A terahertz isolator based on U-shaped metamaterial and its isolation performance test system

Abstract

The present invention relates to the field of isolator technology, and in particular to a terahertz isolator based on a U-shaped metamaterial and an isolation performance testing system. An embodiment of the present invention provides a terahertz isolator based on a U-shaped metamaterial, comprising a U-shaped metamaterial and a polarizer; the U-shaped metamaterial comprises a plurality of periodic units, and the periodic units are periodically arranged along two directions of mutually perpendicular adjacent unit edges to form a metamaterial; the periodic unit is a cuboid comprising two square faces, and comprises a first dielectric layer, a second dielectric layer and a third dielectric layer in sequence along the thickness direction, and the surfaces of the second dielectric layer and the third dielectric layer facing the first dielectric layer are both provided with a U-shaped metal layer; the polarizer is used to transmit polarized light with a polarization direction perpendicular to the lines of the wire grid, and reflect polarized light with a polarization direction parallel to the lines of the wire grid. An embodiment of the present invention provides a terahertz isolator based on a U-shaped metamaterial and a testing system for its terahertz wave isolation performance, which can provide an isolator for isolating terahertz electromagnetic waves.

Description

Technical Field

[0001] The present invention relates to the technical field of isolators, and in particular to an isolator based on a U-shaped metamaterial and an isolation performance testing system. Background Art

[0002] Isolation devices are mainly used for inter-stage isolation, impedance matching, and decoupling between device units to prevent damage to active devices caused by reflected echoes and scattering in the system, reduce the additional noise caused by echoes, and thus improve system stability and reliability.

[0003] In terahertz optical transmission, communication, and radar detection systems, it is often necessary to overcome the interference of back-reflected light. Therefore, there is an urgent need for an isolator for terahertz transmission to ensure the unidirectional and efficient transmission of terahertz waves. Summary of the Invention

[0004] The embodiments of the present invention provide a terahertz isolator based on a U-shaped metamaterial and an isolation performance testing system, which can provide an isolator for isolating reflected terahertz electromagnetic waves.

[0005] In a first aspect, an embodiment of the present invention provides a terahertz isolator based on a U-shaped metamaterial, comprising a U-shaped metamaterial and a polarizer;

[0006] The U-shaped metamaterial comprises a plurality of periodic units, wherein the periodic units are periodically arranged along two directions perpendicular to each other and where edges of adjacent units are located to form the metamaterial;

[0007] The periodic unit is a cuboid with two square faces, and includes a first dielectric layer, a second dielectric layer, and a third dielectric layer in sequence along the thickness direction. The second dielectric layer and the third dielectric layer are both provided with a U-shaped metal layer on the surface facing the first dielectric layer. The U-shaped metal layer includes two mutually 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 on the same side of the two first metal strips.

[0008] The U-shaped metamaterial is used to convert linearly polarized light into circularly polarized light or vice versa;

[0009] The polarizer includes a wire grid, the wire grid includes a plurality of lines parallel to each other in the same plane, each line of the wire grid is parallel to a diagonal line of a periodic unit of the U-shaped metamaterial, and the polarizer is configured to transmit polarized light having a polarization direction perpendicular to the lines of the wire grid and reflect polarized light having a polarization direction parallel to the lines of the wire grid;

[0010] The terahertz electromagnetic wave is incident on the polarizer, and the terahertz electromagnetic wave forms a first linearly polarized light through the polarizer. The first linearly polarized light forms a first circularly polarized light through the U-shaped metamaterial. The first circularly polarized light is reflected by a subsequent optical device to form a second circularly polarized light. The second circularly polarized light forms a second linearly polarized light after passing through the U-shaped metamaterial. The polarization directions of the first linearly polarized light and the second linearly polarized light are perpendicular, and the rotation directions of the first circularly polarized light and the second circularly polarized light around the propagation direction are opposite. The polarization direction of the second linearly polarized light is parallel to the lines of the wire grid and cannot pass through the polarizer. It is reflected by the polarizer to isolate the terahertz electromagnetic wave and prevent the reflected terahertz electromagnetic wave from affecting the incident light source.

[0011] In one possible design, the side length of the square surface of the periodic unit is 40 to 50 μm, the thickness of the first dielectric layer is 3 to 7 μm, the thickness of the second dielectric layer is 12 to 15 μm, the thickness of the third dielectric layer is 6 to 10 μm, and the thickness of the U-shaped metal layer is 180 to 220 nm.

[0012] The width of the first metal strip and the second metal strip is the same as 7 to 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 to 34 μm, and the width is 30 to 32 μm.

[0013] In one possible design, the U-shaped metal layer is made of gold;

[0014] The first dielectric layer, the second dielectric layer and the third dielectric layer are made of polyimide.

[0015] In a second aspect, an embodiment of the present invention further provides an isolation performance testing system, based on the isolator described in any one of the first aspects above, comprising two of the isolators, wherein the U-shaped metamaterials of the two isolators are placed sequentially on the same optical axis;

[0016] The terahertz electromagnetic wave is incident on one of the polarizers and forms the first linearly polarized light after transmission. The first linearly polarized light forms the first circularly polarized light after passing through one of the U-shaped metamaterials. The first circularly polarized light forms the second linearly polarized light after passing through another of the U-shaped metamaterials. 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 the other polarizer.

[0017] The isolation effect can be determined by measuring the intensity ratio of the second linearly polarized light reflected out of the optical path to the incident light. The linear polarization direction of the first linearly polarized light is the diagonal direction of the periodic unit of the U-shaped metamaterial. The isolation degree is obtained by measuring the transmittance of electromagnetic waves passing through the two isolators.

[0018] In one possible design, the directions of two adjacent sides of the square surface of the U-shaped metamaterial are respectively in a first direction and a second direction, and the transmittance of the second linearly polarized light in the first direction and the second direction are tested respectively. The two transmittances are averaged to obtain the insertion loss along the diagonal direction of the periodic unit of the U-shaped metamaterial.

[0019] In a possible design, the diameter of the wire grid wires is 8-12 μm, and the interval between the wire grid wires is 25-35 μm.

[0020] In a possible design, the wires of the wire grid are made of tungsten wire.

[0021] In one possible design, the insertion loss, isolation, and blocking bandwidth of the system are fine-tuned by adjusting the incident angle of the terahertz electromagnetic wave.

[0022] In one possible design, the insertion loss, isolation, and blocking bandwidth of the system are adjusted by adjusting the length and width of the first and second metal strips, and the thickness of the first, second, and third dielectric layers. Compared to the prior art, this invention has at least the following advantages:

[0023] In this embodiment, due to the lack of magneto-optical materials with gyromagnetic or gyroelectric responses in the terahertz band in nature, the present invention provides an artificial U-shaped metamaterial capable of exhibiting gyromagnetic or gyroelectric responses in the terahertz band. The U-shaped metamaterial provided by the present invention is composed of a plurality of periodic units arranged in a periodic manner. The periodic units have a square cross-section and are arranged along two adjacent perpendicular sides of the square, with the side length as the periodicity. The periodic units are composed of a first dielectric layer, a second dielectric layer, and a third dielectric layer stacked sequentially along the thickness direction. The second and third dielectric layers are each provided with a U-shaped metal layer on the surface facing the first dielectric layer, and the two U-shaped metal layers are completely aligned vertically. The metamaterial formed by the periodic units provided with U-shaped metal layers can change the polarization state of a terahertz electromagnetic wave when it passes through. Specifically, the U-shaped metal layer includes two mutually parallel first metal strips and a second metal strip connecting the two first metal strips at the same end point. When a terahertz electromagnetic wave passes through the metamaterial, the terahertz electric field component along the extension direction of the first metal strip increases in phase, thereby changing the polarization state of the terahertz electromagnetic light.

[0024] In this embodiment, the extension direction of the wire grid is parallel to the diagonal of the periodic unit of the metamaterial. The polarized light is decomposed into two beams of linearly polarized light with equal amplitude and phase in the y and x directions (the directions of the two adjacent sides of the square surface of the metamaterial). After passing through the metamaterial, at around 1.5 THz, the transmittance in the two directions is close. The metamaterial advances the polarized light in the y direction by 90°, and the linearly polarized light is converted into left-handed circularly polarized light. The left-handed circularly polarized light is converted into right-handed circularly polarized light through the reflection unit. After passing through the metamaterial, the right-handed circularly polarized light forms linearly polarized light with a polarization direction of 135°, which is reflected out of the optical path by the polarizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a schematic diagram of the application structure of a terahertz isolator provided by an embodiment of the present invention;

[0027] Figure 2 This is a structural diagram of an isolation performance testing system provided by an embodiment of the present invention;

[0028] Figure 3 1 is a schematic structural diagram of an isolator provided by an embodiment of the present invention;

[0029] Figure 4 1 is a schematic structural diagram of a polarizer provided by an embodiment of the present invention;

[0030] Figure 5 is a schematic side cross-sectional structure diagram of a periodic unit provided by an embodiment of the present invention;

[0031] Figure 6 1 is a schematic diagram of a top view of a periodic unit provided by an embodiment of the present invention;

[0032] Figure 7 is an insertion loss diagram of an isolator provided by an embodiment of the present invention;

[0033] Figure 8 This is an isolation diagram of an isolator provided by an embodiment of the present invention.

[0034] In the picture:

[0035] 1-wire grid fixing ring;

[0036] 2-wire grid;

[0037] 3-U-shaped metamaterial;

[0038] 4-metamaterial fixing ring;

[0039] 5-first dielectric layer;

[0040] 6- second dielectric layer;

[0041] 7- third dielectric layer;

[0042] 8-U-shaped metal layer;

[0043] 9- first metal strip;

[0044] 10- second metal strip;

[0045] 100-Reflection unit. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] In the description of the embodiments of the present invention, unless otherwise expressly specified or limited, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance; unless otherwise specified or explained, the term "plurality" refers to two or more; the terms "connected" and "fixed" should be understood in a broad sense. For example, "connected" can mean 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. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] In the description of this specification, it should be understood that the directional terms such as "upper" and "lower" described in the embodiments of the present invention are described from the perspectives shown in the accompanying drawings and should not be understood as limiting the embodiments of the present invention. In addition, in the context, it should be understood that when it is mentioned that an element is connected "upper" or "lower" of another element, it can not only be directly connected "upper" or "lower" of the other element, but also indirectly connected "upper" or "lower" of the other element through an intermediate element.

[0049] like Figure 1 、 3 , 4, 5, and 6, an embodiment of the present invention provides an isolator based on a U-shaped metamaterial, including a U-shaped metamaterial and a polarizer;

[0050] The U-shaped metamaterial comprises a plurality of periodic units, which are periodically arranged along two directions perpendicular to each other and where the edges of adjacent units are located to form the metamaterial;

[0051] The periodic unit is a cuboid with two square faces, which includes a first dielectric layer, a second dielectric layer, and a third dielectric layer in sequence along the thickness direction. The second dielectric layer and the third dielectric layer are both provided with a U-shaped metal layer on the surface facing the first dielectric layer. The U-shaped metal layer includes two mutually 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 on the same side of the two first metal strips.

[0052] The U-shaped metamaterial is used to convert linearly polarized light into circularly polarized light or vice versa;

[0053] The polarizer includes a wire grid, which includes multiple lines parallel to each other in the same plane, each line of the wire grid is parallel to the diagonal line of the periodic unit of the U-shaped metamaterial, and the polarizer is used to transmit polarized light with a polarization direction perpendicular to the lines of the wire grid and reflect polarized light with a polarization direction parallel to the lines of the wire grid;

[0054] The terahertz electromagnetic wave is incident on the polarizer, and the terahertz electromagnetic wave forms a first linearly polarized light through the polarizer. The first linearly polarized light forms a first circularly polarized light through the U-shaped metamaterial. The first circularly polarized light is reflected by the subsequent optical device to form a second circularly polarized light. The second circularly polarized light forms a second linearly polarized light after passing through the U-shaped metamaterial. The polarization directions of the first linearly polarized light and the second linearly polarized light are perpendicular, and the rotation directions of the first circularly polarized light and the second circularly polarized light around the propagation direction are opposite. The polarization direction of the second linearly polarized light is parallel to the lines of the wire grid and cannot pass through the polarizer. It is reflected by the polarizer to isolate the terahertz electromagnetic wave and prevent the reflected terahertz electromagnetic wave from affecting the incident light source.

[0055] In this embodiment, due to the lack of magneto-optical materials with gyromagnetic or gyroelectric responses in the terahertz band in nature, the present invention provides an artificial U-shaped metamaterial capable of exhibiting gyromagnetic or gyroelectric responses in the terahertz band. The U-shaped metamaterial provided by the present invention is composed of a plurality of periodic units arranged in a periodic manner. The periodic units have a square cross-section and are arranged along two adjacent perpendicular sides of the square, with the side length as the periodicity. The periodic units are composed of a first dielectric layer, a second dielectric layer, and a third dielectric layer stacked sequentially along the thickness direction. The second and third dielectric layers are each provided with a U-shaped metal layer on the surface facing the first dielectric layer, and the two U-shaped metal layers are completely aligned vertically. The metamaterial formed by the periodic units provided with U-shaped metal layers can change the polarization state of a terahertz electromagnetic wave when it passes through. Specifically, the U-shaped metal layer includes two mutually parallel first metal strips and a second metal strip connecting the two first metal strips at the same end point. When a terahertz electromagnetic wave passes through the metamaterial, the terahertz electric field component along the extension direction of the first metal strip increases in phase, thereby changing the polarization state of the terahertz electromagnetic light.

[0056] In this embodiment, the extension direction of the wire grid is parallel to the diagonal line of the periodic unit of the metamaterial, for example, Figure 1 At the position shown, after the terahertz electromagnetic wave passes through the polarizer, the polarization direction includes an angle of 45° with the x-axis. The polarized light is decomposed into two beams of linearly polarized light with equal amplitude and phase in the y and x directions (the directions of the two adjacent sides of the square surface of the metamaterial). After passing through the metamaterial, near 1.5 THz, the transmittance in the two directions is close. The metamaterial advances the polarized light in the y direction by 90°, and the linearly polarized light is converted into left-handed circularly polarized light. The left-handed circularly polarized light is converted into right-handed circularly polarized light through the reflection unit. After passing through the metamaterial, the right-handed circularly polarized light forms a linearly polarized wave with a polarization direction of 135°, which is reflected out of the optical path by the polarizer.

[0057] It should be noted that after the reflection unit reflects the terahertz electromagnetic wave, the rotation direction of the circularly polarized light remains unchanged, but the propagation direction of the light changes. Therefore, relative to the propagation direction, after the terahertz electromagnetic wave is reflected by the reflection unit, the rotation direction relative to the propagation direction changes, and the relative propagation direction changes from left-handed to right-handed or from right-handed to left-handed.

[0058] In this embodiment, if the incident angle is not 0°, the second linearly polarized light is reflected out of the optical path. Testing the light reflected out of the optical path can determine the isolation effect of the 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 to test the properties of the terahertz wave at a 0° reflection angle. It should be noted that testing the backward-transmitting electromagnetic wave with a reflection angle of 0° is of great significance in studying radar backscattering. If the reflection angle is 0°, the incident optical path and the reflected optical path will overlap, causing the light wave to oscillate within the system. In practical applications, the overlap of the optical paths will not affect the application of the optical system and the isolation of the terahertz electromagnetic wave.

[0059] In some embodiments of the present invention, the side length of the square surface of the periodic unit is 40-50 μm, the thickness of the first dielectric layer is 3-7 μm, the thickness of the second dielectric layer is 12-15 μm, the thickness of the third dielectric layer is 6-10 μm, and the thickness of the U-shaped metal layer is 180-220 nm;

[0060] The width of the first metal strip and the second metal strip is 7 to 9 μm. The length direction of the U-shaped metal layer is the same as that of the first metal strip. The width direction of the U-shaped metal layer is the same as that of the second metal strip. The length of the U-shaped metal layer is 32 to 34 μm and the width is 30 to 32 μm.

[0061] In this embodiment, the side length of the square surface of the periodic unit is 40-50 μm, the thickness of the first dielectric layer is 3-7 μm, the thickness of the second dielectric layer is 12-15 μm, the thickness of the third dielectric layer is 6-10 μm, and the thickness of the U-shaped metal layer is 180-220 nm. The parameters of the periodic unit can affect the performance of the metamaterial. Within the above range, the metamaterial is excellent in changing the polarization state of terahertz waves.

[0062] In this embodiment, the widths of the first and second metal strips are both 7 to 9 μm. The length of the U-shaped metal layer is aligned with the length of the first metal strip, and the width of the U-shaped metal layer is aligned with the length of the second metal strip. The length of the U-shaped metal layer is 32 to 34 μm, and the width is 30 to 32 μm. The parameters of the U-shaped metal layer can affect the performance of the metamaterial. Within the above range, the metamaterial exhibits excellent performance in altering the polarization state of terahertz waves.

[0063] In some embodiments of the present invention, the material for preparing the U-shaped metal layer includes gold;

[0064] The materials used to prepare the first dielectric layer, the second dielectric layer and the third dielectric layer include polyimide.

[0065] In this embodiment, gold has excellent and stable physical and chemical properties, is an excellent conductor, and has excellent machinability. Selecting gold as the material for preparing the U-shaped metal layer can further enhance the performance of the metamaterial and facilitate its processing and fabrication.

[0066] In this embodiment, the first dielectric layer, the second dielectric layer, and the third dielectric layer are made of polyimide. Polyimide is flexible, insulating, has mature technology, is easy to process, and is also a good medium for propagating terahertz electromagnetic waves.

[0067] like Figure 2 、 3 , 4, 5 and 6, an embodiment of the present invention further provides an isolation performance testing system, based on any one of the above isolators, comprising two of the isolators, the U-shaped metamaterials of the two isolators being placed sequentially on the same optical axis;

[0068] The terahertz electromagnetic wave is incident on one of the polarizers and forms the first linearly polarized light after transmission. The first linearly polarized light passes through one of the U-shaped metamaterials to form the first circularly polarized light. The first circularly polarized light passes through another U-shaped metamaterial parallel to the front one to form the second linearly polarized light. The polarization direction of the second linear polarized light is perpendicular to that of the first linear polarized light. The second linear polarized light is reflected out of the optical path by the other polarizer.

[0069] The above method can measure the isolation effect at any incident angle. Even if the incident angle is 0°, the second linearly polarized light can be reflected out of the light path by simply deflecting the angle of the polarizer behind the light path. Then, the second linearly polarized light reflected out of the light path can be tested. The isolation effect can be known by measuring the light intensity ratio of the reflected light out of the light path to the incident light. The linear polarization direction of the first linearly polarized light is the diagonal direction of the periodic unit of the U-shaped metamaterial. The isolation degree is obtained by testing the transmittance of the combination of the two sets of polarizers and the metamaterial placed in the same direction.

[0070] The directions of two adjacent sides of the square surface of the U-shaped metamaterial are respectively in the first direction and the second direction. The transmittance of the second linearly polarized light in the first direction and the second direction is tested respectively, and the two transmittances are averaged to obtain the insertion loss along the diagonal direction of the periodic unit of the U-shaped metamaterial.

[0071] The formula for determining the polarization state using the Jones matrix is ​​as follows:

[0072]

[0073] Among them, E inG1, 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 reflected component, respectively. i is an imaginary unit. Due to the change in the propagation direction of the reflected light beam, the coordinate system has changed. T represents the coordinate transformation matrix between the two coordinate systems. E in and E r It can be seen that the reflected linearly polarized wave LP wave is perpendicular to the polarization direction of the polarizer, so it cannot pass through the polarizer. Due to the limitation of the THz-TDS optical path, the transmittance of two metamaterial QWPs placed in the same direction was measured in the experiment, such as Figure 2 As shown, it is equivalent to Figure 1 The blocking reflection process in , the corresponding Jones matrix is ​​as follows:

[0074]

[0075] From equations (1) and (2), it can be seen that 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 through two consecutive metamaterial QWPs, and the blocking efficiency (the ratio of the optical power entering the blocking layer to the optical power exiting the blocking layer) is calculated.

[0076] In some embodiments of the present invention, the diameter of the wire grid is 8-12 μm, and the spacing between the wire grid wires is 25-35 μm.

[0077] In this embodiment, the transmittance of the polarizer made of the wire grid with the above parameters is 1 in the polarization direction and 0.005 in the direction perpendicular to the polarization direction.

[0078] In some embodiments of the present invention, the wires of the wire grid are made of tungsten wire.

[0079] In this embodiment, the wire grid made of tungsten wires has high contrast.

[0080] like Figure 7 、 8 As shown, in some embodiments of the present invention, the insertion loss, isolation and blocking bandwidth of the system are fine-tuned by adjusting the incident angle of the terahertz electromagnetic wave.

[0081] In this embodiment, the insertion loss, isolation, and blocking bandwidth of the transmission isolation system can be fine-tuned by adjusting the incident angle of the terahertz electromagnetic wave. The blocking effect is most pronounced near 1.75 THz. For example, when the incident angle of the terahertz wave is 20 degrees, the isolation reaches a maximum of over 55 dB at 1.56 THz, with an insertion loss of approximately 1.4 dB.

[0082] It should be noted that Figure 7 and Figure 8The degrees of the incident angle include 0, 10, 20, 30, 40 and 50.

[0083] 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, it is only necessary to set a combination of a polarizer and a U-shaped metamaterial in front of the optical device to isolate the terahertz backlight reflection.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A terahertz isolator based on U-shaped metamaterial, characterized in that: Includes U-shaped metamaterial and polarizer; The U-shaped metamaterial comprises a plurality of periodic units, wherein the periodic units are periodically arranged along two directions perpendicular to each other and where edges of adjacent units are located to form the metamaterial; The periodic unit is a cuboid with two square faces, and includes a first dielectric layer, a second dielectric layer, and a third dielectric layer in sequence along the thickness direction. The second dielectric layer and the third dielectric layer are both provided with a U-shaped metal layer on the surface facing the first dielectric layer. The two U-shaped metal layers are aligned vertically along the thickness direction. The U-shaped metal layer includes two mutually 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 on the same side of the two first metal strips. The U-shaped metamaterial is used to convert linearly polarized light into circularly polarized light or vice versa; The polarizer includes a wire grid, the wire grid includes a plurality of lines parallel to each other in the same plane, each line of the wire grid is parallel to the diagonal line of the periodic unit of the U-shaped metamaterial, and the polarizer is used to transmit polarized light with a polarization direction perpendicular to the lines of the wire grid and reflect polarized light with a polarization direction parallel to the lines of the wire grid; The terahertz electromagnetic wave is incident on the polarizer, and the terahertz electromagnetic wave forms a first linearly polarized light through the polarizer. The first linearly polarized light forms a first circularly polarized light through the U-shaped metamaterial. The first circularly polarized light is reflected by a subsequent optical device to form a second circularly polarized light. The second circularly polarized light forms a second linearly polarized light after passing through the U-shaped metamaterial. The polarization directions of the first linearly polarized light and the second linearly polarized light are perpendicular, and the rotation directions of the first circularly polarized light and the second circularly polarized light around the propagation direction are opposite. The polarization direction of the second linearly polarized light is parallel to the lines of the wire grid and cannot pass through the polarizer. It is reflected by the polarizer to isolate the terahertz electromagnetic wave and prevent the reflected terahertz electromagnetic wave from affecting the incident light source.

2. The isolator according to claim 1, characterized in that The side length of the square surface of the periodic unit is 40-50 μm, the thickness of the first dielectric layer is 3-7 μm, the thickness of the second dielectric layer is 12-15 μm, the thickness of the third dielectric layer is 6-10 μm, and the thickness of the U-shaped metal layer is 180-220 nm; The widths of the first metal strip and the second metal strip are both 7~9μm, 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 32~34μm, and the width is 30~32μm.

3. The isolator according to claim 2, characterized in that The preparation material of the U-shaped metal layer includes gold; The first dielectric layer, the second dielectric layer and the third dielectric layer are made of polyimide.

4. An isolation performance testing system, characterized in that: The isolator according to any one of claims 1 to 3, comprising two isolators, wherein the U-shaped metamaterials of the two isolators are placed sequentially on the same optical axis; The terahertz electromagnetic wave is incident on one of the polarizers and forms the first linearly polarized light after transmission. The first linearly polarized light forms the first circularly polarized light after passing through one of the U-shaped metamaterials. The first circularly polarized light forms the second linearly polarized light after passing through another of the U-shaped metamaterials. 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 the other polarizer. The isolation effect can be determined by measuring the intensity ratio of the second linearly polarized light reflected out of the optical path to the incident light. The linear polarization direction of the first linearly polarized light is the diagonal direction of the periodic unit of the U-shaped metamaterial. The isolation degree is obtained by measuring the transmittance of electromagnetic waves passing through the two isolators.

5. The system according to claim 4, characterized in that The directions of two adjacent sides of the square surface of the U-shaped metamaterial are respectively a first direction and a second direction, and the transmittance of the second linearly polarized light in the first direction and the second direction are tested respectively. The two transmittances are averaged to obtain the insertion loss along the diagonal direction of the periodic unit of the U-shaped metamaterial.

6. The system according to claim 4, characterized in that The diameter of the wire grid is 8-12 μm, and the interval between the wire grid wires is 25-35 μm.

7. The system according to claim 4, wherein: The wires of the wire grid are made of tungsten wire.

8. The system according to claim 4, wherein: The insertion loss, isolation and blocking bandwidth of the system can be fine-tuned by adjusting the incident angle of the terahertz electromagnetic wave.

9. The system according to claim 4, wherein: The insertion loss, isolation and blocking bandwidth of the system can be adjusted by adjusting the length and width of the first metal strip and the second metal strip, and the thickness of the first dielectric layer, the second dielectric layer and the third dielectric layer.

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