Magnetic-free terahertz isolator and control method for defective grating metasurface

Abstract

This invention discloses a magnetless terahertz isolator with a defective grating metasurface and its control method, belonging to the field of terahertz devices. The terahertz isolator is composed of several periodically spliced ​​unit structures, each unit structure including a silicon dioxide substrate and a silicon metasurface containing a defective grating. This invention utilizes the combination of material nonlinearity and the asymmetry of the metasurface structure to adjust the non-reciprocal intensity by changing structural parameters, thereby achieving non-reciprocal transmission control of terahertz waves. The magnetless terahertz isolator designed in this invention has a simple structure, low operating power, and requires no external magnetic field bias, making it suitable for future terahertz integrated systems.

Description

Technical Field

[0001] This invention relates to terahertz isolators, and more particularly to a non-magnetic terahertz isolator with a defective grating metasurface and a control method thereof. Background Technology

[0002] Terahertz waves (THz) refer to a segment of electromagnetic waves with frequencies ranging from 0.1 THz to 10 THz. Positioned between microwaves and the infrared band in the electromagnetic spectrum, and with wavelengths between electronics and optics, terahertz waves possess some characteristics of both microwaves and the infrared band. Compared to microwaves and infrared light waves, terahertz waves are non-ionizing, broadband, and have low absorption in non-polar materials. The terahertz frequency is often referred to as the "THz Gap" because it lies between microwave and infrared electromagnetic energy, presenting numerous obstacles and difficulties that have hindered scientists and engineers from exploring its spectral patterns. Currently, terahertz waves are widely studied in biomedicine, materials identification, spectroscopy, and imaging, and the study of the terahertz spectrum has significant scientific value and application prospects. Terahertz functional devices are crucial for these applications. Among them, terahertz isolators allow only forward electromagnetic waves to pass through, prohibiting reverse electromagnetic waves. This non-reciprocal unidirectional conduction device, analogous to an electrical diode, is one of the fundamental unit components of future terahertz systems. It holds significant value in protecting terahertz sources, eliminating multipath interference, and suppressing unwanted terahertz signals, making it crucial for the construction and implementation of various terahertz systems. Traditional terahertz isolators rely on terahertz magneto-optical effects and Faraday rotation effects. However, neither the magneto-optical materials nor the magnets used to generate the magnetic field are compatible with current large-scale semiconductor integration processes, resulting in most terahertz isolators being bulky and having strong bias magnetic fields. Therefore, developing magnet-free terahertz isolators is of great importance for achieving terahertz system integration. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing technologies, such as difficulty in integration and complex structure, and to provide a non-magnetic terahertz isolator with a defective grating metasurface.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] In a first aspect, the present invention provides a magnetic-free terahertz isolator based on a defective grating metasurface. The magnetic-free terahertz isolator is composed of a plurality of defective grating metasurface unit structures arranged periodically and spliced ​​together. The defective grating metasurface unit structure includes a substrate and a base grating. The base grating consists of a grating bottom layer and a first grating and a second grating arranged parallel to the grating bottom layer. A defect is provided along the entire length of the second grating at the apex near the side of the first grating. The cross-sectional shape of the first grating is rectangular, and the cross-sectional shape of the second grating is a right-angled step shape. The width of the first grating is the same as the maximum width of the second grating, and the thickness of the first grating is the same as the maximum thickness of the second grating. The magnetic-free terahertz isolator uses the contact surface between the substrate and air as the first port and the contact surface between the base grating and air as the second port.

[0006] As a preferred embodiment of the first aspect above, the thickness of the substrate is 40 μm to 70 μm.

[0007] As a preferred embodiment of the first aspect, the thickness of the base grating is 20μm to 60μm, the thickness of the grating bottom layer is 5μm to 20μm, the spacing between the first grating and the second grating is 10μm to 30μm, the width of the first grating and the maximum width of the second grating are both 30μm to 50μm, and the defect depth on the second grating is 25μm to 38μm, and the defect width is 10μm to 25μm.

[0008] As a preferred embodiment of the first aspect above, the period of the defect grating metasurface unit structure is 200 μm to 300 μm.

[0009] As a preferred embodiment of the first aspect, the spacing between the first grating and the second grating between adjacent defect grating metasurface unit structures is 10 μm to 30 μm.

[0010] As a preferred embodiment of the first aspect above, the substrate is made of silicon dioxide.

[0011] As a preferred embodiment of the first aspect above, the base grating is made of silicon, and silicon has a nonlinear refractive index n2 = 1.12 × 10⁻⁶. -12 cm 2 / W.

[0012] In a second aspect, the present invention provides a control method for a non-magnetic terahertz isolator as described in any of the embodiments of the first aspect above, which includes two control modes: linear condition and nonlinear condition.

[0013] Under linear conditions, terahertz wave transmission can be achieved from the first port to the second port and from the second port to the first port. Therefore, this non-magnetic terahertz isolator structure cannot achieve non-reciprocal transmission.

[0014] Under nonlinear conditions, by adjusting the intensity of the incident light, terahertz waves can be transmitted from the first port to the second port, but cannot be transmitted from the second port to the first port. Thus, this non-magnetic terahertz isolator structure can achieve non-reciprocal transmission and achieve the purpose of terahertz wave isolation.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] This invention designs a non-magnetic terahertz isolator based on a defective grating metasurface. It utilizes the combination of material nonlinearity and metasurface structural asymmetry to adjust the non-reciprocal intensity by changing structural parameters, thereby achieving non-reciprocal transmission control of terahertz waves. The non-magnetic terahertz isolator designed in this invention has a simple structure, low operating power, and requires no external magnetic field bias, making it suitable for future terahertz integrated systems. Attached Figure Description

[0017] Figure 1 These are schematic diagrams of the three-dimensional (a) and two-dimensional (b) structures of the non-magnetic terahertz isolator with a defective grating metasurface;

[0018] Figure 2 It is a function of the transmission coefficient and frequency of the defective grating metasurface under linear and nonlinear conditions;

[0019] Figure 3 The input light intensity is 0.01-10 MW / cm² at the operating frequency of 0.4321 THz. 2 Transmission spectra at each port within the range;

[0020] Figure 4 It is a function of the isolation degree of the non-magnetic terahertz isolator of the defective grating metasurface and the input light intensity;

[0021] Figure 5 It is a function of the insertion loss of the non-magnetic terahertz isolator of the defective grating metasurface and the input light intensity. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in the various embodiments of the present invention can be combined accordingly without mutual conflict.

[0023] like Figure 1As shown in Figure (a), in one embodiment of the present invention, a magnetic-free terahertz isolator based on a defective grating metasurface is provided. The magnetic-free terahertz isolator is formed by periodically arranging and splicing several defective grating metasurface unit structures. Each defective grating metasurface unit structure is identical and is periodically repeated on a plane to form the magnetic-free terahertz isolator. Figure 1 The diagram shows the configuration of two defective grating metasurface unit structures spliced ​​together, but the specific number of defective grating metasurface unit structures spliced ​​together needs to be set according to the actual device size and is not a limitation.

[0024] like Figure 1 As shown in (b), each defective grating metasurface unit structure includes a substrate 3 and a base grating. The base grating consists of a grating bottom layer 4 and a first grating 5 and a second grating 6 arranged on the grating bottom layer 4. The first grating 5 and the second grating 6 are arranged in parallel on the grating bottom layer 4, and their lengths along the grating extension direction are not limited and can be adjusted according to the actual device size. A defect 7 is provided at the apex of the second grating 6 near the side of the first grating 5, and the defect 7 is provided along the entire length of the second grating 6. The cross-sectional dimension of the defect 7 is rectangular. The cross-sectional shape of the first grating 5 is rectangular, and the cross-section of the second grating 6 before the defect 7 is formed can also be regarded as the same rectangle as the cross-section of the first grating 5. Therefore, after the defect 7 is formed, the cross-sectional shape of the second grating 6 is a right-angled step shape. In addition, for the right-angled step shape, its width and thickness are different at different positions, and the width and thickness are the largest in the part without the defect 7. In this defective grating metasurface unit structure, the width of the first grating 5 is the same as the maximum width of the second grating 6, and the thickness of the first grating 5 is the same as the maximum thickness of the second grating 6. This non-magnetic terahertz isolator uses the contact surface between the substrate 3 and air as the first port 1, and the contact surface between the base grating and air as the second port 2.

[0025] For ease of description, the present invention defines... Figure 1 In the diagram, the x-direction represents the width, the z-direction represents the thickness, and the y-direction represents the grating extension direction. Therefore, the specific materials and parameters of the non-magnetic terahertz isolator based on this defective grating metasurface are as follows:

[0026] The thickness of substrate 3 is 40 μm to 70 μm. The thickness of the base grating (based on the maximum thickness of the base grating) is 20 μm to 60 μm, of which the thickness of the bottom layer grating 4 is 5 μm to 20 μm. In the defect grating metasurface unit structure, the spacing between the first grating 5 and the second grating 6 is 10 μm to 30 μm; the width of the first grating 5 and the maximum width of the second grating 6 are both 30 μm to 50 μm; the depth of the defect 7 on the second grating 6 is 25 μm to 38 μm, and the width of the defect 7 is 10 μm to 25 μm. The period (i.e., the width of the unit structure in the x-direction) of the defect grating metasurface unit structure is 200 μm to 300 μm. The spacing between the first grating 5 and the second grating 6 on both sides of the splicing position between adjacent defect grating metasurface unit structures is also 10 μm to 30 μm. Therefore, the spacing between any adjacent first grating 5 and second grating 6 on the entire magnetically free terahertz isolator metasurface is the same. Substrate 3 is made of silicon dioxide. The base grating is made of silicon, with a nonlinear refractive index n² = 1.12 × 10⁻⁶. -12 cm 2 / W.

[0027] In addition, the present invention also provides a control method for the above-mentioned non-magnetic terahertz isolator, which includes two control modes: linear condition and nonlinear condition.

[0028] Under linear conditions, terahertz wave transmission can be achieved from the first port 1 to the second port 2 and from the second port 2 to the first port 1. Therefore, the non-magnetic terahertz isolator structure cannot achieve non-reciprocal transmission.

[0029] Under nonlinear conditions, by adjusting the intensity of the incident light, terahertz waves can be transmitted from the first port 1 to the second port 2, but cannot be transmitted from the second port 2 to the first port 1. Thus, this non-magnetic terahertz isolator structure can achieve non-reciprocal transmission and achieve the purpose of terahertz wave isolation.

[0030] The following example demonstrates the effectiveness of the non-magnetic terahertz isolator based on the aforementioned defective grating metasurface.

[0031] Example

[0032] In this embodiment, the shapes of each component of the non-magnetic terahertz isolator of the defective grating metasurface are as described above, see details below. Figure 1 Further details will not be elaborated here. The specific parameters of each component in this example are as follows:

[0033] The substrate 3 has a thickness of 55 μm. The base grating has a thickness of 50 μm, with the bottom layer 4 having a thickness of 12 μm. In the defect grating metasurface unit structure, the spacing between the first grating 5 and the second grating 6 is 25 μm; the width of the first grating 5 and the maximum width of the second grating 6 are both 50 μm; the depth of the defect 7 on the second grating 6 is 30 μm, and the width of the defect 7 is 25 μm. The period of the defect grating metasurface unit structure is 300 μm. The spacing between the first grating 5 and the second grating 6 on both sides of the splicing position between adjacent defect grating metasurface unit structures is also 25 μm. The spacing between any adjacent first grating 5 and second grating 6 on the entire magnetic-free terahertz isolator metasurface is 25 μm. The substrate 3 is made of silicon dioxide. The base grating is made of silicon, with a nonlinear refractive index n2 = 1.12 × 10⁻⁶. -12 cm 2 / W.

[0034] This embodiment simulates the aforementioned non-magnetic terahertz isolator to demonstrate its technical effectiveness. Since the length along the defect grating extension direction is arbitrary, a 2D model can be used to simulate the real structure in the simulation calculation. The incident light conditions at the ports are used to excite the metasurface structure. Theoretically, the nonlinear response of the material will change the refractive index of the structure, leading to a frequency shift. Due to the asymmetry of the structure in the excitation direction, the nonlinear shifts from opposite excitation directions are different, thus achieving non-reciprocal propagation of terahertz waves and ultimately achieving terahertz wave isolation. The transmission coefficient as a function of frequency is obtained by exciting each port (the first port 1 is denoted as port1, and the second port 2 is denoted as port2) under both linear and nonlinear conditions, as shown in the simulation. Figure 2 As shown. Under linear conditions, the transmission spectra obtained from the first port 1 and the second port 2 are indistinguishable, and this structure cannot achieve non-reciprocal transmission. Under nonlinear conditions, the transmission spectra obtained from the first port 1 and the second port 2 show a significant difference, achieving non-reciprocal transmission. By adjusting the incident light intensity, the non-reciprocal response obtained at the resonant frequency of the two ports is the strongest, that is, the best effect of terahertz wave isolation is achieved. The defective grating metasurface structure has an input light intensity of 0.01-10 MW / cm at a frequency of 0.4321. 2 Transmission spectra of each port in the range, such as Figure 3 As shown, the transmission spectrum at both ports first increases and then decreases with increasing incident light intensity. The relationship between the isolation degree of the obtained defective grating metasurface-based non-magnetic terahertz isolator and the input light intensity is as follows: Figure 4 As shown, the incident light intensity reaches 0.5 MW / cm². 2 At that time, the isolation of the structure reached its maximum value of 12.08 dB. The insertion loss of the non-magnetic terahertz isolator with defective grating metasurface as a function of input light intensity is as follows: Figure 5 As shown, when the light intensity is 0.5 MW / cm 2At that time, the insertion loss of the silicon grating metasurface was 4.7 dB. The results show that the designed defective grating metasurface-based non-magnetic terahertz isolator can achieve non-reciprocal propagation of terahertz waves and has good isolation performance.

[0035] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A non-magnetic terahertz isolator based on a defective grating metasurface, characterized in that, It is composed of several defective grating metasurface unit structures arranged and spliced ​​periodically; the defective grating metasurface unit structure includes a substrate (3) and a base grating. The base grating consists of a grating bottom layer (4) and a first grating (5) and a second grating (6) arranged in parallel on the grating bottom layer (4). The grating bottom layer (4) is a layer attached to the substrate (3), and a defect (7) is provided along the entire length of the apex of the second grating (6) near the side of the first grating (5). The cross-sectional shape of the first grating (5) is rectangular, and the cross-sectional shape of the second grating (6) is a right-angled step shape. The width of the first grating (5) is the same as the maximum width of the second grating (6), and the thickness of the first grating (5) is the same as the maximum thickness of the second grating (6). The magnetic-free terahertz isolator takes the contact surface between the substrate (3) and the air as the first port (1) and the contact surface between the base grating and the air as the second port (2).

2. The non-magnetic terahertz isolator with a defective grating metasurface according to claim 1, characterized in that, The thickness of the substrate (3) is 40μm~70μm.

3. The non-magnetic terahertz isolator with a defective grating metasurface according to claim 1, characterized in that, The maximum thickness of the base grating is 20μm~60μm, and the thickness of the bottom layer (4) of the grating is 5μm~20μm; the spacing between the first grating (5) and the second grating (6) is 10μm~30μm; the maximum width of the first grating (5) and the second grating (6) is 30μm~50μm; the depth of the defect (7) on the second grating (6) is 25μm~38μm, and the width of the defect (7) is 10μm~25μm.

4. The non-magnetic terahertz isolator with a defective grating metasurface according to claim 1, characterized in that, The period of the defect grating metasurface unit structure is 200μm~300μm.

5. A non-magnetic terahertz isolator with a defective grating metasurface according to claim 1, characterized in that, The spacing between the first grating (5) and the second grating (6) between adjacent defect grating metasurface unit structures is 10μm~30μm.

6. The non-magnetic terahertz isolator with a defective grating metasurface according to claim 1, characterized in that, The substrate (3) is made of silicon dioxide.

7. A non-magnetic terahertz isolator with a defective grating metasurface according to claim 1, characterized in that, The base grating is made of silicon, and silicon has a nonlinear refractive index n² = 1.12 × 10⁻⁶. -12 cm 2 / W.

8. A control method for the non-magnetic terahertz isolator as described in claim 1, characterized in that, It includes two control modes: linear condition and nonlinear condition; Under linear conditions, terahertz wave transmission can be achieved from the first port (1) to the second port (2) and from the second port (2) to the first port (1), thus the non-magnetic terahertz isolator structure cannot achieve non-reciprocal transmission; Under nonlinear conditions, by adjusting the intensity of the incident light, terahertz waves can be transmitted from the first port (1) to the second port (2), but cannot be transmitted from the second port (2) to the first port (1). Thus, the non-magnetic terahertz isolator structure can achieve non-reciprocal transmission and achieve the purpose of terahertz wave isolation.

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