A U-shaped metamaterial and a preparation method thereof

Abstract

The application relates to the technical field of metamaterials, in particular to a U-shaped metamaterial and a preparation method thereof. The method comprises the following steps: rotatingly coating polyamide acid on a base sheet to obtain a first pre-prepared layer, and performing thermal imidization treatment to obtain a bottom medium layer made of polyimide; obtaining a U-shaped metal layer on the upper surface of the bottom medium layer; rotatingly coating polyamide acid on the bottom medium layer to obtain a second pre-prepared layer, and performing thermal imidization treatment to obtain a middle medium layer made of polyimide; obtaining another U-shaped metal layer on the surface of the middle medium layer; rotatingly coating polyamide acid on the middle medium layer provided with the U-shaped metal layer to obtain a third pre-prepared layer, and performing thermal imidization treatment to obtain a top medium layer made of polyimide, and then obtaining a period unit; and arranging the period units periodically to form the U-shaped metamaterial. The application provides a preparation method of a metamaterial capable of changing the polarization state of electromagnetic waves in the terahertz wave band.

Description

Technical Field

[0001] This invention relates to the field of metamaterials technology, and in particular to a U-shaped metamaterial and its preparation method. Background Technology

[0002] "Metamaterials" are a new type of artificial electromagnetic material capable of manipulating electromagnetic waves at subwavelength scales, possessing unique electromagnetic properties not found in natural materials. Unlike materials in nature, the electromagnetic properties of artificial electromagnetic materials depend primarily on their unique structural design, rather than their intrinsic chemical properties. Therefore, artificial electromagnetic materials can break through specific natural laws, thereby achieving electromagnetic phenomena that are impossible with natural materials, such as unidirectional transmission of electromagnetic waves, negative refractive index, and anomalous reflection.

[0003] In existing technologies, metamaterials can be used to alter the polarization state of electromagnetic waves in a target band. However, there is a lack of metamaterials capable of altering the polarization state of electromagnetic waves in the terahertz band. Summary of the Invention

[0004] This invention provides a U-shaped metamaterial and its preparation method, which can provide a metamaterial capable of changing the polarization state of electromagnetic waves in the terahertz band.

[0005] In a first aspect, embodiments of the present invention provide a method for preparing a U-shaped metamaterial, comprising:

[0006] Polyamic acid is spin-coated onto a substrate to obtain a first preform layer. The first preform layer is then subjected to thermal imidization treatment to obtain a bottom dielectric layer made of polyimide.

[0007] A U-shaped metal layer is obtained on the upper surface of the bottom dielectric layer using photolithography.

[0008] Polyamic acid is spin-coated onto the bottom dielectric layer on which the U-shaped metal layer is disposed to obtain a second preform layer. The second preform layer is subjected to the thermal imidization treatment to obtain an intermediate dielectric layer made of polyimide.

[0009] Another U-shaped metal layer is obtained on the surface of the intermediate dielectric layer away from the bottom dielectric layer using photolithography.

[0010] Polyamic acid is spin-coated onto the intermediate dielectric layer on which the U-shaped metal layer is disposed to obtain a third prefabricated layer. The third prefabricated layer is subjected to the thermal imidization treatment to obtain a top dielectric layer of polyimide material. A cuboid periodic unit is obtained, including the bottom dielectric layer, the intermediate dielectric layer, the top dielectric layer and the two U-shaped metal layers. The periodic unit includes two square faces. The U-shaped metal layer includes two parallel first metal strips and a second metal strip perpendicular to the first metal strips. The two ends of the second metal strip are respectively connected to the endpoints of the two first metal strips on the same side.

[0011] The periodic units are periodically arranged along two directions containing the edges of adjacent units that are perpendicular to each other to form a U-shaped metamaterial;

[0012] The substrate is fixed by positioning holes on the substrate, ensuring that the two U-shaped metal layers are strictly aligned vertically.

[0013] In one possible design, the side length of the square face of the periodic unit is 40–50 μm.

[0014] In one possible design, the spin-coating of polyamic acid onto a square substrate to obtain a first preform layer, followed by thermal imidization of the first preform layer to obtain a polyimide bottom dielectric layer, includes:

[0015] Polyamic acid is spin-coated onto a square substrate at a speed of 700 rpm to obtain a first pre-layer with a thickness of 6-10 μm. The first pre-layer is then subjected to thermal imidization treatment to obtain a bottom dielectric layer with a thickness of 6-10 μm made of polyimide.

[0016] In one possible design, the spin-coating of polyamic acid onto the bottom dielectric layer where the U-shaped metal layer is disposed to obtain a second preform layer, and the thermal imidization treatment of the second preform layer to obtain an intermediate dielectric layer made of polyimide, includes:

[0017] Polyamic acid is applied to the bottom dielectric layer on which the U-shaped metal layer is disposed at a speed of 1100 rpm to obtain a second preform layer with a thickness of 12-15 μm. The second preform layer is then subjected to thermal imidization treatment to obtain an intermediate dielectric layer with a thickness of 12-15 μm and made of polyimide.

[0018] In one possible design, the spin-coating of polyamic acid onto the intermediate dielectric layer where the U-shaped metal layer is disposed to obtain a third preform layer, and the thermal imidization treatment of the third preform layer to obtain a top dielectric layer of polyimide material, includes:

[0019] Polyamic acid is applied to the intermediate dielectric layer on which the U-shaped metal layer is disposed at a speed of 2600 rpm to obtain a third prefabricated layer with a thickness of 3-7 μm. The third prefabricated layer is subjected to thermal imidization treatment to obtain a top dielectric layer of polyimide with a thickness of 3-7 μm.

[0020] In one possible design, the thickness of the U-shaped metal layer is 180–220 nm, the width of the first metal strip and the second metal strip are both 7–9 μm, the length direction of the U-shaped metal layer is the same as the length direction of the first metal strip, the width direction of the U-shaped metal layer is the same as the length direction of the second metal strip, the length of the U-shaped metal layer is 32–34 μm, and the width is 30–32 μm.

[0021] In one possible design, the material used to prepare the U-shaped metal layer includes gold.

[0022] In one possible design, the thermal imidization treatment includes:

[0023] Bake at 100–110℃ for 8–12 minutes;

[0024] Bake at 150–170℃ for 25–35 minutes;

[0025] Increase the temperature to 280–320°C at a rate of 3°C / min and bake for 50–70 minutes.

[0026] In one possible design, the thermal imidization treatment is carried out in a nitrogen atmosphere.

[0027] Secondly, embodiments of the present invention also provide a U-shaped metamaterial, which is prepared by any one of the methods described in the first aspect.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] In this embodiment, the metamaterial is composed of multiple micron-sized periodic units. The periodic units of the U-shaped metamaterial provided by this invention are multi-layered structures, and the periodic units are prepared layer by layer. Specifically, a bottom dielectric layer is first prepared, which is a polyimide layer with a thickness of micrometers. Micrometer-thick polyamic acid is prepared on a square substrate using spin coating. Then, thermal imidization is performed to dehydrate the polyamic acid, resulting in the bottom dielectric layer made of polyimide. Next, a metal sheet layer is placed on the bottom dielectric layer, and the metal sheet is shaped using photolithography to obtain a U-shaped metal layer. Then, polyamic acid is spin-coated again on the surface of the bottom dielectric layer with the U-shaped metal layer. Due to its fluidity, the polyamic acid encapsulates the U-shaped metal layer. After thermal imidization, the polyamic acid gradually solidifies and dehydrates to form a flexible solid polyimide layer, similar to the formation process of amber. The U-shaped metal layer encapsulates the bottom and middle dielectric layers. Similarly, another U-shaped metal layer and a top dielectric layer are prepared, ultimately obtaining micrometer-thick periodic units. These periodic units are then arranged periodically to form a metamaterial.

[0030] In this embodiment, since magneto-optical materials with gyromagnetic or gyroelectric responses in the terahertz band are lacking in nature, this invention provides an artificial U-shaped metamaterial capable of exhibiting gyromagnetic or gyroelectric responses in the terahertz band. The U-shaped metamaterial provided by this invention is composed of multiple periodically arranged periodic units. The cross-section of each periodic unit is square, and the periodic units are arranged along two adjacent perpendicular sides of the square with a period equal to the side length to form the metamaterial. Each periodic unit consists of a top dielectric layer, an intermediate dielectric layer, and a bottom dielectric layer stacked sequentially along the thickness direction. U-shaped metal layers are disposed on the surfaces of the intermediate and bottom dielectric layers facing the top dielectric layer, and these two U-shaped metal layers are perfectly aligned vertically. When terahertz electromagnetic waves pass through the periodic unit with the U-shaped metal layers, the metamaterial can change the polarization state of the terahertz electromagnetic waves. Specifically, the U-shaped metal layer includes two parallel first metal strips and a second metal strip connecting the two first metal strips at the same endpoint. When the terahertz electromagnetic wave passes through the metamaterial, the electric field component of the terahertz electromagnetic wave along the extension direction of the first metal strips increases in phase, thereby changing the polarization state of the terahertz electromagnetic wave. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of a terahertz transmission isolation system provided in an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of a polarizer and metamaterial combination provided in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of a polarizer provided in an embodiment of the present invention;

[0035] Figure 4 This is a side cross-sectional structural diagram of a periodic unit provided in an embodiment of the present invention;

[0036] Figure 5 This is a top view schematic diagram of a periodic unit provided in an embodiment of the present invention;

[0037] Figure 6 This is an insertion loss diagram of a terahertz transmission isolation system at different incident angles provided in an embodiment of the present invention;

[0038] Figure 7 This is an isolation diagram of a terahertz transmission isolation system with different incident angles provided in an embodiment of the present invention.

[0039] In the picture:

[0040] 1-Wire grid fixing ring;

[0041] 2-line grid;

[0042] 3-U-shaped metamaterials;

[0043] 4-Metamaterial retaining ring;

[0044] 5-Top dielectric layer;

[0045] 6-Intermediate dielectric layer;

[0046] 7- Bottom dielectric layer;

[0047] 8-U-shaped metal layer;

[0048] 9-First metal strip;

[0049] 10 - Second metal strip;

[0050] 100 - Reflection unit. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0052] In the description of the embodiments of the present invention, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; unless otherwise specified or stated, the term "multiple" refers to two or more; the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0053] In this specification, it should be understood that the directional terms such as "upper" and "lower" used in the description of the embodiments of the present invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of the present invention. Furthermore, in the context, it should also be understood that when it is mentioned that one element is connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected to the other element "upper" or "lower" through an intermediate element.

[0054] like Figure 4 , 5 As shown, this embodiment of the invention provides a method for preparing a U-shaped metamaterial, comprising:

[0055] Polyamic acid is spin-coated onto a substrate to obtain a first preform layer. The first preform layer is then subjected to thermal imidization treatment to obtain a bottom dielectric layer made of polyimide.

[0056] A U-shaped metal layer is obtained on the upper surface of the bottom dielectric layer using photolithography.

[0057] Polyamic acid is spin-coated onto the bottom dielectric layer with a U-shaped metal layer to obtain a second preform layer. The second preform layer is then subjected to thermal imidization treatment to obtain an intermediate dielectric layer made of polyimide.

[0058] Another U-shaped metal layer is obtained on the surface of the intermediate dielectric layer away from the bottom dielectric layer using photolithography.

[0059] Polyamic acid is spin-coated onto an intermediate dielectric layer with a U-shaped metal layer to obtain a third prefabricated layer. The third prefabricated layer is then subjected to thermal imidization to obtain a top dielectric layer made of polyimide. This results in a cuboid periodic unit comprising a bottom dielectric layer, an intermediate dielectric layer, a top dielectric layer, and two U-shaped metal layers. The periodic unit includes two square faces. The U-shaped metal layer includes two parallel first metal strips and a second metal strip perpendicular to the first metal strips. The two ends of the second metal strip are respectively connected to the endpoints of the two first metal strips on the same side.

[0060] A U-shaped metamaterial is formed by periodically arranging periodic units along two directions where the edges of adjacent units are perpendicular to each other;

[0061] The substrate is fixed by positioning holes on the substrate, ensuring that the two H-shaped metal layers are strictly aligned vertically.

[0062] In this embodiment, the metamaterial is composed of multiple micron-sized periodic units. The periodic units of the U-shaped metamaterial provided by this invention are multi-layered structures, and the periodic units are prepared layer by layer. Specifically, a bottom dielectric layer is first prepared, which is a polyimide layer with a thickness of micrometers. Micrometer-thick polyamic acid is prepared on a square substrate using spin coating. Then, thermal imidization is performed to dehydrate the polyamic acid, resulting in the bottom dielectric layer made of polyimide. Next, a metal sheet layer is placed on the bottom dielectric layer, and the metal sheet is shaped using photolithography to obtain a U-shaped metal layer. Then, polyamic acid is spin-coated again on the surface of the bottom dielectric layer with the U-shaped metal layer. Due to its fluidity, the polyamic acid encapsulates the U-shaped metal layer. After thermal imidization, the polyamic acid gradually solidifies and dehydrates to form a flexible solid polyimide layer, similar to the formation process of amber. The U-shaped metal layer encapsulates the bottom and middle dielectric layers. Similarly, another U-shaped metal layer and a top dielectric layer are prepared, ultimately obtaining micrometer-thick periodic units. These periodic units are then arranged periodically to form a metamaterial.

[0063] In this embodiment, since magneto-optical materials with gyromagnetic or gyroelectric responses in the terahertz band are lacking in nature, this invention provides an artificial U-shaped metamaterial capable of exhibiting gyromagnetic or gyroelectric responses in the terahertz band. The U-shaped metamaterial provided by this invention is composed of multiple periodically arranged periodic units. The cross-section of each periodic unit is square, and the periodic units are arranged along two adjacent perpendicular sides of the square with a period equal to the side length to form the metamaterial. Each periodic unit consists of a top dielectric layer, an intermediate dielectric layer, and a bottom dielectric layer stacked sequentially along the thickness direction. U-shaped metal layers are disposed on the surfaces of the intermediate and bottom dielectric layers facing the top dielectric layer, and these two U-shaped metal layers are perfectly aligned vertically. When terahertz electromagnetic waves pass through the periodic unit with the U-shaped metal layers, the metamaterial can change the polarization state of the terahertz electromagnetic waves. Specifically, the U-shaped metal layer includes two parallel first metal strips and a second metal strip connecting the two first metal strips at the same endpoint. When the terahertz electromagnetic wave passes through the metamaterial, the electric field component of the terahertz electromagnetic wave along the extension direction of the first metal strips increases in phase, thereby changing the polarization state of the terahertz electromagnetic wave.

[0064] It should be noted that after obtaining the top dielectric layer, hydrofluoric acid can be used to detach the periodic cells from the substrate, and the substrate material can include silicon.

[0065] In some embodiments of the present invention, the side length of the square face of the periodic unit is 40 to 50 μm.

[0066] In this embodiment, the side length of the square face of the periodic unit is 40–50 μm. The parameters of the periodic unit can affect the performance of the metamaterial; when the parameters are within the above range, the metamaterial exhibits excellent effect in altering the polarization state of terahertz waves.

[0067] In some embodiments of the present invention, polyamic acid is spin-coated onto a square substrate to obtain a first preform layer, and the first preform layer is subjected to thermal imidization treatment to obtain a bottom dielectric layer of polyimide material, comprising:

[0068] Polyamic acid was spin-coated onto a square substrate at a speed of 700 rpm to obtain a first pre-layer with a thickness of 6–10 μm. The first pre-layer was then subjected to thermal imidization treatment to obtain a bottom dielectric layer with a thickness of 6–10 μm made of polyimide.

[0069] In this embodiment, the rotational speed of spin coating is negatively correlated with the thickness of the resulting thin layer.

[0070] In some embodiments of the present invention, polyamic acid is spin-coated onto a bottom dielectric layer having a U-shaped metal layer to obtain a second preform layer. The second preform layer is then subjected to thermal imidization treatment to obtain an intermediate dielectric layer made of polyimide, comprising:

[0071] Polyamic acid is applied to the bottom dielectric layer with a U-shaped metal layer at a rotation speed of 1100 rpm to obtain a second prefabricated layer with a thickness of 12-15 μm. The second prefabricated layer is then subjected to thermal imidization treatment to obtain an intermediate dielectric layer with a thickness of 12-15 μm and made of polyimide.

[0072] In this embodiment, a thicker layer can be obtained by either a single spin coating or two spin coating processes.

[0073] In some embodiments of the present invention, polyamic acid is spin-coated onto an intermediate dielectric layer having a U-shaped metal layer to obtain a third preform layer. The third preform layer is then subjected to thermal imidization treatment to obtain a top dielectric layer made of polyimide, comprising:

[0074] Polyamic acid was spin-coated onto the intermediate dielectric layer with a U-shaped metal layer at a speed of 2600 rpm to obtain a third prefabricated layer with a thickness of 3-7 μm. The third prefabricated layer was then subjected to thermal imidization treatment to obtain a top dielectric layer with a thickness of 3-7 μm made of polyimide.

[0075] In this embodiment, the rotational speed of spin coating is negatively correlated with the thickness of the resulting thin layer.

[0076] In some embodiments of the present invention, the thickness of the U-shaped metal layer is 180-220 nm, the width of the first metal strip and the second metal strip are both 7-9 μm, the length direction of the U-shaped metal layer is the same as the length direction of the first metal strip, the width direction of the U-shaped metal layer is the same as the length direction of the second metal strip, the length of the U-shaped metal layer is 32-34 μm, and the width is 30-32 μm.

[0077] In this embodiment, a Cr layer can be deposited on the Au layer using sputtering deposition and a lift-off process. For example, it can be a metal layer with a Cr / Au ratio of 10 / 200 nm. The thickness of the U-shaped metal layer is 180–220 nm. The widths of the first and second metal strips are both 7–9 μm. The length direction of the U-shaped metal layer is the same as the length direction of the first metal strip, and the width direction is the same as the length direction of the second metal strip. The length of the U-shaped metal layer is 32–34 μm, and the width is 30–32 μm. The parameters of the U-shaped metal layer can affect the performance of the metamaterial. When the parameters are within the above range, the metamaterial exhibits excellent effects in altering the polarization state of terahertz waves.

[0078] In some embodiments of the present invention, the material used to prepare the U-shaped metal layer includes gold.

[0079] In this embodiment, gold possesses excellent and stable physicochemical properties, is an excellent conductor, and exhibits superior processability. Choosing gold as the material for preparing the U-shaped metal layer can further enhance the performance of the metamaterial and also facilitates its fabrication.

[0080] In some embodiments of the present invention, the thermal imidization treatment includes:

[0081] Bake at 100–110℃ for 8–12 minutes;

[0082] Bake at 150–170℃ for 25–35 minutes;

[0083] Increase the temperature to 280–320°C at a rate of 3°C / min and bake for 50–70 minutes.

[0084] In this embodiment, the polyamic acid is first baked at 100-110°C for 8-12 minutes to remove some of the solvent and raise the temperature; the baking is carried out in two stages to prevent excessive temperature changes from affecting imidization.

[0085] In some embodiments of the present invention, the thermal imidization treatment is carried out in a nitrogen atmosphere.

[0086] In this embodiment, nitrogen is low in cost, and its introduction is used to remove oxygen, thereby increasing the effectiveness and rate of the thermal imidization process. Of course, thermal imidization can also be performed in an atmospheric environment, but an oxygen-free environment is preferred.

[0087] This invention also provides a U-shaped metamaterial, which is prepared by any of the methods described above.

[0088] In this embodiment of the invention, polyimide is flexible, has insulating properties, is manufactured using mature processes, is easy to process, and is also a good medium for propagating terahertz electromagnetic waves.

[0089] like Figure 1 , 2 As shown in Figure 3, this embodiment of the invention also provides a terahertz transmission isolation system, based on any one of the U-shaped metamaterials mentioned above, wherein the system sequentially includes a polarizer, a U-shaped metamaterial, and a reflective unit;

[0090] The polarizer includes a wire grid, which consists of multiple parallel lines in the same plane. Each line of the wire grid is parallel to the diagonal of the square face of the U-shaped metamaterial. The polarizer is used to transmit polarized light whose polarization direction is perpendicular to the lines of the wire grid and to reflect polarized light whose polarization direction is parallel to the lines of the wire grid.

[0091] U-shaped metamaterials are used to convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light.

[0092] The reflecting unit is perpendicular to the direction of electromagnetic wave propagation, and is used to change the direction of electromagnetic wave propagation without changing the polarization direction of the electromagnetic wave.

[0093] Terahertz electromagnetic waves are incident on a polarizer, forming first linearly polarized light. The first linearly polarized light passes through a U-shaped metamaterial to form first circularly polarized light. The first circularly polarized light is reflected by a reflecting unit to form second circularly polarized light. The second circularly polarized light passes through the U-shaped metamaterial to form second linearly polarized light. The polarization directions of the first and second linearly polarized lights are perpendicular, and the rotation directions of the first and second circularly polarized lights around the propagation direction are opposite. The polarization direction of the second linearly polarized light is parallel to the lines of the grating and cannot pass through the polarizer, so it is reflected by the polarizer.

[0094] In this embodiment, the extension direction of the wire grid is parallel to the diagonal of the square face of the metamaterial periodic unit. For example, after the terahertz electromagnetic wave passes through the polarizer, the polarization direction makes an angle of 45° with the x-axis. The polarized light is decomposed into two linearly polarized beams with equal amplitude and phase in the y and x directions (two adjacent sides of the square face of the metamaterial periodic unit). After passing through the metamaterial, the transmittance in the two directions is close near 1.5 THz. The metamaterial causes the polarized light in the y direction to be 90° ahead, and the linearly polarized light is converted into left-hand circularly polarized light. The left-hand circularly polarized light is converted into right-hand circularly polarized light through the reflection unit. After passing through the metamaterial, the right-hand circularly polarized light forms a linearly polarized wave with a 135° polarization direction. It cannot pass through the polarizer and can only be reflected, thereby achieving the effect of isolating the backlight reflection of the terahertz electromagnetic wave in the optical path.

[0095] It should be noted that after the terahertz electromagnetic wave is reflected by the reflecting unit, the rotation direction of the circularly polarized light remains unchanged, but the propagation direction of the light changes. Therefore, relative to the propagation direction, the rotation direction of the terahertz electromagnetic wave relative to the propagation direction changes after it is reflected by the reflecting unit, either from left-handed to right-handed or from right-handed to left-handed.

[0096] In this embodiment, if the incident angle is not 0°, the second linearly polarized light is reflected out of the optical path. Testing the reflected light can yield the isolation effect of the transmission isolation system. If the incident angle is 45°, the terahertz wave is deflected out of the system in a direction perpendicular to the incident optical path. A receiver perpendicular to the deflected optical path is set up to test the properties of the terahertz wave at a 0° reflection angle. It should be noted that testing the back-transmitted electromagnetic wave with a reflection angle of 0° is of great significance in the study of radar backscattering. If the reflection angle is 0°, the incident and reflected optical paths will coincide, causing the light wave to oscillate within the system. Although the coincidence of optical paths does not affect the application of the transmission isolation system in practical applications, the isolation effect at an incident angle of 0° can be measured through the following embodiment to test the performance of the transmission isolation system:

[0097] Two polarizers and two U-shaped metamaterials are set up, with the two U-shaped metamaterials placed sequentially between the two polarizers;

[0098] The polarizer includes a wire grid, which consists of multiple parallel lines in the same plane. Each line of the wire grid is parallel to the diagonal of the square face of the U-shaped metamaterial periodic unit. The polarizer is used to transmit polarized light whose polarization direction is perpendicular to the lines of the wire grid and to reflect polarized light whose polarization direction is parallel to the lines of the wire grid.

[0099] U-shaped metamaterials are used to convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light.

[0100] Terahertz electromagnetic waves are incident on a polarizer, and after transmission, they form first linearly polarized light. This first linearly polarized light passes through a U-shaped metamaterial to form first circularly polarized light. The first circularly polarized light then passes through another U-shaped metamaterial to form second linearly polarized light. The polarization direction of the second linearly polarized light is perpendicular to that of the first linearly polarized light. The second linearly polarized light is reflected out of the optical path by another polarizer. Using this method, the isolation effect can be measured at any incident angle. Even at 0°, simply by deflecting the angle of the polarizer behind the optical path, the second linearly polarized light can be reflected out of the optical path. The isolation effect can then be determined by measuring the intensity ratio of the reflected light to the incident light. The linear polarization direction of the first linearly polarized light is along the diagonal of the square face of the periodic unit of the U-shaped metamaterial. The isolation degree is obtained by measuring the transmittance after passing through the combination of two sets of polarizers and the metamaterial placed in the same direction.

[0101] The directions of two adjacent sides of the square face of the U-shaped metamaterial are the first direction and the second direction, respectively. The transmittance of the second linearly polarized light in the first direction and the second direction is measured respectively. The insertion loss along the diagonal direction of the square face of the periodic unit of the U-shaped metamaterial is calculated by averaging the two transmittances.

[0102] The formula for determining the polarization state using the Jones matrix is ​​as follows:

[0103]

[0104] Among them, E in G1 and G2 represent the qualitative Jones matrices of the linearly polarized wave LP passing through the polarizer, the metamaterial quarter-wave plate QWP (fast axis along the y-direction), and the reflection component, respectively, where i is the imaginary unit. Due to the change in the propagation direction of the reflected beam, the coordinate system changes; T represents the coordinate transformation matrix between the two coordinate systems. From E... in and E r It can be seen that the reflected linearly polarized wave LP is perpendicular to the polarization direction of the polarizer, and therefore cannot pass through the polarizer. Due to the THz-TDS optical path limitation, the transmittance of two metamaterial QWPs placed in the same direction was measured in the experiment, and the corresponding Jones matrices are as follows:

[0105]

[0106] As can be seen from equations (1) and (2), the linearly polarized wave LP obtained by the two methods is consistent. Based on the above method, the transmittance of the linearly polarized wave LP at different incident angles is measured by using two consecutive metamaterial QWPs, and the blocking efficiency (the ratio of the light power entering the blocking layer to the light power exiting the blocking layer) is calculated.

[0107] In this invention, the wire grid can be fixed on the wire grid fixing ring, the U-shaped metamaterial can be fixed on the metamaterial fixing ring, and the wire grid fixing ring and the metamaterial fixing ring can be combined.

[0108] In some embodiments of the present invention, the diameter of the wire grid is 8 to 12 μm, and the spacing between the wire grid lines is 25 to 35 μm.

[0109] In this embodiment, the polarizer made of the wire grid with the above parameters has a transmittance of 1 in the polarization direction and a transmittance of 0.005 in the direction perpendicular to the polarization direction.

[0110] In some embodiments of the present invention, the wires of the wire grid are made of tungsten wire.

[0111] In this embodiment, the wire grid made of tungsten wire has high contrast.

[0112] like Figure 6 , Figure 7 As shown, in some embodiments of the present invention, the insertion loss, isolation, and blocking bandwidth of the system are adjusted by adjusting the incident angle of the terahertz electromagnetic wave.

[0113] In this embodiment, the insertion loss, isolation, and blocking bandwidth of the transmission isolation system can be finely adjusted by regulating the incident angle of the terahertz electromagnetic wave, with the blocking effect being most pronounced near 1.75 THz. For example, when the incident angle of the terahertz wave is 20 degrees, the isolation can reach over 55 dB at 1.56 THz, and the insertion loss is approximately 1.4 dB.

[0114] It should be noted that, Figure 6 and Figure 7 The angles of incidence in the equation include 0, 10, 20, 30, 40, and 50 degrees.

[0115] This invention also provides an application of any of the above-mentioned terahertz transmission isolation systems to achieve unidirectional and efficient transmission of terahertz waves.

[0116] In this embodiment, the reflection unit in the transmission isolation system can be any optical device. When it is necessary to isolate the terahertz backlight reflection generated by the optical device, the terahertz backlight reflection can be isolated simply by setting a combination of a polarizer and a U-shaped metamaterial in front of the optical device.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a U-shaped metamaterial, characterized in that, include: Polyamic acid is spin-coated onto a substrate to obtain a first preform layer. The first preform layer is then subjected to thermal imidization treatment to obtain a bottom dielectric layer made of polyimide. A U-shaped metal layer is obtained on the upper surface of the bottom dielectric layer using photolithography. Polyamic acid is spin-coated onto the bottom dielectric layer on which the U-shaped metal layer is disposed to obtain a second preform layer. The second preform layer is subjected to the thermal imidization treatment to obtain an intermediate dielectric layer made of polyimide. Another U-shaped metal layer is obtained on the surface of the intermediate dielectric layer away from the bottom dielectric layer using photolithography. Polyamic acid is spin-coated onto the intermediate dielectric layer on which the U-shaped metal layer is disposed to obtain a third prefabricated layer. The third prefabricated layer is subjected to the thermal imidization treatment to obtain a top dielectric layer of polyimide material. A cuboid periodic unit is obtained, including the bottom dielectric layer, the intermediate dielectric layer, the top dielectric layer and the two U-shaped metal layers. The periodic unit includes two square faces. The U-shaped metal layer includes two parallel first metal strips and a second metal strip perpendicular to the first metal strips. The two ends of the second metal strip are respectively connected to the endpoints of the two first metal strips on the same side. The periodic units are periodically arranged along two directions containing the edges of adjacent units that are perpendicular to each other to form a U-shaped metamaterial; The substrate is fixed by positioning holes on the substrate, ensuring that the two U-shaped metal layers are strictly aligned vertically. The side length of the square face of the periodic unit is 40~50 μm; The thickness of the U-shaped metal layer is 180~220nm. The U-shaped metal layer includes two parallel first metal strips and a second metal strip perpendicular to the first metal strips. The width of the first metal strip and the second metal strip is 7~9μm. The length direction of the U-shaped metal layer is the same as the length direction of the first metal strip, and the width direction of the U-shaped metal layer is the same as the length direction of the second metal strip. The length of the U-shaped metal layer is 32~34μm, and the width is 30~32μm.

2. The method according to claim 1, characterized in that, The process of spin-coating polyamic acid onto a square substrate to obtain a first preform layer, and then subjecting the first preform layer to thermal imidization to obtain a bottom dielectric layer made of polyimide, includes: Polyamic acid is spin-coated onto a square substrate at a speed of 700 rpm to obtain a first pre-layer with a thickness of 6-10 μm. The first pre-layer is then subjected to thermal imidization treatment to obtain a bottom dielectric layer with a thickness of 6-10 μm made of polyimide.

3. The method according to claim 1, characterized in that, The process of spin-coating polyamic acid onto the bottom dielectric layer where the U-shaped metal layer is disposed to obtain a second preform layer, and then subjecting the second preform layer to thermal imidization treatment to obtain an intermediate dielectric layer made of polyimide, includes: Polyamic acid is applied to the bottom dielectric layer on which the U-shaped metal layer is disposed at a speed of 1100 rpm to obtain a second prefabricated layer with a thickness of 12~15 μm. The second prefabricated layer is subjected to thermal imidization treatment to obtain an intermediate dielectric layer with a thickness of 12~15 μm and made of polyimide.

4. The method according to claim 1, characterized in that, The process of spin-coating polyamic acid onto the intermediate dielectric layer where the U-shaped metal layer is disposed to obtain a third prefabricated layer, and then subjecting the third prefabricated layer to thermal imidization treatment to obtain a top dielectric layer made of polyimide, includes: Polyamic acid is applied to the intermediate dielectric layer on which the U-shaped metal layer is disposed at a speed of 2600 rpm to obtain a third prefabricated layer with a thickness of 3~7 μm. The third prefabricated layer is subjected to thermal imidization treatment to obtain a top dielectric layer with a thickness of 3~7 μm and made of polyimide.

5. The method according to claim 1, characterized in that, The material used to prepare the U-shaped metal layer includes gold.

6. The method according to claim 1, characterized in that, The thermal imidization treatment includes: Bake at 100~110℃ for 8~12 minutes; Bake at 150~170℃ for 25~35 minutes; Increase the temperature to 280~320℃ at a rate of 3℃ / min and bake for 50~70min.

7. The method according to claim 1, characterized in that, The thermal imidization treatment was carried out under a nitrogen atmosphere.

8. A U-shaped metamaterial, characterized in that, It is prepared by the method according to any one of claims 1-7.

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