A terahertz isolator and isolation performance test system based on closed-loop metamaterial

Abstract

The present invention relates to the field of isolator technology, and in particular to a terahertz isolator based on a closed-loop metamaterial and an isolation performance testing system. An embodiment of the present invention provides a terahertz isolator based on a closed-loop metamaterial, comprising a closed-loop metamaterial and a polarizer; the closed-loop metamaterial comprises a plurality of periodic units, and the periodic units are periodically arranged in two directions where the edges of adjacent units are perpendicular to each other 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 closed-loop 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 closed-loop 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 a terahertz isolator based on closed-loop metamaterials 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 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 closed-loop 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 an isolator based on a closed-loop metamaterial, comprising a closed-loop metamaterial and a polarizer;

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

[0007] The periodic unit is a cuboid including two square faces, and includes a first dielectric layer, a second dielectric layer and a third dielectric layer in sequence along the thickness direction, and the second dielectric layer and the third dielectric layer are both provided with a closed-loop metal layer on the surface facing the first dielectric layer, and the closed-loop metal layer includes a rectangular metal ring and two T-shaped metal sheets arranged inside the metal ring, and the T-shaped metal sheet includes a first metal arm and a second metal arm perpendicular to each other, and one end of the second metal arm is connected to the midpoint of the first metal arm, and the other end is connected to the midpoint of the long arm of the metal ring;

[0008] Closed-loop metamaterials are used to convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light;

[0009] The polarizer comprises a wire grid, the wire grid comprises 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 closed-loop metamaterial, and the polarizer is used 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] A terahertz electromagnetic wave is incident on the polarizer, the terahertz electromagnetic wave forms a first linear polarized light through the polarizer, the first linear polarized light forms a first circular polarized light through the closed-loop metamaterial, the first circular polarized light forms a second circular polarized light after being reflected by a subsequent optical device, the second circular polarized light forms a second linear polarized light after passing through the closed-loop metamaterial, the polarization directions of the first linear polarized light and the second linear polarized light are perpendicular, the rotation directions of the first circular polarized light and the second circular polarized light around the propagation direction are opposite, the polarization direction of the second linear polarized light is parallel to the lines of the wire grid, and cannot pass through the polarizer, and is reflected by the polarizer to isolate the terahertz electromagnetic wave, thereby preventing the reflected terahertz electromagnetic wave from affecting the incident light source.

[0011] In a possible design, 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 10-15 μm, the thickness of the third dielectric layer is 6-10 μm, and the thickness of the closed-loop metal layer is 180-220 nm;

[0012] The widths of the first metal arm, the second metal arm and the metal ring are all 2 to 4 μm, the length of the first metal arm is 8 to 12 μm, the distance between the two first metal arms is 1 to 3 μm, the length of the metal ring is 29 to 31 μm, and the width of the metal ring is 22 to 24 μm.

[0013] In a possible design, the closed-loop metal layer is made of a material including 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 terahertz isolator described in any one of the first aspects, comprising two of the isolators, wherein the closed-loop 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 linear polarized light after transmission. The first linear polarized light passes through one of the closed-loop metamaterials to form the first circular polarized light. The first circular polarized light passes through another closed-loop metamaterial to form the second linear polarized light. The polarization directions of the second linear polarized light and the first linear polarized light are perpendicular. The second linear polarized light is reflected out of the optical path by another polarizer.

[0017] The isolation effect can be known by measuring the light 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 closed-loop metamaterial. The isolation degree is obtained by testing the transmittance of electromagnetic waves passing through the two isolators.

[0018] In a possible design, the directions of two adjacent sides of the square surface of the closed-loop 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, and the two transmittances are averaged to obtain the insertion loss along the diagonal direction of the periodic unit of the closed-loop metamaterial.

[0019] In a possible design, the diameter of the wires of the wire grid is 8-12 μm, and the interval between the wires of the wire grid 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 a possible design, the insertion loss, isolation and blocking bandwidth of the system are adjusted by adjusting the length and width of the metal ring, the length of the first metal arm and the second metal arm, and the thickness of the first dielectric layer, the second dielectric layer and the third dielectric layer.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] In this embodiment, since nature itself lacks magneto-optical materials with gyromagnetic or gyroelectric responses in the terahertz band, the present invention provides an artificial closed-loop metamaterial that can have gyromagnetic or gyroelectric responses in the terahertz band. The closed-loop metamaterial provided by the present invention is composed of a plurality of periodic units arranged periodically, the cross-section of the periodic unit is a square, and the periodic units are arranged along two adjacent sides perpendicular to the square with the side length as a period to form a metamaterial. The periodic unit is composed of a first dielectric layer, a second dielectric layer, and a third dielectric layer stacked in sequence along the thickness direction, and the second dielectric layer and the third dielectric layer are both provided with closed-loop metal layers on the surfaces facing the first dielectric layer, and the two closed-loop metal layers are completely aligned up and down. The metamaterial formed by the periodic unit provided with a closed-loop metal layer can change the polarization state of the terahertz electromagnetic wave when the terahertz electromagnetic wave passes through. Specifically, the closed-loop metal layer includes a rectangular metal ring and two T-shaped metal sheets arranged inside the metal ring. The T-shaped metal sheet includes a first metal arm and a second metal arm that are perpendicular to each other. One end of the second metal arm is connected to the midpoint of the first metal arm, and the other end is connected to the midpoint of the long arm of the metal ring. When the terahertz electromagnetic wave passes through the metamaterial, the terahertz electric field component along the extension direction of the second metal arm increases the phase, thereby changing the polarization state of the terahertz electromagnetic wave.

[0025] In this embodiment, the extension direction of the wire grid is parallel to the diagonal of the periodic unit of the metamaterial, and 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 two adjacent sides of the square surface of the metamaterial). After passing through the metamaterial, near 1.5 THz, the transmittances in the two directions are 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. The right-handed circularly polarized light forms a linearly polarized light with a polarization direction of 135° after passing through the metamaterial, and is reflected out of the light path by the polarizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0027] Figure 1 is a schematic diagram of an application structure of a terahertz isolator provided by an embodiment of the present invention;

[0028] Figure 2 It is a structural schematic diagram of an isolation performance testing system provided by an embodiment of the present invention;

[0029] Figure 3 is a schematic structural diagram of an isolator provided by an embodiment of the present invention;

[0030] Figure 4 is a schematic structural diagram of a polarizer provided by an embodiment of the present invention;

[0031] Figure 5 is a schematic diagram of a side cross-sectional structure of a periodic unit provided by an embodiment of the present invention;

[0032] Figure 6 is a schematic diagram of a top view structure of a periodic unit provided by an embodiment of the present invention;

[0033] Figure 7 is an insertion loss diagram of an isolator provided by an embodiment of the present invention;

[0034] Figure 8 This is an isolation diagram of an isolator provided by an embodiment of the present invention.

[0035] In the figure:

[0036] 1-Wire grid fixing ring;

[0037] 2-wire grid;

[0038] 3- Closed-loop metamaterials;

[0039] 4-Metamaterial fixing ring;

[0040] 5-first dielectric layer;

[0041] 6- second dielectric layer;

[0042] 7- third dielectric layer;

[0043] 8- Closed loop metal layer;

[0044] 9- first metal strip;

[0045] 10- second metal strip;

[0046] 100-Reflection unit. DETAILED DESCRIPTION

[0047] 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, rather than all the embodiments. Based on the embodiments in 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.

[0048] In the description of the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; unless otherwise specified or explained, the term "multiple" refers to two or more; the terms "connected" and "fixed" should be understood in a broad sense, for example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] In the description of this specification, it should be understood that the directional words such as "upper" and "lower" described in the embodiments of the present invention are described at the angles shown in the drawings and should not be understood as limiting the embodiments of the present invention. In addition, in the context, it should also be understood that when it is mentioned that an element is connected to another element "upper" or "lower", it can not only be directly connected to another element "upper" or "lower", but also indirectly connected to another element "upper" or "lower" through an intermediate element.

[0050] like Figure 1 , 3 , 4, 5, and 6, an embodiment of the present invention provides a terahertz isolator based on a closed-loop metamaterial, including a closed-loop metamaterial and a polarizer;

[0051] The closed-loop metamaterial includes a plurality of periodic units, and the periodic units are periodically arranged along two directions perpendicular to each other where the edges of adjacent units are located to form the metamaterial;

[0052] The periodic unit is a cuboid including 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 surfaces of the second dielectric layer and the third dielectric layer facing the first dielectric layer are both provided with a closed-loop metal layer, and the closed-loop metal layer includes a rectangular metal ring and two T-shaped metal sheets arranged inside the metal ring. The T-shaped metal sheet includes a first metal arm and a second metal arm perpendicular to each other, and one end of the second metal arm is connected to the midpoint of the first metal arm, and the other end is connected to the midpoint of the long arm of the metal ring;

[0053] Closed-loop metamaterials are used to convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light;

[0054] 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 closed-loop metamaterial, and the polarizer is used 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;

[0055] The terahertz electromagnetic wave is incident on a polarizer, and the terahertz electromagnetic wave forms a first linear polarized light through the polarizer, and the first linear polarized light forms a first circular polarized light through the closed-loop metamaterial, and the first circular polarized light forms a second circular polarized light after being reflected by a subsequent optical device, and the second circular polarized light forms a second linear polarized light after passing through the closed-loop metamaterial, and the polarization directions of the first linear polarized light and the second linear polarized light are perpendicular, and the rotation directions of the first circular polarized light and the second circular polarized light around the propagation direction are opposite, and the polarization direction of the second linear polarized light is parallel to the lines of the wire grid, and cannot pass through the polarizer, and is reflected by the polarizer to isolate the terahertz electromagnetic wave and prevent the reflected terahertz electromagnetic wave from affecting the incident light source.

[0056] In this embodiment, since nature itself lacks magneto-optical materials with gyromagnetic or gyroelectric responses in the terahertz band, the present invention provides an artificial closed-loop metamaterial that can have gyromagnetic or gyroelectric responses in the terahertz band. The closed-loop metamaterial provided by the present invention is composed of a plurality of periodic units arranged periodically, the cross-section of the periodic unit is a square, and the periodic units are arranged along two adjacent sides perpendicular to the square with the side length as a period to form a metamaterial. The periodic unit is composed of a first dielectric layer, a second dielectric layer, and a third dielectric layer stacked in sequence along the thickness direction, and the second dielectric layer and the third dielectric layer are both provided with closed-loop metal layers on the surfaces facing the first dielectric layer, and the two closed-loop metal layers are completely aligned up and down. The metamaterial formed by the periodic unit provided with a closed-loop metal layer can change the polarization state of the terahertz electromagnetic wave when the terahertz electromagnetic wave passes through. Specifically, the closed-loop metal layer includes a rectangular metal ring and two T-shaped metal sheets arranged inside the metal ring. The T-shaped metal sheet includes a first metal arm and a second metal arm that are perpendicular to each other. One end of the second metal arm is connected to the midpoint of the first metal arm, and the other end is connected to the midpoint of the long arm of the metal ring. When the terahertz electromagnetic wave passes through the metamaterial, the terahertz electric field component along the extension direction of the second metal arm increases the phase, thereby changing the polarization state of the terahertz electromagnetic wave.

[0057] 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 angle between the polarization direction and the x-axis is 45°, and the polarized light is decomposed into two linearly polarized lights with equal amplitudes and phases 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 transmittances in the two directions are 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 polarized at 135°, which is reflected out of the light path by the polarizer.

[0058] 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.

[0059] In this embodiment, if the incident angle is not 0°, the second linear polarized light is reflected out of the optical path, and the isolation effect of the isolation system can be obtained by testing the light reflected out of the optical path. If the incident angle is 45°, the terahertz wave is just 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 transmission 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 in 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.

[0060] 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 10-15 μm, the thickness of the third dielectric layer is 6-10 μm, and the thickness of the closed-loop metal layer is 180-220 nm;

[0061] The widths of the first metal arm, the second metal arm and the metal ring are all 2-4 μm, the length of the first metal arm is 8-12 μm, the distance between the two first metal arms is 1-3 μm, the length of the metal ring is 29-31 μm, and the width of the metal ring is 22-24 μm.

[0062] 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 10-15 μm, the thickness of the third dielectric layer is 6-10 μm, and the thickness of the closed-loop metal layer is 180-220 nm. The parameters of the periodic unit can affect the performance of the metamaterial. When the parameters are within the above range, the metamaterial has an excellent effect of changing the polarization state of the terahertz wave.

[0063] In this embodiment, the widths of the first metal arm, the second metal arm and the metal ring are all 2 to 4 μm, the length of the first metal arm is 8 to 12 μm, the distance between the two first metal arms is 1 to 3 μm, the length of the metal ring is 29 to 31 μm, and the width of the metal ring is 22 to 24 μm. Within the above parameters, the metamaterial has an excellent effect in changing the polarization state of the terahertz wave.

[0064] In some embodiments of the present invention, the closed-loop metal layer is prepared from a material including gold;

[0065] The materials used to make the first dielectric layer, the second dielectric layer and the third dielectric layer include polyimide.

[0066] In this embodiment, gold has excellent and stable physical and chemical properties, is an excellent conductor, and has excellent processability. Selecting gold as the preparation material of the closed-loop metal layer can further improve the performance of the metamaterial and facilitate processing to obtain the metamaterial.

[0067] In this embodiment, the preparation material of the first dielectric layer, the second dielectric layer and the third dielectric layer includes polyimide. Polyimide is flexible, insulating, has mature technology, is easy to process, and is also a good medium for propagating terahertz electromagnetic waves.

[0068] like Figure 2 , 3 , 4, 5 and 6, an embodiment of the present invention further provides an isolation performance test system, based on the isolator described in any one of the above, comprising two of the isolators, the closed-loop metamaterials of the two isolators being placed sequentially on the same optical axis;

[0069] The terahertz electromagnetic wave is incident on one of the polarizers and forms the first linear polarized light after transmission. The first linear polarized light passes through one of the closed-loop metamaterials to form the first circularly polarized light. The first circularly polarized light passes through another closed-loop metamaterial parallel to the front one to form the second linear 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 light path by another polarizer.

[0070] By using the above method, the isolation effect under any incident angle can be measured. Even if the incident angle is 0°, the second linear polarized light can be reflected out of the light path by simply deflecting the angle of the polarizer behind the light path, and then the second linear 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 linear polarized light is the diagonal direction of the periodic unit of the closed-loop metamaterial. The isolation degree is obtained by testing the transmittance after passing through the combination of two sets of polarizers and the metamaterial placed in the same direction.

[0071] The directions of two adjacent sides of the square surface of the closed-loop metamaterial are respectively the first direction and the second direction, the transmittance of the second linearly polarized light in the first direction and the second direction are tested respectively, and the two transmittances are averaged to obtain the insertion loss along the diagonal direction of the periodic unit of the closed-loop metamaterial.

[0072] The formula for determining the polarization state using the Jones matrix is ​​as follows:

[0073]

[0074] Among them, E in G1, G2 represent the qualitative Jones matrices of the linear polarization wave LP passing through the polarizer, the metamaterial quarter wave plate QWP (fast axis along the y direction) and the reflected component, respectively, and i is an imaginary unit. Due to the change in the propagation direction of the reflected light beam, the coordinate system has changed, and T represents the coordinate transformation matrix between the two coordinate systems. 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:

[0075]

[0076] It can be seen from equations (1) and (2) that the linearly polarized wave LP waves obtained by the two methods are 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 emitted from the blocking layer) is calculated.

[0077] In some embodiments of the present invention, the diameter of the wires of the wire grid is 8-12 μm, and the interval between the wires of the wire grid is 25-35 μm.

[0078] In this embodiment, the transmittance of the polarizer made of the wire grid with the above parameters is 1 in the polarization direction, and the transmittance in the direction perpendicular to the polarization direction is 0.005.

[0079] In some embodiments of the present invention, the wires of the wire grid are made of tungsten wire.

[0080] In this embodiment, the wire grid made of tungsten wire has a high contrast.

[0081] 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.

[0082] In this embodiment, the insertion loss, isolation and blocking bandwidth of the isolation system can be fine-tuned by adjusting the incident angle of the terahertz electromagnetic wave, and the blocking effect is most obvious near 1.6 THz.

[0083] 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 embodiments of the present invention.

Claims

1. A terahertz isolator based on closed-loop metamaterial, characterized in that: Includes closed-loop metamaterials and polarizers; The closed-loop metamaterial comprises a plurality of periodic units, and the periodic units are periodically arranged along two directions perpendicular to each other and where the edges of adjacent units are located to form the metamaterial; The periodic unit is a cuboid including two square faces, and includes a first dielectric layer, a second dielectric layer and a third dielectric layer in sequence along the thickness direction, and the second dielectric layer and the third dielectric layer are both provided with a closed-loop metal layer on the surface facing the first dielectric layer, and the closed-loop metal layer includes a rectangular metal ring and two T-shaped metal sheets arranged inside the metal ring, and the T-shaped metal sheet includes a first metal arm and a second metal arm perpendicular to each other, and one end of the second metal arm is connected to the midpoint of the first metal arm, and the other end is connected to the midpoint of the long arm of the metal ring; Closed-loop metamaterials are used to convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light; The polarizer comprises a wire grid, the wire grid comprises 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 the periodic unit of the closed-loop metamaterial, and the polarizer is used 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; A terahertz electromagnetic wave is incident on the polarizer, the terahertz electromagnetic wave forms a first linear polarized light through the polarizer, the first linear polarized light forms a first circular polarized light through the closed-loop metamaterial, the first circular polarized light forms a second circular polarized light after being reflected by a subsequent optical device, the second circular polarized light forms a second linear polarized light after passing through the closed-loop metamaterial, the polarization directions of the first linear polarized light and the second linear polarized light are perpendicular, the rotation directions of the first circular polarized light and the second circular polarized light around the propagation direction are opposite, the polarization direction of the second linear polarized light is parallel to the lines of the wire grid, and cannot pass through the polarizer, and is reflected by the polarizer to isolate the terahertz electromagnetic wave, thereby preventing 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 10-15 μm, the thickness of the third dielectric layer is 6-10 μm, and the thickness of the closed-loop metal layer is 180-220 nm; The widths of the first metal arm, the second metal arm and the metal ring are all 2 to 4 μm, the length of the first metal arm is 8 to 12 μm, the distance between the two first metal arms is 1 to 3 μm, the length of the metal ring is 29 to 31 μm, and the width of the metal ring is 22 to 24 μm.

3. The isolator according to claim 2, characterized in that The preparation material of the closed-loop 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 of the isolators, wherein the closed-loop 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 linear polarized light after transmission. The first linear polarized light passes through one of the closed-loop metamaterials to form the first circular polarized light. The first circular polarized light passes through another closed-loop metamaterial to form the second linear polarized light. The polarization directions of the second linear polarized light and the first linear polarized light are perpendicular. The second linear polarized light is reflected out of the optical path by another polarizer. The isolation effect can be known by measuring the light 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 closed-loop metamaterial. The isolation degree is obtained by testing 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 closed-loop 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, and the two transmittances are averaged to obtain the insertion loss along the diagonal direction of the periodic unit of the closed-loop 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, characterized in that The wire grid is made of tungsten wire.

8. The system according to claim 4, characterized in that 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, characterized in that The insertion loss, isolation and blocking bandwidth of the system can be adjusted by adjusting the length and width of the metal ring, the length of the first metal arm and the second metal arm, and the thickness of the first dielectric layer, the second dielectric layer and the third dielectric layer.

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