Terahertz isolator based on time barrier metasurface

Abstract

The invention discloses a terahertz isolator based on a time barrier metasurface, which is arranged on a substrate, two sides of the substrate are respectively provided with an x polaroid and a y polaroid, the terahertz isolator comprises a plurality of metasurface structure units, and the metasurface structure units are arranged on one side, close to the y polaroid, of the substrate. The metasurface structure unit comprises a metal rod, a first opening resonance ring, a second opening resonance ring, a third opening resonance ring, a fourth opening resonance ring, a first semiconductor structure and a second semiconductor structure. According to the terahertz isolator based on the time barrier metasurface disclosed by the invention, in transient polarization conversion, the coherent cancellation state of two pairs of original resonance modes is broken by phase shift caused by the time barrier to cause terahertz energy radiation, and the coherent cancellation state in the other direction is protected by an incident field to cause terahertz energy radiation. And the effect of the time loss barrier is invalid, so that unidirectional terahertz transmission is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz isolation, and in particular relates to a terahertz isolator based on a time barrier metasurface. Background Art

[0002] Terahertz waves are between microwaves and infrared waves, with a frequency range of 0.1-10THz and a wavelength of 0.03-3mm. They are expected to unlock wireless connections with terabits per second, which is crucial for future 6G communications. They have a wide range of applications in imaging, sensing, and other fields. Non-reciprocal terahertz devices, such as isolators or circulators, help protect terahertz sources, mitigate multipath interference, and achieve stable communications. Traditional terahertz non-reciprocal devices are mostly realized through the Faraday effect and the magneto-optical Kerr effect, or by utilizing the inherent non-reciprocal directional dichroism in magnetic materials. However, the magneto-optical effect is weak in the terahertz frequency band. In addition, the above schemes rely on external magnetic fields, as well as long interaction lengths and low-temperature environments, and cannot be integrated into modern optical systems. Summary of the invention

[0003] The main purpose of the present invention is to provide a terahertz isolator based on a time barrier metasurface, which can achieve the effect of isolating specific frequencies in the terahertz band without applying extreme conditions such as low temperature and strong magnetic field. Different from time-space modulation, the present invention breaks the coupling between polarization-related modes in an ultra-short time by uniformly and suddenly changing its electromagnetic properties in space, thereby realizing a time barrier that can cause ultrafast phase changes between two resonant modes. In transient polarization conversion, the coherent destructive state of the original two pairs of resonant modes is broken by the time barrier, resulting in terahertz energy radiation, while the coherent destructive state in the other direction is protected by the incident field, and the effect of the time loss barrier is invalid, thereby achieving unidirectional terahertz transmission.

[0004] To achieve the above objectives, the present invention provides a terahertz isolator based on a time barrier metasurface, which is arranged on a substrate, and an x ​​polarizer and a y polarizer are respectively arranged on both sides of the substrate, including a plurality of metasurface structure units, and the metasurface structure units are located on the side of the substrate close to the y polarizer, and the metasurface structure units include a metal rod, a first open resonant ring, a second open resonant ring, a third open resonant ring, a fourth open resonant ring, a first semiconductor structure and a second semiconductor structure, wherein:

[0005] The first open resonant ring and the second open resonant ring are connected to a first side of the metal rod, and the third open resonant ring and the fourth open resonant ring are connected to a second side of the metal rod, the first open resonant ring and the third open resonant ring are located at the same level, and the second open resonant ring and the fourth open resonant ring are located at the same level; the first semiconductor structure covers the second open resonant ring, and the second semiconductor structure covers the third open resonant ring;

[0006] The isolation principle of terahertz isolator is:

[0007] When the pump light acts on the first semiconductor structure and the second semiconductor structure, the conductivity of the (semiconductor Ge) increases instantaneously, so that the open resonant ring mode of the second open resonant ring covering the first semiconductor structure (Ge film) and the open resonant ring mode of the third open resonant ring covering the second semiconductor structure are weakened, and at the same time, the phase changes transiently, and the open resonant ring mode and phase of the first open resonant ring and the fourth open resonant ring without covering (Ge film) remain unchanged;

[0008] The terahertz pulse incident on the y-polarizer couples the y-polarized energy to the split resonant ring through the metal rod, and the resonant modes of the two pairs of split resonant rings produce coherent destructive behavior. When the pump light and the terahertz pulse reach the metasurface structure unit at the same time, the transient phase change of the second and third split resonant rings breaks the coherent destructive state, and radiates the terahertz signal in the form of x-polarization, thereby achieving the transmission of the forward terahertz y-polarization to x-polarization signal.

[0009] The terahertz pulse incident on the x-polarizer in reverse excites two pairs of open ring resonant modes. Although the open ring resonant modes covering the semiconductor structure will be weakened, the phase is protected by the external field. The two pairs of open ring resonant modes are coupled to the metal rod with the same energy. Since the phase of the coupling with the metal rod is opposite, the y polarization mode is canceled and no energy is radiated, resulting in the obstruction of reverse incidence, thereby realizing unidirectional terahertz transmission.

[0010] As a further preferred technical solution of the above technical solution, the material of the first semiconductor structure and the second semiconductor structure is amorphous germanium (Ge).

[0011] As a further preferred technical solution of the above technical solution, the material of the metal rod, the first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring is gold (Au, ultra-high conductivity).

[0012] As a further preferred technical solution of the above technical solution, the opening direction of the first open resonant ring is opposite to the opening direction of the second open resonant ring, and the opening direction of the third open resonant ring is opposite to the opening direction of the fourth open resonant ring.

[0013] As a further preferred technical solution of the above technical solution, the opening direction of the first open resonant ring is the same as the opening direction of the third open resonant ring. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the super surface structural unit of the present invention.

[0015] Figure 2 It is a schematic diagram of the change in conductivity of the semiconductor Ge of the present invention under the excitation of different optical pump powers.

[0016] Figure 3 It is a working principle diagram of the present invention.

[0017] Figure 4 It is a simulated transmission spectrum of the present invention.

[0018] Figure 5 This is the experimental transmission spectrum of the present invention.

[0019] The reference numerals include: 1. metal rod; 2. first open resonant ring; 3. second open resonant ring; 4. third open resonant ring; 5. fourth open resonant ring; 6. first semiconductor structure; 7. second semiconductor structure. DETAILED DESCRIPTION

[0020] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0021] In the preferred embodiment of the present invention, those skilled in the art should note that the terahertz signal and the like involved in the present invention may be regarded as prior art.

[0022] Preferred embodiments.

[0023] like Figure 1-5 As shown, the present invention discloses a terahertz isolator based on a time barrier metasurface, which is arranged on a substrate, and an x ​​polarizer and a y polarizer are respectively arranged on both sides of the substrate, including a plurality of metasurface structure units, and the metasurface structure units are located on the side of the substrate close to the y polarizer, and the metasurface structure units include a metal rod, a first open resonant ring, a second open resonant ring, a third open resonant ring, a fourth open resonant ring, a first semiconductor structure and a second semiconductor structure, wherein:

[0024] The first open resonant ring and the second open resonant ring are connected to a first side of the metal rod, and the third open resonant ring and the fourth open resonant ring are connected to a second side of the metal rod, the first open resonant ring and the third open resonant ring are located at the same level, and the second open resonant ring and the fourth open resonant ring are located at the same level; the first semiconductor structure covers the second open resonant ring, and the second semiconductor structure covers the third open resonant ring;

[0025] The isolation principle of terahertz isolator is:

[0026] When the pump light acts on the first semiconductor structure and the second semiconductor structure, the conductivity of the (semiconductor Ge) increases instantaneously, so that the open resonant ring mode of the second open resonant ring covering the first semiconductor structure (Ge film) and the open resonant ring mode of the third open resonant ring covering the second semiconductor structure are weakened, and at the same time, the phase changes transiently, and the open resonant ring mode and phase of the first open resonant ring and the fourth open resonant ring without covering (Ge film) remain unchanged;

[0027] The terahertz pulse incident on the y polarizer couples the y polarization energy to the open resonant ring through the metal rod, and the resonant modes of the two pairs of open resonant rings produce coherent destructive (one pair refers to the first and fourth open resonant rings, and the other pair refers to the second and third open resonant rings). When the pump light and the terahertz pulse reach the metasurface structure unit at the same time, the transient phase change of the second and third open resonant rings breaks the coherent destructive state, and radiates the terahertz signal in the form of x polarization, thereby realizing the transmission of the forward terahertz y polarization to x polarization signal;

[0028] The terahertz pulse incident on the x-polarizer in reverse excites two pairs of open ring resonant modes. Although the open ring resonant modes covering the semiconductor structure will be weakened, the phase is protected by the external field. The two pairs of open ring resonant modes are coupled to the metal rod with the same energy. Since the phase of the coupling with the metal rod is opposite, the y polarization mode is canceled and no energy is radiated, resulting in the obstruction of reverse incidence, thereby realizing unidirectional terahertz transmission.

[0029] Specifically, the materials of the first semiconductor structure and the second semiconductor structure are amorphous germanium (Ge).

[0030] More specifically, the metal rod, the first split resonant ring, the second split resonant ring, the third split resonant ring and the fourth split resonant ring are made of gold (Au, ultra-high conductivity), and other high-conductivity metals may also be used.

[0031] In this embodiment, the working process of the present invention is illustrated by an example of a metal-semiconductor hybrid metasurface terahertz isolator operating at a frequency of about 0.7 THz:

[0032] The time barrier metasurface structural unit consists of four metal split resonant rings, metal rods and semiconductor square arrays, such as Figure 1 As shown, the specific parameters are: p x =100 μm (the length of the supersurface structure unit), p y =140μm (width of the metasurface structure unit). Lx1 (total length of the open resonant ring) = Ly1 (total width of the open resonant ring) = 37μm, Lx2 (length of the semiconductor structure) = 41μm, Ly2 (width of the semiconductor structure) = 45.5μm, w1 (width of the metal rod) = 6μm, w2 (bottom width of the open resonant ring) = 4μm, g (opening width of the open resonant ring) = 4μm, h (length of the bent metal part of the open resonant ring) = 24μm. The semiconductor used is amorphous germanium (Ge), and the metal material is ultra-high conductivity material gold (Au), with a thickness of 200nm. The conductivity of Ge is determined by the power of the pump light, such as Figure 2 shown.

[0033] The device uses a transient time-loss barrier to break the time-reversal symmetry of terahertz passing through the device, achieving non-reciprocal unidirectional isolated transmission. Figure 4 As shown in the figure, the device simulation can achieve 20dB isolation in the 0.4THz range, and close to 60dB isolation in the 0.7THz range, with an insertion loss of 15dB. Figure 5 As shown, an isolation greater than 30dB is achieved.

[0034] Compared with the previous method of using magnetic materials to achieve non-reciprocal transmission, this device uses a time barrier metasurface to realize terahertz isolation devices. This device does not require an external magnetic field, and has no special requirements for ambient temperature and humidity, and can work at room temperature. If the control end of the semiconductor conductivity in the metasurface is replaced by circuit control instead of external light field pumping, the device's integration will be further enhanced.

[0035] For the present invention, the measured isolation ratio is as high as 30dB at 0.7THz, which can be controlled by adjusting the pump power. No extreme conditions such as low temperature and magnetic field are required; the processing technology of the metasurface is compatible with the current CMOS process, providing an opportunity to build miniaturized, integrable, non-magnetic non-reciprocal devices.

[0036] It is worth mentioning that the technical features such as terahertz signals involved in the patent application of this invention should be regarded as prior art. The specific structure, working principle and possible control method and spatial arrangement method of these technical features can be selected by conventional methods in the field, and should not be regarded as the inventive point of this patent. This patent will not be further elaborated.

[0037] For those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A terahertz isolator based on a time barrier metasurface, arranged on a substrate, with an x ​​polarizer and a y polarizer respectively arranged on both sides of the substrate, characterized in that: The method comprises a plurality of metasurface structure units, and the metasurface structure units are located on a side of the substrate close to the y polarizer, and the metasurface structure units include a metal rod, a first split resonant ring, a second split resonant ring, a third split resonant ring, a fourth split resonant ring, a first semiconductor structure, and a second semiconductor structure, wherein: The first open resonant ring and the second open resonant ring are connected to a first side of the metal rod, and the third open resonant ring and the fourth open resonant ring are connected to a second side of the metal rod, the first open resonant ring and the third open resonant ring are located at the same level, and the second open resonant ring and the fourth open resonant ring are located at the same level; the first semiconductor structure covers the second open resonant ring, and the second semiconductor structure covers the third open resonant ring; The isolation principle of terahertz isolator is: When the pump light acts on the first semiconductor structure and the second semiconductor structure, the conductivity increases instantaneously, so that the open resonant ring mode of the second open resonant ring covering the first semiconductor structure and the open resonant ring mode of the third open resonant ring covering the second semiconductor structure are weakened, and at the same time, the phase changes transiently, and the open resonant ring mode and phase of the uncovered first open resonant ring and the fourth open resonant ring remain unchanged; The terahertz pulse incident on the y-polarizer couples the y-polarized energy to the split resonant ring through the metal rod, and the resonant modes of the two pairs of split resonant rings produce coherent destructive behavior. When the pump light and the terahertz pulse reach the metasurface structure unit at the same time, the transient phase change of the second and third split resonant rings breaks the coherent destructive state, and radiates the terahertz signal in the form of x-polarization, thereby achieving the transmission of the forward terahertz y-polarization to x-polarization signal. The terahertz pulse incident on the x-polarizer in reverse excites two pairs of open ring resonant modes. Although the open ring resonant modes covering the semiconductor structure will be weakened, the phase is protected by the external field. The two pairs of open ring resonant modes are coupled to the metal rod with the same energy. Since the phase of the coupling with the metal rod is opposite, the y polarization mode is canceled and no energy is radiated, resulting in the obstruction of reverse incidence, thereby realizing unidirectional terahertz transmission.

2. A terahertz isolator based on a time barrier metasurface according to claim 1, characterized in that: The materials of the first semiconductor structure and the second semiconductor structure are amorphous germanium.

3. A terahertz isolator based on a time barrier metasurface according to claim 2, characterized in that: The material of the metal rod, the first split resonant ring, the second split resonant ring, the third split resonant ring and the fourth split resonant ring is gold.

4. The terahertz isolator based on a time barrier metasurface according to claim 3, characterized in that: The opening direction of the first split resonant ring is opposite to the opening direction of the second split resonant ring, and the opening direction of the third split resonant ring is opposite to the opening direction of the fourth split resonant ring.

5. The terahertz isolator based on a time barrier metasurface according to claim 4, characterized in that: The opening direction of the first split resonant ring is the same as the opening direction of the third split resonant ring.

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