-polarization control terahertz waveplates rely on frequency and can only achieve a single polarization conversion function.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A terahertz metasurface device capable of multi-polarization control includes a first dielectric layer, a second dielectric layer, and a third dielectric layer stacked sequentially. A first micro / nano structure layer is stacked on the first dielectric layer, a second micro / nano structure layer is stacked on the second dielectric layer, and a third micro / nano structure layer is stacked on the third dielectric layer. The first and third micro / nano structure layers are identical, both exhibiting a Z-shaped structure. The second micro / nano structure layer includes a negative structure metal layer stacked on the second dielectric layer and a vanadium dioxide layer located in the middle of the negative structure metal layer, the vanadium dioxide layer exhibiting a cross-shaped structure. A dielectric protective layer covers the first micro / nano structure layer.

[0009] Preferably, the first and third micro / nano structure layers are made of gold, with an electrical conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0010] Preferably, the first dielectric layer, the second dielectric layer, the third dielectric layer, and the dielectric protective layer are all made of cyclic olefin copolymers with a relative permittivity of 2.1 + 0.006i, where i is the imaginary unit, satisfying i 2 =﹣1.

[0011] Preferably, the first micro / nano structure layer and the third micro / nano structure layer have a rotation angle γ relative to the second dielectric layer or the third dielectric layer, where γ is 55°.

[0012] Preferably, the period lengths of the first micro / nano structure layer, the second micro / nano structure layer, and the third micro / nano structure layer along the x and y directions are P, where P is 50 μm.

[0013] Preferably, the parameters of the first micro / nano structure layer and the third micro / nano structure layer include:

[0014] Overall height is , It is 32 μm;

[0015] The length of the outer straight arm is , It is 32 μm;

[0016] The length of the inner straight arm is , It is 26 μm;

[0017] The height of the slant arm is , It is 24 μm;

[0018] The thickness is t1, which is 0.2 μm.

[0019] Preferably, the parameters of the second micro / nano structure layer include:

[0020] The length of the longer side is c1, and c1 is 42 μm;

[0021] The shorter side has a length of c2, and c2 is 10 μm.

[0022] The thickness is t2, which is 0.5 μm.

[0023] Preferably, the thickness of the first dielectric layer is l2, and l2 is 8 μm;

[0024] The thickness of the second dielectric layer is l3, and l3 is 9 μm;

[0025] The thickness of the third dielectric layer is l4, and l4 is 3 μm;

[0026] The thickness of the dielectric protective layer is l1, and l1 is 3 μm.

[0027] Preferably, the electrical conductivity of the vanadium dioxide layer is w p Based on changes in the external ambient temperature, when w p When the value of is 10 S / m, the vanadium dioxide layer is in transmission mode; when w p The value is 2×10 5 At S / m, the vanadium dioxide layer is in reflection mode.

[0028] Preferably, when the vanadium dioxide layer is in reflection mode, the terahertz metasurface device operates in a simultaneous quarter-wave plate and half-wave plate mode; when the vanadium dioxide layer is in transmission mode, the terahertz metasurface device operates in a half-wave plate mode.

[0029] (III) Beneficial Effects

[0030] Through the collaborative design of the first micro-nano structure layer, the second micro-nano structure layer and the third micro-nano structure layer, the functions of a quarter-wave plate and a full-space half-wave plate are realized in the same device. It can realize the conversion of linearly polarized light to left-hand circularly polarized light, right-hand circularly polarized light and orthogonal linearly polarized light in different frequency bands, which solves the limitation of the single function of traditional devices.

[0031] By utilizing the temperature-driven phase transition characteristics of the vanadium dioxide layer and controlling the ambient temperature to change the conductivity of vanadium dioxide, dynamic switching between transmission and reflection modes can be achieved. This allows the device to perform different polarization modulation functions under different operating modes, thus expanding the application flexibility of the device.

[0032] Based on the characteristics of the full-space half-wave plate, holographic imaging of incident light with arbitrary polarization was realized using the GS algorithm. This overcomes the limitation of the polarization state of incident light in traditional metasurface holographic imaging. It has important application value in polarization multiplexing imaging, three-dimensional holographic reconstruction and optical information encryption, and can be widely used in gas, liquid and biological sensing fields. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the terahertz LC resonant metasurface device of the present invention;

[0034] Figure 2 This is a top view schematic diagram of the first Wiener structure layer and the third micro / nano structure layer of the present invention;

[0035] Figure 3 This is a top view schematic diagram of the second micro / nano structure layer of the present invention;

[0036] Figure 4 This is a side view of the micro / nano structure layer of the present invention;

[0037] Figure 5 This is the electric field energy distribution diagram of the present invention under the reflection mode when x-polarized light is incident;

[0038] Figure 6 This is a magnetic field energy distribution diagram under the reflection mode when x-polarized light is incident, according to the present invention.

[0039] Figure 7 This is a graph showing the ellipticity of the emitted circularly polarized light when X-ray linearly polarized light is incident under the function of a quarter-wave plate according to the present invention.

[0040] Figure 8 This is a graph showing the polarization conversion efficiency of the emitted circularly polarized light when x-polarized light is incident under the function of a quarter-wave plate according to the present invention.

[0041] Figure 9 This is a polarization state diagram of the emitted left-handed circularly polarized light when x-linearly polarized light is incident under the function of a quarter-wave plate according to the present invention;

[0042] Figure 10 This is a polarization state diagram of the right-hand circularly polarized light emitted when x-linearly polarized light is incident under the function of a quarter-wave plate according to the present invention.

[0043] Figure 11 This is a graph showing the polarization conversion rate of reflected y-polarized light when x-polarized light is incident under the half-wave plate function of the present invention.

[0044] Figure 12 This is a graph showing the extinction ratio of reflected y-polarized light when x-polarized light is incident under the half-wave plate function of the present invention.

[0045] Figure 13 This is a polarization state diagram of the reflected y-polarized light when x-polarized light is incident under the function of a half-wave plate according to the present invention.

[0046] Figure 14 This is a graph showing the polarization conversion rate of transmitted y-polarized light when x-polarized light is incident under the half-wave plate function of the present invention.

[0047] Figure 15 This is a graph showing the extinction ratio of transmitted y-polarized light when x-polarized light is incident under the half-wave plate function of the present invention.

[0048] Figure 16 This is a polarization state diagram of transmitted y-polarized light when x-polarized light is incident under the function of a half-wave plate according to the present invention.

[0049] Figure 17 This invention provides a sequence of different target images for full-space holographic imaging.

[0050] Figure 18 This is the holographic imaging result of the corresponding image sequence in the full-space holographic imaging of the present invention;

[0051] exist Figures 1 to 18 In the diagram, the correspondence between component names or lines and the drawing numbers is as follows:

[0052] 1. Dielectric protective layer; 2. First micro / nano structure layer; 3. First dielectric layer; 4. Vanadium dioxide layer; 5. Negative structure metal layer; 6. Second dielectric layer; 7. Third micro / nano structure layer; 8. Third dielectric layer. Detailed Implementation

[0053] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0054] See Figures 1-4As shown, an embodiment of the present invention proposes a terahertz metasurface device capable of multi-polarization control, comprising a first dielectric layer 3, a second dielectric layer 6, and a third dielectric layer 8 stacked sequentially. A first micro / nano structure layer 2 is stacked on the first dielectric layer 3, a second micro / nano structure layer is stacked on the second dielectric layer 6, and a third micro / nano structure layer 7 is stacked on the third dielectric layer 8. The first micro / nano structure layer 2 and the third micro / nano structure layer 7 are identical, both exhibiting a Z-shaped structure. The second micro / nano structure layer includes a negative structure metal layer 5 stacked on the second dielectric layer 6 and a vanadium dioxide layer 4 located in the middle of the negative structure metal layer 5, the vanadium dioxide layer 4 exhibiting a cross-shaped structure. A dielectric protective layer 1 covers the first micro / nano structure layer 2. Specifically, in this embodiment, the stacking order from top to bottom is: dielectric protective layer 1, first micro / nano structure layer 2, first dielectric layer 3, second micro / nano structure layer, second dielectric layer 6, third micro / nano structure layer 7, and third dielectric layer 8. The dielectric protective layer 1 protects the first micro / nano structure layer 2 from external environmental corrosion and also serves as an impedance matching layer to reduce reflection loss. The first dielectric layer 3, the second dielectric layer 6, and the third dielectric layer 8 act as spacers to adjust the electromagnetic coupling strength between the micro / nano structure layers and form a resonant cavity structure to achieve multi-band polarization conversion.

[0055] The first micro / nano structure layer 2 and the third micro / nano structure layer 7 are made of gold, which has good conductivity and chemical stability, and can excite strong LC resonance in the terahertz band. The negative structure metal layer in the second micro / nano structure layer is also made of gold; in this embodiment, the gold used has a conductivity of 4.56 × 10⁻⁶. 7 The S / m, while the central cruciform vanadium dioxide layer 4 is made of vanadium dioxide material. Vanadium dioxide material has significant temperature-driven phase transition characteristics, transforming from an insulating phase to a metallic phase at approximately 68℃, thereby achieving dynamic switching between transmission and reflection modes.

[0056] The first dielectric layer 3, the second dielectric layer 6, the third dielectric layer 8, and the dielectric protective layer 1 are all made of cyclic olefin copolymer (COC). In this embodiment, the relative permittivity of the COC used is 2.1 + 0.006i, where i is the imaginary unit, satisfying i 2 = -1. COC has extremely low absorption loss and a stable dielectric constant in the terahertz band, which can effectively support micro and nanostructures and reduce energy dissipation.

[0057] To achieve precise polarization control, the dimensional parameters of the micro / nano structure layers were optimized. The first micro / nano structure layer 2 and the third micro / nano structure layer 7 have a rotation angle γ of 55° relative to the second dielectric layer 6 or the third dielectric layer 8. This rotation angle allows the first micro / nano structure layer 2, after periodic alignment, to form an equivalent capacitance with adjacent micro / nano structures, effectively exciting LC resonance and introducing a 180° phase change, which is key to realizing the functions of a quarter-wave plate and a half-wave plate.

[0058] The period lengths of the first micro / nano structure layer 2, the second micro / nano structure layer, and the third micro / nano structure layer 7 along the x and y directions are P, and the period length P should be greater than the dimensions of the first micro / nano structure layer 2 and the third micro / nano structure layer 7. Therefore, P is set to 50 μm. This periodic dimension is smaller than the operating wavelength (the wavelength in the terahertz band is about 60-130 μm), which satisfies the subwavelength structure condition, allowing the device to operate within the approximate range of the equivalent medium.

[0059] The specific parameters of the first micro / nano structure layer 2 and the third micro / nano structure layer 7 are as follows: height and length It is 32 μm long, and the outer straight arm is 32 μm long. It is 32 μm long, and the inner straight arm is 32 μm long. It is 26 μm long and the inclined arm is long. The Z-shaped structure has a diameter of 24 μm, a thickness t1 of 0.2 μm, and a rotation angle γ of 55°. These dimensions, optimized through simulation, enable a strong LC resonance at a frequency of 2.61 THz. The electric field energy is mainly concentrated at the corners and endpoints of the Z-shaped structure, interacting with adjacent Z-shaped structures and exhibiting capacitive characteristics. The magnetic field energy is mainly concentrated at the straight and slanted arms, exhibiting inductive characteristics. The LC resonance produces a 180° phase abrupt change at 2.61 THz, thus achieving different linear-to-circular polarization transitions on either side of the resonance frequency.

[0060] The parameters of the second micro / nano structure layer are: long side length c1 is 42 μm, short side length c2 is 10 μm, and thickness t2 is 0.5 μm. The cross-shaped vanadium dioxide layer 4 and the surrounding negative structure metal layer 5 together constitute a tunable resonant unit. By controlling the conductivity of the vanadium dioxide layer 4, the electromagnetic response of the layer can be changed, thereby realizing the switching between transmission mode and reflection mode.

[0061] The thicknesses of each dielectric layer are as follows: the first dielectric layer 3 has a thickness l2 of 8 μm, the second dielectric layer 6 has a thickness l3 of 9 μm, the third dielectric layer 8 has a thickness l4 of 3 μm, and the dielectric protective layer 1 has a thickness l1 of 3 μm. These thickness values ​​are chosen to achieve optimal balance in electromagnetic coupling between the layers while ensuring the overall mechanical strength of the device.

[0062] The electrical conductivity of the vanadium dioxide layer 4 is w p The mode switching is based on changes in the external ambient temperature. When w p When the value of is 10 S / m, the vanadium dioxide layer 4 is in the insulating phase, and the device operates in transmission mode; when w p The value is 2×10 5 At a speed of S / m, the vanadium dioxide layer 4 is in the metallic phase, and the device operates in reflection mode. This characteristic can be used to precisely control the propagation path of terahertz waves.

[0063] When the vanadium dioxide layer 4 is in reflection mode, the terahertz metasurface device operates simultaneously as a quarter-wave plate and a half-wave plate; when the vanadium dioxide layer 4 is in transmission mode, the terahertz metasurface device operates as a half-wave plate. Specifically, in reflection mode, when X-ray polarized light is incident, the device outputs left-handed circularly polarized light (ellipticity greater than 0.99, average efficiency 87.92%) in the 2.30 THz~2.34 THz frequency band and right-handed circularly polarized light (ellipticity less than -0.99, average efficiency 94.14%) in the 3.13 THz~4.76 THz frequency band, while simultaneously achieving orthogonal linear polarization conversion (polarization conversion rate greater than 0.9, peak extinction ratio 26.46 dB) in the mid-frequency band of 2.50 THz~2.75 THz. In transmission mode, the device achieves orthogonal linear polarization conversion (polarization conversion rate greater than 0.9, peak extinction ratio 12.54 dB) in the 2.07 THz~2.24 THz frequency band.

[0064] The terahertz metasurface device constructed using the above parameters and structural stacking operates in the frequency range of 2.30 THz to 4.71 THz. During detection, when the terahertz metasurface device is arranged in a periodic unit configuration, it can function as a quarter-wave plate and a half-wave plate in reflection mode, and as a half-wave plate in transmission mode. The incident beam is X-polarized light and perpendicular to the terahertz metasurface device. Holographic imaging based on the Gerchberg–Saxton (GS) algorithm can be realized on the basis of a full-space half-wave plate, with the incident beam being arbitrarily polarized light and perpendicular to the terahertz metasurface device.

[0065] The conductivity of the vanadium dioxide layer 4 can be controlled by changing the ambient temperature, enabling mode switching between transmission and reflection modes. This characteristic allows for precise control of light propagation. In the insulating phase, light absorption and reflection are weak, and the terahertz metasurface device operates in transmission mode; in the metallic phase, it exhibits high light absorption and reflection, and the terahertz metasurface device operates in reflection mode.

[0066] Terahertz metasurface devices achieve polarization switching across three frequency bands in reflection mode by exciting LC resonance. (See also...) Figure 5As shown in the figure, the gray levels from light to dark represent the electric field intensity from low to high. The electric field is mainly concentrated at the corners and endpoints of the first micro / nano structure layer 2. The electric field intensity far from the micro / nano structure region is close to 0 V / m, while the electric field intensity at the aforementioned local locations increases significantly, with a local maximum of approximately 5 × 10⁻⁶ V / m. 6 V / m. Interacting with adjacent basic units, it exhibits capacitive characteristics; see [link to relevant documentation]. Figure 6 As shown in the figure, the gray levels from light to dark represent the magnetic field strength from low to high. The magnetic field energy is mainly concentrated at the straight and inclined arms of the first micro / nano structure layer 2. The magnetic field strength far from the micro / nano structure region is close to 0 A / m, while the local magnetic field strength near the metal arm can reach a maximum of 1 × 10⁻⁶ A / m. 5 A / m. The equivalent capacitance and equivalent inductance effects described above together form an LC resonance, thus causing a 180° phase abrupt change in the reflection phase, which is achieved at the resonant frequency. x Orthogonal polarization conversion of linear polarization is achieved, with different linear-to-circular polarization conversions on either side of the resonant frequency. This allows for the realization of a designable multi-polarization-conversion terahertz metasurface using LC resonance.

[0067] When terahertz metasurface devices function as quarter-terahertz waveplates, the conversion process from linearly polarized light to left-handed or right-handed circularly polarized light can be described using Stokes parametric notation: ; ; ; ; Among them, |R xx |and|R yx | represents the reflection coefficients for x- and y-polarized incident light. and This represents the reflection phases of x- and y-polarized light when incident with x-polarized light, and the phase difference between them. S0 represents the intensity of polarized light, S1 describes the linear polarization state along the x or y direction, S2 describes the linear polarization state along the 45° or -45° direction, and S3 represents the degree of circular polarization. See also Figure 7 As shown, this is a graph depicting the ellipticity of the emitted circularly polarized light when X-rays are incident under the function of a quarter-wave plate. Ellipticity is defined. At this point, in the 2.30 THz to 2.34 THz band, the ellipticity is greater than 0.99, resulting in well-emitted left-handed circularly polarized light, with the best performance at 2.31 THz; in the 3.13 THz to 4.76 THz band, the ellipticity is less than -0.99, resulting in well-emitted right-handed circularly polarized light, with the best performance at 4.56 THz. See also Figure 8As shown, the polarization conversion efficiency curve of the emitted circularly polarized light when X-rays are incident under quarter-wave plate function is defined. In the 2.30 THz to 2.34 THz band, the calculated average efficiency is 87.92%; in the 3.13 THz to 4.76 THz band, the calculated average efficiency is 94.14%. See also... Figure 9 As shown, when linearly polarized X-rays are incident under quarter-wave plate conditions, the polarization state diagram of the emitted circularly polarized light is obtained, yielding the polarization state diagram of left-handed circularly polarized light at 2.31 THz, which is close to the polarization state of left-handed circularly polarized light; see [link to relevant documentation]. Figure 10 As shown, the polarization state diagram of right-hand circularly polarized light at 4.56 THz is obtained, which is very close to the polarization state of ideal right-hand circularly polarized light.

[0068] When terahertz metasurface devices realize the function of a full-space terahertz half-wave plate, the conversion process from x-polarized light to y-polarized light can be evaluated by polarization conversion rate and extinction ratio. See also... Figure 11 As shown, the polarization conversion efficiency curve of the emitted y-polarized light when x-polarized light is incident under the function of a half-wave plate is defined. In the 2.50 THz to 2.75 THz band, PCR R A value greater than 0.9 results in well-polarized emitted light, with the best performance observed at 2.60 THz; see [link / reference]. Figure 12 The figure shows the extinction ratio curve of the emitted y-polarized light when x-polarized light is incident under half-wave plate function. The extinction ratio is defined as follows. It reaches a peak of 26.46 dB at 2.60 THz, exhibiting an ideal y-polarization state; see [link / reference]. Figure 13 As shown, when x-polarized light is incident under half-wave plate conditions, the polarization state diagram of the reflected y-polarized light is obtained, yielding a polarization state diagram of linearly polarized light at 2.60 THz, which is very close to the polarization state diagram of perfectly y-polarized light. See also... Figure 14 As shown, this is a graph illustrating the polarization conversion efficiency of the emitted y-polarized light when x-polarized light is incident under the function of a transmission half-wave plate. The polarization conversion rate is defined as follows. , where |T xx | and | T yx | represents the transmission coefficient for x- and y-polarized incident light. In the 2.07 THz to 2.24 THz band, PCR T A value greater than 0.9 results in well-polarized emitted light, with the best performance observed at 2.60 THz; see [link / reference]. Figure 15 As shown, this is a graph depicting the extinction ratio of the emitted y-polarized light when x-polarized light is incident under half-wave plate conditions. The extinction ratio is defined as follows: It reaches a peak value of 12.54 dB at 2.18 THz, exhibiting a relatively ideal y-polarization state; see [link to relevant documentation]. Figure 16 As shown, when x-polarized light is incident under half-wave plate function, the polarization state diagram of transmitted y-polarized light is obtained, which is close to the polarization state of y-polarized light at 2.18 THz.

[0069] Terahertz metasurface devices achieve holographic imaging with arbitrary polarization incident waves based on the functionality of a full-space terahertz half-wave plate. A reflective metasurface is used for illustration, and the same theory applies to a transmission metasurface. For an incident wave with arbitrary polarization, the reflected electric field E... r It can be represented by orthogonal basis vectors of x-polarization and y-polarization as follows: + ,in and Represents the components of the incident electric field in the x and y directions, |R xx |and|R yx | represents the reflection coefficients for x- and y-polarized incident light. and Represents the reflection phases of x- and y-polarized incident light, |R xy |and|R yy | represents the reflection coefficients for x and y polarization when incident with y-polarized light. and This represents the reflection phase of x- and y-polarized light when the light is incident with y-polarization. and Represents the unit vector in the x and y directions. and This represents the reflection phase of x- and y-polarized light when the light is incident with y-polarization, where i is the imaginary unit and satisfies i 2 =﹣1, Represents the phase factor. Under ideal half-wave plate conditions, the orthogonal reflection coefficient |R xx |=|R yy |=0, therefore the formula can be further rewritten as After the basic unit of the micro / nano structure is rotated 90°, the reflected output electric field is... Terahertz metasurface devices satisfy , , and ,in and The coefficients representing the y-polarized incident x-polarized reflection and x-polarized incident y-polarized reflection after the basic unit of the micro / nano structure is rotated 90° are given. and This represents the phase of y-polarized incident x-polarized reflection and x-polarized incident y-polarized reflection after the basic unit of the micro / nano structure is rotated 90°. Therefore, the output electric field satisfies This allows for a 180° phase transition in the reflected electric field, which can then be used as a basis vector to achieve a 180° phase difference for arbitrary polarization. The first micro / nano structure layer 2 and the third micro / nano structure layer 7, rotated at angles of 55° and 145° respectively, form a 1-bit encoding unit. (See also...) Figure 17 As shown, the character "NEPU" is set as the expected far-field imaging target. The GS iterative algorithm is used to converge after multiple iterations to obtain the phase arrangement sequence corresponding to the metasurface array. The coding units are then arranged in the array according to the phase sequence. Elliptically polarized light is used. As the incident excitation, where the superscript T denotes transpose and i is the imaginary unit, satisfying i 2 =﹣1. The full-space holographic imaging performance of the designed metasurface was simulated and verified, and the results are as follows: Figure 18 As shown in the figure, the grayscale represents the normalized electric field intensity; the darker the grayscale, the greater the corresponding normalized electric field intensity. In the transmission space, the target patterns "N" and "E" can be reconstructed respectively; in the reflection space, the target patterns "P" and "U" can be reconstructed respectively. The main outlines and feature regions of the four target letters can be clearly distinguished, and the imaging energy is mainly concentrated in the preset target area. This design can achieve holographic imaging under arbitrary polarization incident light, overcoming the limitation of single incident light on the metasurface in traditional holographic imaging.

[0070] Therefore, we can conclude that terahertz metasurface devices can achieve effective multi-polarization manipulation. x When linearly polarized incident, LC resonance can be excited in reflection mode to simultaneously achieve left-handed circular polarization. y Linearly polarized and right-hand circularly polarized light are emitted, achieving transmission mode. x Orthogonal polarization conversion of linearly polarized light; at the same time, terahertz metasurface devices can achieve effective arbitrary polarization holographic imaging based on a full-space half-wave plate.

[0071] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0072] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0073] It will be apparent to those skilled in the art that the present 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 its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A terahertz metasurface device capable of multi-polarization modulation, characterized in that: It includes a first dielectric layer (3), a second dielectric layer (6) and a third dielectric layer (8) stacked in sequence. A first micro-nano structure layer (2) is stacked on the first dielectric layer (3), a second micro-nano structure layer is stacked on the second dielectric layer (6), and a third micro-nano structure layer (7) is stacked on the third dielectric layer (8). The first micro-nano structure layer (2) is the same as the third micro-nano structure layer (7), both having a Z-shaped structure; The second micro / nano structure layer includes a negative structure metal layer (5) stacked on the second dielectric layer (6) and a vanadium dioxide layer (4) located in the middle of the negative structure metal layer (5), the vanadium dioxide layer (4) having a cross-shaped structure; The first micro / nano structure layer (2) is covered with a dielectric protective layer (1).

2. The terahertz metasurface device capable of multi-polarization control according to claim 1, characterized in that: The first micro / nano structure layer (2) and the third micro / nano structure layer (7) are made of gold, with an electrical conductivity of 4.56 × 10⁻⁶. 7 S / m.

3. A terahertz metasurface device capable of multi-polarization control according to claim 2, characterized in that: The first dielectric layer (3), the second dielectric layer (6), the third dielectric layer (8), and the dielectric protective layer (1) are all made of cyclic olefin copolymers with a relative permittivity of 2.1 + 0.006i, where i is the imaginary unit, satisfying i 2 =﹣1.

4. A terahertz metasurface device capable of multi-polarization control according to any one of claims 1-3, characterized in that: The first micro / nano structure layer (2) and the third micro / nano structure layer (7) have a rotation angle γ relative to the second dielectric layer (6) or the third dielectric layer (8), where γ is 55°.

5. A terahertz metasurface device capable of multi-polarization control according to claim 4, characterized in that: The period lengths of the first micro-nano structure layer (2), the second micro-nano structure layer and the third micro-nano structure layer (7) along the x and y directions are P, where P is 50 μm.

6. A terahertz metasurface device capable of multi-polarization control according to claim 5, characterized in that: The parameters of the first micro / nano structure layer (2) and the third micro / nano structure layer (7) include: Overall height is , It is 32 μm; The length of the outer straight arm is , It is 32 μm; The length of the inner straight arm is , It is 26 μm; The height of the slant arm is , It is 24 μm; The thickness is t1, which is 0.2 μm.

7. A terahertz metasurface device capable of multi-polarization control according to claim 5, characterized in that: The parameters of the second micro / nano structure layer include: The length of the longer side is c1, and c1 is 42 μm; The shorter side has a length of c2, and c2 is 10 μm. The thickness is t2, which is 0.5 μm.

8. A terahertz metasurface device capable of multi-polarization control according to claim 5, characterized in that: The thickness of the first dielectric layer (3) is l2, and l2 is 8 μm; The thickness of the second dielectric layer (6) is l3, and l3 is 9 μm; The thickness of the third dielectric layer (8) is l4, and l4 is 3 μm; The thickness of the dielectric protective layer (1) is l1, and l1 is 3 μm.

9. A terahertz metasurface device capable of multi-polarization control according to claim 5, characterized in that: The conductivity of the vanadium dioxide layer (4) is w p Based on changes in the external ambient temperature, when w p When the value of is 10 S / m, the vanadium dioxide layer (4) is in transmission mode; when w p The value is 2×10 5 At S / m, the vanadium dioxide layer is in reflection mode.

10. A terahertz metasurface device capable of multi-polarization control according to claim 9, characterized in that: When the vanadium dioxide layer (4) is in reflection mode, the terahertz metasurface device operates in a simultaneous quarter-wave plate and half-wave plate mode; when the vanadium dioxide layer (4) is in transmission mode, the terahertz metasurface device operates in a half-wave plate mode.

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