Terahertz vortex phase plate based on dumbbell-shaped metasurface

Abstract

The invention discloses a terahertz vortex phase plate based on a dumbbell-shaped metasurface. A plurality of metasurface units arranged on the same plane; the metasurface unit comprises a top basic unit metal structure layer, a middle dielectric layer and a substrate metal reflecting surface layer; the top basic unit metal structure layer is of a dumbbell-shaped structure, and the area is smaller than that of the middle dielectric layer and the base metal reflecting surface layer; the positions of all layers of the multiple metasurface units are correspondingly arranged, the phase distribution of the arranged multiple top layer basic unit metal structure layers on the plane meets the vortex beam phase distribution, and a metasurface array with the target topological charge is formed; the metasurface array is a terahertz wave incident plane. On the basis of improving the working efficiency, the metasurface technology and the geometric phase principle are combined, the whole-column arrangement of the terahertz vortex phase plate and the generation of terahertz vortex light beams with different topological charges are completed by designing a reflection type basic unit structure, and then the phase coverage corresponding to the specified topological charges is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz functional devices, and in particular to a terahertz vortex phase plate based on a dumbbell-shaped metasurface. Background Art

[0002] The vigorous development of terahertz in various fields has made the research on various terahertz devices more urgent, because in various terahertz systems, the intensity, phase, polarization and other properties of terahertz waves need to be regulated, and most optical band devices cannot be directly used in terahertz systems because their materials have too high losses in the terahertz band. Therefore, it is necessary to select suitable materials and processes to make terahertz devices.

[0003] In order to meet the needs of ultra-wideband and large-capacity 6G wireless communications in the future, terahertz vortex beams are one of the most promising technologies. Terahertz vortex beams combine the advantages of terahertz waves and vortex beams while having large bandwidth and adding a degree of freedom in communication. They are expected to greatly improve the communication capacity of radar communication systems and the resolution of imaging systems. Terahertz vortex beam control devices designed using traditional methods are easy to implement, but these devices have problems such as large size, high price, and inability to transmit information over long distances. Compared with traditional methods of generating vortex beams, metasurfaces can produce phase mutations in incident light through nanostructures, and independently control dynamic or geometric phases at the nanoscale to generate vortices. Metasurfaces are ultra-thin planar devices composed of artificial microstructures that can achieve control of the amplitude, phase, and polarization state of electromagnetic waves. They have the advantages of small size, light weight, high integration, and flexible control of electromagnetic waves, and play a huge role in electromagnetic spectrum and wavefront modulation. By introducing metasurfaces into terahertz-band vortex beams and utilizing the metasurface's ability to regulate electromagnetic waves, a variety of terahertz functional devices can be realized, thereby effectively solving the hot issue of how to generate efficient vortex beams in the terahertz band in practical applications.

[0004] In recent years, most devices that generate terahertz vortex beams are limited to topological charges of 1 and 2. Since the technology of increasing the topological charge of terahertz vortex phase plates is difficult, there are few studies on terahertz vortex beam control devices with larger topological charges (l≥3). The use of transmissive metasurfaces to generate terahertz vortex beams has the problem of low transmittance and low work efficiency. Efficient generation of terahertz vortex beams is a bottleneck that needs to be broken through in the fields of particle manipulation, optical processing, optical communication, optical imaging, etc. At present, there is still a lack of effective modulation devices in the terahertz band.

[0005] Therefore, how to provide a terahertz vortex phase plate that can achieve efficient generation of high-order topological charge terahertz vortex beams is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the invention

[0006] In view of the problems that the existing transmission-type metasurface has low efficiency in regulating terahertz wave vortex beams and there is little research on terahertz vortex beams with high-order topological charge numbers, the present invention provides a terahertz vortex phase plate based on a dumbbell-shaped metasurface. On the basis of improving working efficiency, the metasurface technology and the geometric phase principle are combined to complete the entire arrangement of the terahertz vortex phase plate by designing a reflective basic unit structure, thereby generating terahertz vortex beams with different topological charges, and further achieving phase coverage corresponding to a specified topological charge number.

[0007] The present invention provides a terahertz vortex phase plate based on a dumbbell-shaped metasurface, comprising: a plurality of metasurface units arranged in the same plane; wherein:

[0008] The metasurface unit comprises: a top basic unit metal structure layer, an intermediate dielectric layer and a base metal reflective surface layer; the top basic unit metal structure layer is a dumbbell-shaped structure, and its area is smaller than that of the intermediate dielectric layer and the base metal reflective surface layer;

[0009] The positions of each layer of the multiple metasurface units are arranged correspondingly, and the phase distribution of the multiple top-level basic unit metal structure layers on the plane after arrangement satisfies the vortex beam phase distribution, forming a metasurface array with a target topological charge number; the metasurface array is a terahertz wave incident surface.

[0010] The present invention utilizes the principle of geometric phase, forms a metasurface array with different topological charges by rotating the basic unit structure, designs a terahertz vortex phase plate, and thus realizes the generation of terahertz vortex beams with different topological charges.

[0011] Preferably, based on the finite element method, combined with the target relationship between the phase distribution required by the unit position (x, y) of the top basic unit metal structure layer in the metasurface array and the azimuth angle around the center point of the metasurface array, the phase distribution of the top basic unit metal structure layer in the metasurface array is calculated to satisfy the vortex beam phase distribution formula:

[0012]

[0013] in, is the phase that the top basic unit metal structure layer needs to satisfy at the unit position (x, y) of the metasurface array, and l is the topological charge number.

[0014] Preferably, the topological charge is ≥3.

[0015] Preferably, the dumbbell-shaped structure includes: two semicircular structures and a rectangular structure; the diameter sides of the two semicircular structures are opposite and respectively connected to the two short sides of the rectangular structure, and the central axis of the rectangular structure passes through the center of the two semicircular structures to form an integrated dumbbell-shaped structure.

[0016] Preferably, the radius of the semicircular structure is 37 μm, the short side of the rectangle is 25 μm, and the long side of the rectangle is 27 μm.

[0017] Preferably, the intermediate dielectric layer is square with a side length of 100 μm.

[0018] Preferably, the base metal reflective surface layer is a square, and the side length thereof is equal to the side length of the intermediate dielectric layer.

[0019] Preferably, the thickness of the top basic unit metal structure layer is 1 μm, the thickness of the intermediate dielectric layer is 25 μm, and the thickness of the base metal reflective surface layer is 1 μm.

[0020] Preferably, the material of the top basic unit metal structure layer is metallic copper.

[0021] Preferably, the material of the intermediate dielectric layer is polyimide.

[0022] Preferably, the base metal reflective surface layer is made of metallic copper.

[0023] Compared with the prior art, it has the following beneficial effects:

[0024] The present invention proposes a new type of terahertz vortex phase plate based on dumbbell-shaped metasurface, which can generate vortex beams within a certain terahertz frequency range by utilizing the modulation capability of metasurface devices on terahertz waves. While generating terahertz vortex beams with larger topological charge numbers (l≥3), the efficient generation of terahertz vortex beams and a wider operating frequency are achieved, laying a foundation for subsequent research on the application of terahertz vortex beams.

[0025] The present invention has the advantages of small size, light weight, high integration, and the ability to flexibly control electromagnetic waves.

[0026] The present invention has wide adaptability, that is, the present invention can be used in existing terahertz time-domain spectroscopy systems or existing devices that can generate terahertz sources to explore the application of terahertz vortex beams, which is of great significance.

[0027] The present invention has unprecedented application effects, can further improve communication capacity, and utilize orbital angular momentum to develop terahertz broadband spectrum resources to achieve 6G performance such as ultra-high transmission rate, ultra-high spectrum efficiency, and ultra-high energy efficiency. It has a wide range of applications in multiple fields, including: terahertz broadband spectrum resource development, terahertz communication technology, terahertz detection and imaging technology, terahertz radar chip technology, terahertz biomedicine, terahertz optical processing, terahertz basic science, terahertz industrial detection and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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 prior art descriptions. Obviously, the drawings described below are only embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on the provided drawings without creative work.

[0029] Figure 1 A schematic diagram of the three-dimensional structure of a terahertz vortex phase plate based on a dumbbell-shaped metasurface provided in an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of the front structure of a terahertz vortex phase plate based on a dumbbell-shaped metasurface provided in an embodiment of the present invention;

[0031] Figure 3 A schematic diagram of the three-dimensional structure of a dumbbell-shaped metasurface unit structure provided by an embodiment of the present invention;

[0032] Figure 4 A schematic top view of a dumbbell-shaped metasurface unit structure provided by an embodiment of the present invention;

[0033] Figure 5 A schematic side view of a dumbbell-shaped metasurface unit structure provided by an embodiment of the present invention;

[0034] Figure 6 A graph of reflection amplitude simulation results and a graph of reflection phase simulation results for the dumbbell-shaped metasurface unit structure provided in an embodiment of the present invention under the condition of linear polarized light incidence;

[0035] Figure 7 A graph showing the simulation results of reflection amplitude and reflection phase under circularly polarized light incident conditions for the dumbbell-shaped metasurface unit structure provided in an embodiment of the present invention;

[0036] Figure 8 A schematic diagram of near-field simulation results of a terahertz vortex phase plate based on a dumbbell-shaped metasurface provided in an embodiment of the present invention under circularly polarized light incident conditions;

[0037] Fig. 9A schematic diagram of far-field simulation results of a terahertz vortex phase plate based on a dumbbell-shaped metasurface provided in an embodiment of the present invention under circularly polarized light incidence conditions. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] like Figure 1-2 As shown, the terahertz vortex phase plate based on the dumbbell-shaped metasurface disclosed in the embodiment of the present invention includes: a plurality of metasurface units arranged in the same plane; wherein the metasurface unit includes: a top basic unit metal structure layer 1, an intermediate dielectric layer 2 and a base metal reflection surface layer 3; the top basic unit metal structure layer 1 is a dumbbell-shaped structure, and its area is smaller than the intermediate dielectric layer 2 and the base metal reflection surface layer 3; the positions of each layer of the plurality of metasurface units are arranged correspondingly, and the phase distribution of the arranged plurality of top basic unit metal structure layers 1 on the plane satisfies the vortex beam phase distribution, forming a metasurface array of the target topological charge; the metasurface array is the terahertz wave incident surface.

[0040] The terahertz vortex phase plate in this embodiment is formed by arranging 16×16 metasurface units. By using the geometric phase principle, multiple top basic unit metal structure layers 1 are rotated to form a metasurface array with different topological charges, thereby generating terahertz vortex beams with different topological charges.

[0041] In one embodiment, based on the finite element method, combined with the target relationship between the phase distribution required by the unit position (x, y) of the top basic unit metal structure layer 1 in the metasurface array and the azimuth angle around the center point of the metasurface array, the phase distribution of the top basic unit metal structure layer 1 in the metasurface array is calculated to satisfy the vortex beam phase distribution formula:

[0042]

[0043] in, is the phase that the top basic unit metal structure layer 1 needs to satisfy at the unit position (x, y) of the metasurface array, and l is the topological charge number.

[0044] In one embodiment, the topological charge is ≥3.

[0045] In one embodiment, Figure 3As shown, the dumbbell-shaped structure includes: two semicircular structures and a rectangular structure; the diameter sides of the two semicircular structures are opposite and respectively connected to the two short sides of the rectangular structure, and the central axis of the rectangular structure passes through the center of the two semicircular structures to form an integrated dumbbell-shaped structure.

[0046] In one embodiment, Figure 4 As shown, the radius r of the semicircular structure is 37 μm, the short side a of the rectangle is 25 μm, and the long side b of the rectangle is 27 μm.

[0047] In one embodiment, Figure 4 As shown, the intermediate dielectric layer 2 is a square with a side length P of 100 μm.

[0048] In one embodiment, the base metal reflective surface layer 3 is a square, and the side length P thereof is equal to the side length of the intermediate dielectric layer 2 .

[0049] In one embodiment, Figure 5 As shown, the thickness d1 of the top basic unit metal structure layer 1 is 1 μm, the thickness d2 of the intermediate dielectric layer 2 is 25 μm, and the thickness d3 of the base metal reflective surface layer 3 is 1 μm.

[0050] In one embodiment, the material of the top basic unit metal structure layer 1 is copper, and its conductivity is 5.8×10 7 S / m.

[0051] In one embodiment, the material of the intermediate dielectric layer 2 is polyimide, and its dielectric constant is 3.5.

[0052] In one embodiment, the base metal reflective surface layer 3 is made of metal copper.

[0053] Combination Figures 1 to 5 There is a specific relationship between the phase distribution required for each unit position (x, y) and the azimuth angle around the center point. Tables 1 to 4 below give an example of the rotation angle corresponding to each unit structure in the terahertz vortex phase plate.

[0054] Table 1 shows the rotation angle parameters (1-4) corresponding to the top basic unit structure

[0055]

[0056] Table 2 shows the rotation angle parameters (5-8) corresponding to the top basic unit structure

[0057]

[0058]

[0059] Table 3 shows the rotation angle parameters (9-12) corresponding to the top basic unit structure

[0060]

[0061]

[0062] Table 4 shows the rotation angle parameters (13-16) corresponding to the top basic unit structure

[0063]

[0064] like Figure 6 As shown in the figure, the reflection amplitude and reflection phase simulation results at different frequencies are described when the terahertz linear x-polarized wave and the linear y-polarized wave are incident along the -z axis direction, that is, vertically toward the top basic unit metal structure layer. The left figure shows the reflection amplitude results at different frequencies, and the right figure shows the reflection phase results at different frequencies. The reflection amplitudes of the incident x-polarized light and y-polarized light in the wide frequency band of 0.91 to 1.92 THz are both greater than 0.95, and the reflection phase difference is close to 180°.

[0065] like Figure 7 As shown in the figure, the reflection amplitude and reflection phase simulation results of dumbbell-shaped units with different rotation angles under left-handed circularly polarized waves and right-handed circularly polarized waves are given. The upper two figures are the reflection amplitude and reflection phase simulation results of dumbbell-shaped units with different rotation angles under left-handed circularly polarized waves, and the lower two figures are the reflection amplitude and reflection phase simulation results of dumbbell-shaped units with different rotation angles under right-handed circularly polarized waves. In the frequency band of 0.91 to 1.92 THz, the unit structures with different rotation angles show basically consistent reflection amplitudes, and the amplitude values ​​are all greater than 0.9; and in the broadband working frequency band of 0.93 to 1.88 THz, the reflection amplitude is greater than 0.95. In the range of 0.91THz to 1.92THz, the phase difference between adjacent units is 45°, and the phase change is approximately equal to twice the rotation angle. These units with different rotation angles can achieve phase control of 0°, ±45°, ±90°, ±135°, ±180°, ±225°, ±270° and ±315° respectively. This result is consistent with the geometric phase principle and provides the necessary phase gradient for the generation of terahertz vortex beams.

[0066] like Figure 8As shown, the simulation results of the near-field reflection amplitude and reflection phase of the vortex beam generated under the condition of terahertz circularly polarized light incidence are shown. The two figures on the left are the simulation results of the near-field reflection amplitude and reflection phase of the vortex beam generated under the condition of left-handed circularly polarized wave incidence by dumbbell-shaped units with different rotation angles, and the two figures on the right are the simulation results of the near-field reflection amplitude and reflection phase of the vortex beam generated under the condition of right-handed circularly polarized wave incidence by dumbbell-shaped units with different rotation angles. The amplitude distribution diagram shows relatively uniform characteristics, and a dark ring is formed in the central area. This phenomenon confirms the existence of a phase singularity at the origin of the vortex beam. The phase singularity of the beam remains stable throughout the propagation process, while the field intensity of the outer ring is relatively large, forming a distribution morphology similar to a "donut". The generated vortex beam shows the number of phase singularities corresponding to the absolute value of the topological charge.

[0067] like Fig. 9 As shown in the figure, the simulation results of the far-field reflection amplitude and reflection phase of the vortex beam generated under the condition of terahertz circularly polarized light incidence are shown. The two figures on the left are the simulation results of the far-field reflection amplitude and reflection phase of the vortex beam generated by the dumbbell-shaped unit with different rotation angles under the condition of left-handed circularly polarized wave incidence, and the two figures on the right are the simulation results of the far-field reflection amplitude and reflection phase of the vortex beam generated by the dumbbell-shaped unit with different rotation angles under the condition of right-handed circularly polarized wave incidence. The generated vortex beams all show the characteristics of vortex beam column symmetry, and realize the continuous wavefront phase corresponding to the topological charge of the terahertz vortex phase plate, that is, the phase change of 0 to 6π.

[0068] The above is a detailed introduction to a terahertz vortex phase plate based on a dumbbell-shaped metasurface provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0069] In this article, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprising a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

Claims

1. A terahertz vortex phase plate based on a dumbbell-shaped metasurface, characterized in that: Comprising: a plurality of metasurface units arranged in the same plane; wherein: The metasurface unit comprises: a top basic unit metal structure layer, an intermediate dielectric layer and a base metal reflective surface layer; the top basic unit metal structure layer is a dumbbell-shaped structure, and its area is smaller than that of the intermediate dielectric layer and the base metal reflective surface layer; The positions of each layer of the multiple metasurface units are arranged correspondingly, and the phase distribution of the multiple top-level basic unit metal structure layers on the plane after arrangement satisfies the vortex beam phase distribution, forming a metasurface array with a target topological charge number; the metasurface array is a terahertz wave incident surface.

2. A terahertz vortex phase plate based on a dumbbell-shaped metasurface according to claim 1, characterized in that: Based on the finite element method, combined with the target relationship between the phase distribution required by the unit position (x, y) of the top basic unit metal structure layer in the metasurface array and the azimuth angle around the center point of the metasurface array, it is calculated that the phase distribution of the top basic unit metal structure layer in the metasurface array satisfies the vortex beam phase distribution formula: in, is the phase that the top basic unit metal structure layer needs to satisfy at the unit position (x, y) of the metasurface array, and l is the topological charge number.

3. The terahertz vortex phase plate based on dumbbell-shaped metasurface according to claim 1, characterized in that: The dumbbell-shaped structure includes: two semicircular structures and a rectangular structure; the diameter sides of the two semicircular structures are opposite and respectively connected to the two short sides of the rectangular structure, and the central axis of the rectangular structure passes through the center of the two semicircular structures to form an integrated dumbbell-shaped structure.

4. The terahertz vortex phase plate based on dumbbell-shaped metasurface according to claim 3, characterized in that: The radius of the semicircular structure is 37 μm, the short side of the rectangle is 25 μm, and the long side of the rectangle is 27 μm.

5. The terahertz vortex phase plate based on dumbbell-shaped metasurface according to claim 4, characterized in that: The intermediate dielectric layer is square, and the side length is 100 μm.

6. A terahertz vortex phase plate based on a dumbbell-shaped metasurface according to claim 3, 4 or 5, characterized in that: The base metal reflective surface layer is a square, and the side length thereof is equal to the side length of the intermediate dielectric layer.

7. The terahertz vortex phase plate based on dumbbell-shaped metasurface according to claim 3, characterized in that: The thickness of the top basic unit metal structure layer is 1 μm, the thickness of the intermediate dielectric layer is 25 μm, and the thickness of the base metal reflective surface layer is 1 μm.

8. The terahertz vortex phase plate based on dumbbell-shaped metasurface according to claim 1, characterized in that: The material of the top basic unit metal structure layer is metal copper.

9. The terahertz vortex phase plate based on dumbbell-shaped metasurface according to claim 1, characterized in that: The material of the intermediate dielectric layer is polyimide.

10. The terahertz vortex phase plate based on dumbbell-shaped metasurface according to claim 1, characterized in that: The material of the base metal reflective surface layer is metal copper.

Images