An I loop square core ultra-wideband terahertz mode demultiplexer and an implementation method thereof

Abstract

The application discloses an I-ring square-core ultra-wideband terahertz mode demultiplexer and an implementation method thereof, and belongs to the technical fields of terahertz technology and electromagnetic functional device technology. The demultiplexer comprises a multilayer structure formed by alternately stacking three layers of metal patterns and two layers of polyimide dielectric layers, and the multilayer structure constitutes a Fabry-Perot cavity; in the three layers of metal patterns, the upper layer and the lower layer are both one-dimensional metal gratings, and the extension directions of the two layers of gratings are orthogonal to each other; the metal pattern of the middle layer is an I-ring square-core metal structure formed by superimposing an I-shaped open ring and a central square; and the demultiplexer is formed into a metasurface array by arranging a plurality of functional units along a plane in a periodical mode. The demultiplexer has the advantages of simple structure, convenient preparation, certain deformation adaptation capability and process fault tolerance, low mode crosstalk, strong frequency adaptability, and the like, effectively improves the transmission capacity and working stability of a terahertz communication system, and is suitable for a terahertz high-speed multiplexing communication scene.

Description

Technical Field

[0001] This invention relates to the fields of terahertz technology and electromagnetic functional devices, and in particular to an I-ring square core ultrawideband terahertz mode demultiplexer and its implementation method. Background Technology

[0002] As communication technologies iterate towards higher speeds and larger capacities, sixth-generation mobile communication technology has become the core driving force for leaps in the communication field. The performance of the communication carrier directly determines the capacity and speed limits of the communication system. The terahertz wave band, located between microwaves and infrared light waves, possesses unique advantages such as low photon energy, high penetration, and wide bandwidth, making it one of the core carriers for ultra-high-speed communication. It can be widely used in fields such as security inspection, medical testing, and astronomy, and provides an important technological path to overcome existing communication speed bottlenecks. In the field of terahertz communication, multiplexing technology is a core means to improve channel transmission efficiency. Among them, optical orbital angular momentum multiplexing technology has received widespread attention in high-speed optical communication and quantum communication due to its unique spatial orthogonality. A beam carrying OAM has a helical phase structure. exp ( ilθ The topological charge l can take any integer value. The OAM modes corresponding to different topological charges are orthogonal to each other and do not interfere with each other. They can be used as independent communication channels to carry different data. Theoretically, they can provide an infinite number of channels, which can greatly improve the capacity of the communication system. It is one of the core technologies for realizing terahertz high-speed communication.

[0003] In practical applications of OAM multiplexing technology, mode multiplexers / demultiplexers, characterized by low insertion loss and high isolation, while achieving miniaturization and functional integration, are core components for building high-speed data transmission systems. In recent years, metasurfaces, with their ability to flexibly control the amplitude, phase, and polarization of light waves at subwavelength scales, as well as their planar shape and ease of integration, have shown great application potential in promoting the miniaturization and integration of space OAM communication systems. A metasurface is an artificially designed periodic structure composed of resonant units, capable of precisely controlling electromagnetic waves at subwavelength scales.

[0004] However, the number of existing terahertz OAM mode multiplexers / demultiplexers is small, and almost all of them are designed for a single specific frequency or a narrow bandwidth. Their operating bandwidth is generally less than 0.1THz, which cannot make full use of the extremely wide spectrum resources of the terahertz band, make it difficult to give full play to the channel expansion advantages of OAM multiplexing technology, and make it unable to meet the application requirements of ultra-high transmission rate and large transmission capacity. At the same time, existing demultiplexers have poor adaptability to carrier frequency drift. Frequency changes will cause fluctuations in the demultiplexer's operating efficiency, increase mode crosstalk, and insufficient anti-interference ability, which restricts the overall communication efficiency and reliability of terahertz communication systems.

[0005] Currently, the core problem hindering the development of terahertz mode demultiplexers towards ultra-wideband is the lack of a unit structure that can simultaneously satisfy both broadband operation and phase constant full coverage. This results in the phase compensation of conventional metasurfaces having strong frequency dependence, making it impossible to simultaneously achieve broadband operation and low mode crosstalk. Summary of the Invention

[0006] The purpose of this invention is to provide an I-ring square core ultrawideband terahertz mode demultiplexer and its implementation method to solve the above-mentioned technical problems.

[0007] To achieve the above objectives, the present invention provides an I-ring square-core ultrawideband terahertz mode demultiplexer and its implementation method, comprising a multilayer structure formed by alternating stacking of three metal patterns and two polyimide dielectric layers, wherein the multilayer structure constitutes a Fabry-Perot cavity; in the three metal patterns, the upper and lower layers are both one-dimensional metal gratings, and the extension directions of the two gratings are orthogonal to each other; the middle metal pattern is an I-ring square-core metal structure consisting of an I-shaped open ring and a central square superimposed. The demultiplexer consists of a metasurface array formed by arranging multiple functional units periodically along a plane, and eight functional units are obtained by adjusting the structural parameters of the intermediate layer.

[0008] Preferably, the axis of symmetry of the intermediate metal pattern is placed at a 45° angle to the x-axis; the structural parameters of the intermediate metal pattern include the outer radius, ring width, rotation angle, opening angle, and side length of the central square.

[0009] Preferably, the metal pattern is made of gold, the thickness of a single layer of the metal pattern is 0.2 μm, and the electrical conductivity is 4.561 × 10⁻⁶. 7 S / m; the dielectric constant of the polyimide dielectric layer is ε=3.5+0.01i, and the thickness of the single-layer dielectric layer is 40μm.

[0010] Preferably, the grating constant of the one-dimensional metal grating is 20 μm, and the width of a single metal rod is 8 μm.

[0011] Preferably, the periodic dimension of the functional unit is 110 μm, and the total thickness of a single functional unit is 80 μm.

[0012] Preferably, eight functional units with a phase spacing of π / 4 are obtained after phase discretization; the demultiplexer is composed of 60×60 functional units arranged periodically, and the eight functional units transmit with constant phase in the 0.34~1.47THz frequency band.

[0013] Preferably, the demultiplexer has a bidirectional mode conversion function. After the incident Gaussian beam passes through the demultiplexer, it generates vortex beams with four topological charges, which propagate obliquely along the +x, -x, +y, and -y axes, respectively, to achieve mode multiplexing. After the incident vortex beams with corresponding topological charges pass through the demultiplexer, they are focused at the corresponding axis to form Gaussian beams, thus achieving mode demultiplexing.

[0014] Preferably, the polyimide is a flexible dielectric layer; the functional unit has the ability to accommodate alignment errors.

[0015] A method for implementing an I-ring square-core ultrawideband terahertz mode demultiplexer includes the following steps: S1. Unit structure design: Construct a sandwich multilayer structure with three layers of metal patterns and two layers of polyimide dielectric layers stacked alternately to form a Fabry-Perot cavity; Set the middle metal layer as an I-shaped open ring with a square core metal structure superimposed on the center of the I-shaped open ring, Adjust the geometric parameters of the middle layer and optimize through simulation to obtain 8 functional units with a phase interval of π / 4, so as to achieve full phase range coverage from 0 to 2π. S2. Phase distribution calculation: Combining vortex phase, focusing phase and deflection phase, calculate the wavefront phase distribution corresponding to the four-channel orbital angular momentum mode and generate the phase arrangement diagram of the metasurface. S3. Demultiplexer array arrangement: The functional units are periodically arranged according to the phase arrangement diagram to form a metasurface array, thus obtaining a terahertz mode demultiplexer. S4. Performance Verification: Based on the Rayleigh-Sommerfeld diffraction integral algorithm, using a frequency interval of 0.1 THz, the entire operating frequency band from 0.34 to 1.47 THz is traversed, and frequency-by-frequency construction is performed. l The incident and outgoing light fields of vortex beams with four topological charges of ±1 and ±2 were calculated to obtain the mode demultiplexing and focusing performance data of the demultiplexer.

[0016] Preferably, in S2, the phase arrangement diagram is automatically generated using Python software.

[0017] Therefore, the present invention employs the above-mentioned I-ring square core ultrawideband terahertz mode demultiplexer and its implementation method, which has the following beneficial effects: 1. Ultra-wide operating bandwidth: This invention constructs a Fabry-Perot resonant cavity based on a sandwich structure of three metal layers and two dielectric layers, combined with the intermediate layer functional structure of the I-ring square core, achieving a 3dB operating bandwidth of 0.34~1.47THz, which is far superior to the bandwidth of existing demultiplexers of less than 0.1THz. It can make full use of the wide terahertz spectrum resources and adapt to the application requirements of high-speed and high-capacity communication.

[0018] 2. Highly efficient and stable phase control: By adjusting the intermediate layer structure parameters, eight functional units with a phase spacing of π / 4 can be obtained, achieving full-range phase coverage from 0 to 2π. Moreover, the transmission amplitude of each functional unit is approximately consistent across a wide frequency band, and the transmission phase remains constant. The frequency correlation of phase compensation is low, which fundamentally ensures the accuracy of mode demultiplexing and low crosstalk characteristics under broadband operation.

[0019] 3. Two-way multiplexing / demultiplexing integrated function: This demultiplexer can simultaneously realize OAM mode multiplexing and demultiplexing functions. A forward-incident Gaussian beam can generate four tilted vortex beams with different topological charges. A reverse-incident vortex beam can be restored to a Gaussian beam and focused in a specific direction. It has a high degree of functional integration and can be directly adapted to the two-way transmission requirements of terahertz communication systems.

[0020] 4. Excellent process and working condition adaptability: The demultiplexer adopts a polyimide flexible dielectric layer, which has a certain deformation working capability and can be adapted to complex application scenarios with bending and slight deformation; at the same time, the unit structure has the tolerance for manufacturing alignment error, which reduces the processing accuracy requirements, is suitable for mass industrial production, and can effectively reduce manufacturing costs.

[0021] Significantly improves communication system performance: This invention can achieve l The independent transmission and demultiplexing of ±1 and ±2 four-channel OAM signals, with low inter-channel crosstalk and stable focusing performance across the entire frequency band, can significantly improve the transmission capacity and operational reliability of terahertz communication systems, providing core demultiplexer support for next-generation terahertz multiplexed communication technology.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of an I-ring square core ultrawideband terahertz mode demultiplexer according to the present invention; Figure 2 This is a schematic diagram of the functional unit structure of the present invention, wherein (a) is a schematic diagram of the upper metal grating, (b) is a schematic diagram of the middle metal structure, and (c) is a schematic diagram of the lower metal grating. Figure 3 This is a top view of the intermediate layer structure of the eight functional units of the present invention; Figure 4 The graph shows the cross-polarization transmittance of the eight functional units of the present invention as a function of frequency. Figure 5 The graph shows the phase difference between the eight functional units of the present invention and functional unit 1 as a function of frequency. Figure 6 This is a schematic diagram of the phase distribution of the mode demultiplexing metasurface of the present invention; Figure 7 The diagram shows the incident and exit light field distributions for the four types of topologically charged vortex light incident according to the present invention. Figure 8 The figures show the cross-sectional intensity spectra of the four modes after demultiplexing at different frequencies according to the present invention, where (a) is... l The cross-sectional intensity spectrum at =+1, (b) is l The cross-sectional intensity spectrum at =-1, (c) is l The cross-sectional intensity spectrum at =+2, (d) is l Cross-sectional intensity spectrum at =-2; Figure 9 This is a comparison curve of the theoretical focal length and the calculated focal length across the entire frequency band of this invention. Attached Figure Description

[0024] 1. Metal grating; 2. PI dielectric layer; 3. I-ring square core metal structure. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0026] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or device.

[0027] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] like Figures 1-9 As shown, this invention provides an I-ring square-core ultra-wideband terahertz mode demultiplexer and its implementation method. The overall structure of the I-ring square-core ultra-wideband terahertz mode demultiplexer, from top to bottom, consists of a metal grating 1, a PI dielectric 2, an I-ring square-core metal structure 3, a PI dielectric 2, and the metal grating 1. The specific structure of the basic unit of the demultiplexer is as follows: The I-ring square-core ultrawideband terahertz OAM mode demultiplexer adopts a sandwich multilayer structure with alternating layers of three metal patterns and two polyimide (PI) dielectric layers. These multiple layers together form a Fabry-Perot resonant cavity, improving overall transmission efficiency by suppressing reflection loss. Combined with... Figure 2 As shown, Figure 2 This is a schematic diagram of the layered unit structure, where Figure 2 (a) is a schematic diagram of the upper metal pattern. Figure 2 (b) is a schematic diagram of the intermediate layer metal pattern. Figure 2 (c) is a schematic diagram of the lower metal pattern. All three metal patterns are made of gold (Au), with a single layer thickness of 0.2 μm and an electrical conductivity of 4.561 × 10⁻⁶. 7 S / m. Two PI dielectric layers 2 fill the spaces between adjacent metal patterns. Each PI dielectric layer 2 has a thickness of 40 μm and a dielectric constant of ε = 3.5 + 0.01i. The total thickness of a single functional unit is approximately 80 μm, which is approximately equal to 0.2λ at a center frequency of 0.9 THz. The unit period size is set to 110 μm. Both the upper and lower metal patterns are one-dimensional metal grating 1 structures. The extension directions of the two gratings are orthogonal to each other, forming a polarization selection structure. The grating constant is 20 μm, and the width of a single metal rod is 8 μm. The top and bottom gratings serve as polarization selectors at the incident and exit ends, respectively, allowing only terahertz waves with specific polarization directions to pass through. The intermediate metal pattern serves as a functional control layer, employing an I-shaped open ring with a square core metal structure 3 superimposed on the center. The overall symmetry axis is positioned at a 45° angle to the x-axis, enabling cross-polarization conversion and precise phase control of the incident terahertz wave. The adjustable structural parameters of this intermediate layer include the outer radius of the I-shaped open ring. r Ring width w Rotation angle α Zhang Jiao β And the side length of the centrally superimposed squares. n .

[0029] This unit structure is based on the resonance principle of Fabry-Perot cavity. Electromagnetic waves undergo multiple reflections and transmissions within the multi-layer structure. The resonance enhancement effect improves the cross-polarization transmittance while suppressing reflection loss, ensuring the high transmission efficiency of the demultiplexer in a wide frequency band.

[0030] To achieve phase modulation across the entire range of 0 to 2π, this embodiment adjusts the geometric parameters (outer radius) of the intermediate layer metal pattern. r Ring width w Rotation angle α Zhang Jiao β、 Side length of the square n), and used electromagnetic simulation software to perform parameter scanning and optimization, and performed phase discretization processing from a large number of candidate structures, finally obtaining 8 functional units. The top view of the intermediate layer of the 8 functional units is as follows. Figure 3 As shown. The phase difference between adjacent units of the eight functional units (hereinafter referred to as units) is π / 4, collectively covering the full phase range of 0~2π. Simultaneously, the cross-polarization transmission amplitudes of the eight functional units are approximately consistent, ensuring the overall uniformity of the optical field intensity of the demultiplexer. Combined with... Figure 4 and Figure 5 The broadband characteristics of the unit are explained. Figure 4 Simulated curves showing the cross-polarization transmittance as a function of frequency for eight functional units are presented, with the horizontal axis representing frequency (in THz) and the vertical axis representing cross-polarization transmittance. Figure 4 It can be seen that within the wide frequency band of 0.34~1.47THz, the cross-polarization transmittance of the eight functional units remains at around 0.9, with only a small fluctuation of about 10%, demonstrating high and stable transmission efficiency. Figure 5 The graph shows the phase difference between the eight functional units and unit 1 as a function of frequency. The horizontal axis represents frequency (THz), and the vertical axis represents phase difference (°). Figure 5 It can be seen that in the 0.34~1.47THz frequency band, the phase difference curves of each unit are approximately parallel straight lines, the phase difference between adjacent units is stably maintained at about π / 4 (45°), the transmission phase fluctuates very little with frequency, and it has the characteristic of broadband constant phase, which provides a core foundation for building a broadband metasurface demultiplexer.

[0031] The aforementioned characteristics address the strong frequency correlation defect of conventional metasurface phase compensation, enabling the demultiplexer built based on this unit to maintain stable wavefront modulation capability over a wide frequency band, while achieving broadband operation and low mode crosstalk.

[0032] Regarding the overall array and phase distribution of the demultiplexer, in this embodiment, the terahertz mode demultiplexer is composed of the above-mentioned 8 functional units arranged periodically, forming a 60×60 functional unit array. To achieve the four-channel OAM mode demultiplexing function, a corresponding wavefront phase distribution needs to be designed for the metasurface array. The phase distribution needs to simultaneously superimpose three phase components: vortex phase, focusing phase, and deflection phase. Vortex phase: used to match vortex beams with different topological charges to achieve orthogonal separation of modes; focusing phase: used to focus the demultiplexed Gaussian beam to improve the power density at the receiver; deflection phase: used to deflect the beams of different channels in different directions to achieve spatial channel separation.

[0033] This invention is designed to support l =+1、 l =-1、 l =+2、 lThe OAM modes of four topological loads (=-2) correspond to four independent channels, propagating at inclinations along the +x, -x, +y, and -y axes, respectively. The phase arrangement of the metasurface is automatically calculated and generated using Python programming. The final demultiplexed metasurface phase distribution is shown below. Figure 6 As shown.

[0034] The demultiplexer of this invention has a bidirectional mode conversion function, which can simultaneously realize OAM mode multiplexing and OAM mode demultiplexing. The specific working process is as follows: OAM mode multiplexing function: When an x-polarized Gaussian beam is incident perpendicularly along the z-axis, the beam is converted into four y-polarized vortex beams after phase modulation by the metasurface. Each of the four beams carries... l =+1、 l =-1、 l =+2、 l The topological charge is -2, and it propagates at an angle along the four axes of +x, -x, +y, and -y, respectively, thereby realizing mode multiplexing from one Gaussian light to four OAM signals.

[0035] OAM mode demultiplexing function: When separately injected carrying l =+1、 l =-1、 l =+2、 l When a vortex beam with a topological charge of -2 is applied, the vortex beam with the corresponding topological charge is restored to a Gaussian beam after phase compensation by the metasurface, and is deflected and focused along the corresponding axis. Beams without the corresponding topological charge cannot achieve phase matching and will not form a focused spot at the corresponding position. The channels of different OAM modes are independent of each other, which can effectively suppress crosstalk between channels.

[0036] Combination Figure 7 The demultiplexing effect is explained. Figure 7 for l =+1、 l =-1、 l =+2、 l =-2 The light field intensity distribution diagrams of the incident and output fields when four types of vortex beams are incident respectively. Taking a center frequency of 0.9THz as an example, the incident vortex beam has a ring-shaped intensity distribution. After passing through the demultiplexer, the output beam forms a Gaussian-like focused spot on the focal plane of the corresponding axis. This verifies that the demultiplexer can restore the higher-order OAM mode to the fundamental mode Gaussian beam, achieving accurate mode demultiplexing.

[0037] To verify the demultiplexer's performance across the entire frequency band from 0.34 to 1.47 THz, this embodiment utilizes the Rayleigh-Sommerfeld diffraction integral algorithm and employs Python programming to automate the full-band optical field calculation and performance verification. The specific verification process is as follows: Multiple frequency points were selected within the operating frequency band of 0.34–1.47 THz, with a frequency interval of 0.1 THz; for each frequency point, a separate system was constructed. l =+1、 l =-1、 l =+2、 l =-2 Vortex incident field of four topological charges; Based on the phase modulation characteristics of metasurface, the output light field distribution at each frequency point is calculated, and the intensity distribution of the x=0 and y=0 sections is extracted to plot the mode intensity spectrum.

[0038] Spectral results at different frequencies are as follows Figure 8 As shown, including l =±1、 l The intensity distribution of the four modes (±2) at the x=0 and y=0 sections. Figure 8 It can be seen that within a wide frequency range from 0.4THz to 1.4THz, the emitted light of all four modes can form a clear Gaussian focused spot at the designed position. The position and intensity of the spot fluctuate little with frequency, proving that the demultiplexer can stably achieve efficient conversion between terahertz high-order OAM mode and fundamental mode in the entire operating frequency range, and the accuracy and consistency of mode demultiplexing are good.

[0039] Furthermore, the focusing performance across the entire frequency band was verified: the actual focal length calculated frequency-by-frequency was compared with the theoretically designed focal length, and the comparison curve is shown below. Figure 9 As shown, the horizontal axis represents frequency (unit: THz), and the vertical axis represents focal length (unit: mm). Figure 9 It can be seen that within the wide frequency band of 0.34~1.47THz, the calculated focal length obtained based on the Rayleigh-Sommerfeld diffraction algorithm has a high degree of consistency with the theoretical focal length, and the error between the two is small, proving that the demultiplexer has stable focusing performance and strong frequency adaptability within the wide frequency band.

[0040] In summary, the demultiplexer of this invention can be fabricated using conventional micro-nano fabrication processes, and its multi-layer structure can be fabricated through processes such as photolithography, metal evaporation, and spin coating of dielectric layers. Because the demultiplexer uses a flexible PI dielectric layer, it possesses a certain degree of deformation capability, adapting to applications involving bending and slight deformation, thus expanding the applicable conditions of the demultiplexer. Simultaneously, the metasurface unit structure of this invention has a certain tolerance for alignment errors during the fabrication process, reducing the requirements for processing precision, making it suitable for mass industrial production, effectively reducing the manufacturing cost of the demultiplexer, and enhancing its potential for engineering applications.

[0041] This invention also provides a method for implementing an I-ring square-core ultra-wideband terahertz OAM mode demultiplexer, specifically including the following steps: S1. Unit Structure Design: A sandwich multilayer structure consisting of three metal patterns and two PI dielectric layers is constructed to form a Fabry-Perot resonant cavity. The middle metal layer is designed as an I-shaped open ring with a square superimposed on the center, and the whole structure is placed at a 45° angle to the x-axis. By adjusting the geometric parameters of the middle layer (outer radius, ring width, rotation angle, opening angle, and square side length), and combining electromagnetic simulation software for parameter optimization and phase discretization, eight functional units with approximately the same transmission amplitude and an adjacent phase difference of π / 4 are finally obtained, achieving full phase coverage from 0 to 2π, and the unit maintains stable transmission phase in the 0.34 to 1.47 THz frequency band.

[0042] S2, Phase Distribution Calculation: (For...) l =±1、 l The functional requirement of ±2 four-channel OAM mode demultiplexing is met. Combining three phase components—vortex phase, focusing phase, and deflection phase—the wavefront phase distribution required for the metasurface is calculated. The phase layout diagram adapted to the 60×60 array size is automatically generated through Python programming to complete the phase mapping of each position in the array.

[0043] S3. Demultiplexer array arrangement: According to the generated phase arrangement diagram, the eight functional units are matched with the phase requirements of each position in the array and then periodically arranged to form a 60×60 metasurface array, thus obtaining the terahertz mode demultiplexer.

[0044] S4. Broadband Performance Verification: Based on the Rayleigh-Sommerfeld diffraction integral algorithm, the entire operating frequency band from 0.34 to 1.47 THz is traversed at set frequency intervals to construct frequency-by-frequency... l =±1、 l The incident and outgoing light fields of vortex light with four topological charges were calculated. The accuracy of mode demultiplexing, mode conversion consistency and focusing stability of the demultiplexer were verified by analyzing the cross-sectional intensity distribution and focal length deviation.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A square-core I-ring ultrawideband terahertz mode demultiplexer, characterized in that: It includes a multi-layered structure formed by alternating stacking of three layers of metal patterns and two layers of polyimide dielectric layers, which constitutes a Fabry-Perot cavity; In the three-layer metal pattern, the upper and lower layers are both one-dimensional metal gratings, and the extension directions of the two gratings are orthogonal to each other; the middle layer metal pattern is an I-shaped open ring and a central square superimposed I-shaped square core metal structure. The demultiplexer is a metasurface array formed by arranging multiple functional units periodically along a plane.

2. The I-ring square core ultrawideband terahertz mode demultiplexer according to claim 1, characterized in that: The axis of symmetry of the intermediate metal pattern is placed at a 45° angle to the x-axis; the structural parameters of the intermediate metal pattern include the outer radius, ring width, rotation angle, opening angle, and side length of the central square.

3. The I-ring square core ultrawideband terahertz mode demultiplexer according to claim 1, characterized in that: The metal pattern is made of gold, with a single layer thickness of 0.2 μm and an electrical conductivity of 4.561 × 10⁻⁶. 7 S / m; the dielectric constant of the polyimide dielectric layer is ε=3.5+0.01i, and the thickness of the single-layer dielectric layer is 40μm.

4. The I-ring square core ultrawideband terahertz mode demultiplexer according to claim 1, characterized in that: The grating constant of the one-dimensional metal grating is 20 μm, and the width of a single metal rod is 8 μm.

5. The I-ring square-core ultrawideband terahertz mode demultiplexer according to claim 1, characterized in that: The periodic dimension of the functional unit is 110 μm, and the total thickness of a single functional unit is 80 μm.

6. The I-ring square-core ultrawideband terahertz mode demultiplexer according to claim 1, characterized in that: Eight functional units with a phase spacing of π / 4 were obtained after phase discretization. The demultiplexer consists of 60×60 functional units arranged periodically, and the eight functional units transmit with constant phase in the 0.34~1.47THz frequency band.

7. The I-ring square-core ultrawideband terahertz mode demultiplexer according to claim 1, characterized in that: The demultiplexer has a bidirectional mode conversion function. After the incident Gaussian beam passes through the demultiplexer, it generates vortex beams with four topological charges, which propagate at an angle along the +x, -x, +y, and -y axes, respectively, to achieve mode multiplexing. After the incident vortex beams with corresponding topological charges pass through the demultiplexer, they are focused at the corresponding axis to form Gaussian beams, thus achieving mode demultiplexing.

8. The I-ring square core ultrawideband terahertz mode demultiplexer according to claim 1, characterized in that: Polyimide serves as a flexible dielectric layer; the functional units possess the capability to accommodate alignment errors.

9. A method for implementing an I-ring square-core ultra-wideband terahertz mode demultiplexer according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Unit structure design: Construct a sandwich multilayer structure with three layers of metal patterns and two layers of polyimide dielectric layers stacked alternately to form a Fabry-Perot cavity; The intermediate metal layer is set as an I-shaped open ring with a square I-shaped core metal structure superimposed on the center. By adjusting the geometric parameters of the intermediate layer and optimizing through simulation, eight functional units with a phase interval of π / 4 are obtained, achieving full phase range coverage from 0 to 2π. S2. Phase distribution calculation: Combining vortex phase, focusing phase and deflection phase, calculate the wavefront phase distribution corresponding to the four-channel orbital angular momentum mode and generate the phase arrangement diagram of the metasurface. S3. Demultiplexer array arrangement: The functional units are periodically arranged according to the phase arrangement diagram to form a metasurface array, thus obtaining a terahertz mode demultiplexer. S4. Performance Verification: Based on the Rayleigh-Sommerfeld diffraction integral algorithm, using a frequency interval of 0.1 THz, the entire operating frequency band from 0.34 to 1.47 THz is traversed, and frequency-by-frequency construction is performed. l The incident and outgoing light fields of vortex beams with four topological charges of ±1 and ±2 were calculated to obtain the mode demultiplexing and focusing performance data of the demultiplexer.

10. The implementation method of an I-ring square-core ultrawideband terahertz mode demultiplexer according to claim 9, characterized in that: In S2, the phase arrangement diagram is automatically generated using Python software.

Images