Terahertz orbital angular momentum mode router and construction method thereof

Abstract

The invention relates to the technical field of wireless communication, in particular to a terahertz orbital angular momentum mode routing device and a construction method thereof. Each layer of metasurface is composed of unit structures in two-dimensional distribution, and each unit structure of the metasurface comprises a grid structure, a dielectric plate and an antenna structure which are arranged in sequence; the grid structure and the antenna structure are respectively arranged on two sides of the dielectric layer; performing frequency domain finite element simulation by adjusting geometric parameters of the meta-structure surface unit structure to obtain an electromagnetic response curve covering [0-2pi]; according to target input and output orbital angular momentum mode field distribution, constructing phase distribution of a multi-stage phase modulation model; antenna structures are arranged according to the phase distribution and the electromagnetic response curve, and a multi-layer cascaded super-structure surface device is formed. And establishing a mapping relation of an orbital angular momentum mode group by utilizing a progressive regulation mechanism of a beam phase, and realizing terahertz routing communication application of a multiplexing orbital angular momentum mode.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and in particular, to a terahertz orbital angular momentum mode routing device and a construction method thereof. Background Art

[0002] As a bridge connecting the microwave and optical bands, terahertz has rich spectral resources, ultra-high data transmission rates, and an excellent connection experience, and is considered to be one of the key technologies driving the transformation of the next-generation mobile communication. The orbital angular momentum (OAM) mode, as an eigen-solution of the wave equation, has infinite orthogonality in the Hilbert space, can provide a new physical dimension, and can be used as a carrier of signals to multiply the communication capacity and spectral efficiency.

[0003] At present, the orthogonal frequency division multiplexing technology can effectively resist the multipath effect and improve the spectral utilization rate. However, the limited spectral resources are still difficult to meet the exponentially growing communication service demands, and it is urgent to find new spectral resources and physical dimensions to break through this bottleneck. There are problems such as single function and low energy utilization rate in the regulation of existing terahertz OAM mode communication. The development of frontier applications such as smart cities, smart transportation, and intelligent manufacturing has put forward new demands on the mobile communication network in terms of communication capacity and spectral efficiency. How to perform efficient selective routing on the terahertz band OAM mode, thereby increasing the number of multiplexed channels and reducing the bit error rate, is a key problem that needs to be solved urgently.

[0004] The above content is only used to assist in understanding the technical solution of the present invention, and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main objective of the present invention is to provide a terahertz orbital angular momentum mode routing device and a construction method thereof, aiming to solve the technical problems of single function and low energy utilization rate existing in the prior art when using a grid and a spiral phase plate for mode conversion and separation.

[0006] To achieve the above objective, the present invention proposes a terahertz orbital angular momentum mode routing device, and the terahertz orbital angular momentum mode routing device includes: a multi-level cascaded metasurface device;

[0007] Each of the metasurface devices includes: a two-dimensional planar distributed metasurface unit structure;

[0008] The metasurface unit structure includes: a grid structure, a dielectric plate, and an antenna structure arranged in sequence;

[0009] The grid structure and the antenna structure are respectively arranged on two sides of the dielectric layer;

[0010] By adjusting the geometric parameters of the metasurface unit structure, finite element simulation in the frequency domain is carried out to obtain the electromagnetic response curve covering [0 - 2π];

[0011] Construct the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distributions;

[0012] Arrange the antenna structure according to the phase distribution and the electromagnetic response curve to form a multi-level cascaded metasurface device.

[0013] Optionally, the grid structure is made of a metal material such as copper or gold;

[0014] The grid structure is a rectangular metal with the same interval, and the interval matches the wavelength of the electromagnetic wave;

[0015] The grid structure is used to filter electromagnetic waves of a preset polarization and enhance the electromagnetic response.

[0016] Optionally, the antenna structure is made of a metal material such as copper or gold;

[0017] The shape and geometric parameters of the antenna structure are set according to the electromagnetic response curve;

[0018] The antenna structure is used for polarization conversion and superimposing a specific phase delay.

[0019] Optionally, the material of the dielectric plate is selected as resin glass with a low dielectric constant and loss coefficient;

[0020] By adjusting the dielectric thickness of the dielectric plate, the thickness of the grid structure, and the thickness of the antenna structure, a preset terahertz frequency band is obtained.

[0021] In addition, to achieve the above object, the present invention also provides a method for constructing a routing device. The method for constructing a routing device is used to construct the terahertz orbital angular momentum mode routing device as described above. The steps of the method for constructing a routing device include:

[0022] Design the metasurface unit structure according to the electromagnetic response curve covering [0 - 2π];

[0023] Construct a multi-level phase model and design the target input and output orbital angular momentum mode field distributions;

[0024] Obtain the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distributions;

[0025] Arrange the metasurface antennas according to the phase distribution and the electromagnetic response curve to form a multi-level cascaded metasurface device.

[0026] Optionally, the steps of constructing the multi-level phase model and designing the target input and output orbital angular momentum mode field distributions include:

[0027] Construct a Laguerre-Gaussian mode as a mathematical expression model of the input electromagnetic field distribution;

[0028] Set the beam radial index in the Laguerre-Gaussian mode to 0, and use different angular indices to obtain the corresponding angular momentum mode field distributions.

[0029] Optionally, the steps of setting the beam radial index in the Laguerre-Gaussian mode to 0 and using different angular indices to obtain the corresponding angular momentum mode field distributions include:

[0030] Set the beam radial index in the Laguerre-Gaussian mode to 0, and use different angular indices to obtain the corresponding angular momentum modes;

[0031] Use the electromagnetic field distribution at the center to form the target input field distribution;

[0032] Use the electromagnetic field distribution at the center to superimpose the gradient phase distribution to guide the transmission direction of the output electromagnetic field to form the target output field distribution.

[0033] Optionally, the steps of obtaining the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distributions include:

[0034] Construct a mathematical model of progressive modulation of multiple phase planes;

[0035] Set the objective function of the progressive modulation mathematical model, and solve the phase distribution that satisfies the target input and output orbital angular momentum mode field distributions according to the gradient descent algorithm.

[0036] Optionally, after the steps of obtaining the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distributions, it further includes:

[0037] Use the complex mean square error distribution as the error function between the target input and output orbital angular momentum mode field distributions and the actual field distribution;

[0038] Use adaptive moment estimation optimization to obtain the target input and output orbital angular momentum mode field distributions where the loss function converges to the target loss value.

[0039] Optionally, the steps of arranging the metasurface antennas according to the phase distribution and the electromagnetic response curve to form a multi-level cascaded metasurface device include:

[0040] Arrange the metasurface antennas according to the phase distribution and the electromagnetic response curve;

[0041] Rotate the direction of the grating structure in the even layers according to the polarization mode, construct the metasurface unit structure on the dielectric plate, and form a multi-layer cascaded metasurface device according to the phase distribution.

[0042] The present invention provides a terahertz orbital angular momentum mode routing device and a construction method thereof. The terahertz orbital angular momentum mode routing device includes: a multi-layer cascaded metasurface device; each layer of the metasurface is composed of a two-dimensional distributed unit structure, and each of the metasurface unit structures includes: a grating structure, a dielectric plate, and an antenna structure arranged in sequence; the grating structure and the antenna structure are respectively arranged on two sides of the dielectric layer; by adjusting the geometric parameters of the metasurface unit structure, perform finite element simulation in the frequency domain to obtain an electromagnetic response curve covering [0-2π]; construct the phase distribution of a multi-stage phase modulation model according to the target input and output orbital angular momentum mode field distributions; arrange the antenna structure according to the phase distribution and the electromagnetic response curve to form a multi-layer cascaded metasurface device. By cascading multiple metasurface devices and using their progressive beam phase control mechanism, a complex mapping relationship of the orbital angular momentum mode group is established, and then the terahertz routing communication application of multiplexing orbital angular momentum modes is realized. Description of the Drawings

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0044] Figure 1 Schematic left view structure of the metasurface unit structure in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention;

[0045] Figure 2 Schematic side view structure of the metasurface unit structure in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention;

[0046] Figure 3 Top view of the single-layer metasurface device in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention;

[0047] Figure 4 Schematic diagram of the transmittance relationship between the S parameter and the frequency in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention;

[0048] Figure 5Schematic diagram of the phase and amplitude response curves of different geometric structures in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention;

[0049] Figure 6 Schematic flow chart of the first embodiment of the method for constructing the routing device of the present invention;

[0050] Figure 7 Schematic diagram of the structure with horizontally polarized incidence in the first embodiment of the method for constructing the routing device of the present invention;

[0051] Figure 8 Schematic diagram of the structure with vertically polarized incidence in the first embodiment of the method for constructing the routing device of the present invention;

[0052] Figure 9 Schematic flow chart of the second embodiment of the method for constructing the routing device of the present invention;

[0053] Figure 10 Schematic diagram of the structure of the second embodiment of the method for constructing the routing device of the present invention.

[0054] The realization, functional features and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings. Specific embodiments

[0055] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0057] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0058] In addition, the descriptions involving "first", "second", etc. in the present invention are for descriptive purposes only, and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments may be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0059] The main solution of the embodiment of the present invention is that: the terahertz orbital angular momentum mode routing device includes: a multi-level cascaded metasurface device; the metasurface device includes: a unit structure distributed in a two-dimensional plane; the metasurface unit structure includes: a grid structure, a dielectric plate, and an antenna structure arranged in sequence; the grid structure and the antenna structure are respectively arranged on two sides of the dielectric layer; by adjusting the geometric parameters of the metasurface unit structure, performing finite element simulation in the frequency domain, an electromagnetic response curve covering [0 - 2π] is obtained; a phase distribution of a multi-level phase modulation model is constructed according to the target input and output orbital angular momentum mode field distributions; the antenna structures are arranged according to the phase distribution and the electromagnetic response curve to form a multi-level cascaded metasurface device.

[0060] The existing modulation techniques for terahertz OAM modes mainly include two schemes: spiral phase plates and vortex gratings. By superimposing a spiral phase wavefront distribution on a plane wave, a spiral phase plate can change the spatial structure of the output beam and present a "doughnut"-shaped intensity distribution. However, this method can only generate a single OAM mode and cannot achieve the generation and conversion of multiple OAM modes. To generate multiple axially multiplexed OAM modes, a cascade of multiple beam splitters is required. This will greatly increase the system complexity and reduce the energy utilization rate. The Dammann vortex grating realizes the diffraction and conversion of OAM modes by superimposing a spiral phase distribution on the basis of the periodic grating phase and optimizing the energy distribution of each diffraction order. By superimposing the gradient phase and spiral transformation in different diffraction directions, the vortex grating phase can be obtained. This vortex grating phase can diffract the incident OAM mode beam and restore it to a Gaussian beam at a specific diffraction order. Although the grating modulation method can cover a large range of OAM modes, its energy equalization characteristic related to the number of diffractions results in low energy utilization rate and is difficult to be applied in large-scale terahertz communications. In a terahertz OAM mode channel, multiple cascaded devices are usually used to realize the multiplexing and demultiplexing of OAM mode groups. However, the fixed phase response makes the generation of modes require a cascade of multiple spiral phase diffraction plates and beam splitters, greatly increasing the complexity of the communication system. Therefore, how to optimize the design of diffraction devices to make them have high energy utilization rate and rich modulation functions is the key to promoting the practical application of high-capacity terahertz OAM mode communication.

[0061] This solution proposes a terahertz orbital angular momentum mode routing device for realizing the high-energy-utilization selective angular routing of OAM modes. By cascading multiple metasurface devices and using their progressive modulation mechanism for beam phase, a complex mapping relationship of the orbital angular momentum mode group is established, and then the terahertz routing communication application of multiplexed orbital angular momentum modes is realized. This device is composed of a cascade of multiple planar transmissive metasurface devices, and each planar device is composed of two-dimensional arranged antennas with different geometric characteristics.

[0062] Refer to Figure 1 and Figure 2 , Figure 1 is a left-view structural schematic diagram of the metasurface unit structure in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention, Figure 2 is a side-view structural schematic diagram of the metasurface unit structure in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention. As shown in Figure 1 , in this embodiment, the terahertz orbital angular momentum mode routing device includes: a cascade of multiple metasurface devices. At the same time, each of the metasurface devices includes: a two-dimensional planar distributed metasurface unit structure. Refer to Figure 3 , Figure 3This is a top view of the single-layer metasurface device in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention. The metasurface device is formed by arranging multiple unit structures in a two-dimensional plane.

[0063] Among them, the metasurface unit structure includes: a grid structure 10, a dielectric plate 20, and an antenna structure 30 arranged in sequence; the grid structure and the antenna structure are respectively arranged on two sides of the dielectric layer.

[0064] It should be noted that by adjusting the geometric parameters of the metasurface unit structure, frequency-domain finite element simulation can be carried out to obtain an electromagnetic response curve covering [0-2π]; the phase distribution of a multi-level phase modulation model is constructed according to the target input and output orbital angular momentum mode field distributions; the antenna structure is arranged according to the phase distribution and the electromagnetic response curve to form a multi-level cascaded metasurface device.

[0065] It should be understood that the dielectric material in the metasurface unit structure is generally resin glass, including but not limited to Rogers 5880, PTFE, or F4B, etc., which has a low dielectric constant and loss coefficient. The metal material is mainly copper or gold, distributed on both sides of the dielectric plate. Among them, one side is a grid structure, which is used to filter electromagnetic waves of a specific polarization and enhance the electromagnetic response. The grid is composed of rectangular metals with the same interval, and the interval should match the wavelength of the electromagnetic wave. The other side is an antenna structure, which is used for polarization conversion and superimposing a specific phase delay. The example given here is a "V-shaped" antenna structure. In addition, "circular" and "rectangular" antenna structures can also be selected. By changing the geometric parameters of the antenna, different electromagnetic phase and amplitude responses can be obtained. In the specific design process, the electromagnetic response of the metasurface unit is calculated by analyzing the S parameters of the electromagnetic field through frequency-domain finite element analysis, and the transmittance and phase delay responses in different polarization states are analyzed.

[0066] Refer to Figure 4 and Figure 5 , Figure 4 This is a schematic diagram of the relationship between the S parameter and the transmittance of frequency in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention, Figure 5 This is a schematic diagram of the phase and amplitude response curves of different geometric structures in the first embodiment of the terahertz orbital angular momentum mode routing device of the present invention. Figure 4 In it, Rxx represents the reflection coefficient of x-polarized input and x-polarized output, and Txx represents the transmission coefficient of x-polarized input and x-polarized output. The abscissa of the coordinate system is frequency (Frequency / THz), and the ordinate is the transmittance amplitude (Amplitude / dB). The analysis of the transmission coefficient shows that the amplitude transmittance of Tyx at the center frequency band of 0.24 THz is greater than -3 dB, while Txx is less than -8 dB, which means that the designed metasurface device has the polarization conversion function. Figure 5The phase and amplitude response curves of 16 different geometric structures (corresponding to Structure Num 1-16) are given. This structure can better cover the interval from 0 to 2π, and the transmittance of the unit structure is greater than 60%.

[0067] Furthermore, by changing the dielectric material, dielectric thickness, and metal layer thickness, other metasurface devices in the terahertz frequency band can be obtained. The processing technology of this metasurface unit device includes precision metal processing, 3D printing, etc.

[0068] In this embodiment, the terahertz orbital angular momentum mode routing device includes: a multi-level cascaded metasurface device; each of the metasurface devices includes: a two-dimensional planar distributed metasurface unit structure; the metasurface unit structure includes: a grid structure, a dielectric plate, and an antenna structure arranged in sequence; the grid structure and the antenna structure are respectively arranged on both sides of the dielectric layer; by adjusting the geometric parameters of the metasurface unit structure, frequency-domain finite element simulation is carried out to obtain an electromagnetic response curve covering [0-2π]; according to the target input and output orbital angular momentum mode field distributions, the phase distribution of a multi-level phase modulation model is constructed; according to the phase distribution and the electromagnetic response curve, the antenna structure is arranged to form a multi-level cascaded metasurface device. By cascading multiple metasurface devices and using their progressive beam phase control mechanism, a complex mapping relationship of the orbital angular momentum mode group is established, and then a terahertz routing communication application that multiplexes orbital angular momentum modes is realized.

[0069] In addition, to achieve the above object, the embodiment of the present invention also proposes a method for constructing a routing device. Since this method for constructing a routing device is used to construct the above-mentioned terahertz orbital angular momentum mode routing device, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated one by one here.

[0070] Refer to Figure 6 , Figure 6 which is a schematic flowchart of the first embodiment of the method for constructing a routing device of the present invention. As Figure 6 shown, in this embodiment, the content that is the same as or similar to the above embodiment can be referred to the above introduction and will not be elaborated later. The steps of the method for constructing a routing device include:

[0071] Step S10: Design a metasurface unit structure according to the electromagnetic response curve covering [0-2π].

[0072] It should be noted that the electromagnetic response curve can be adjusted by changing the interval of the grid structure, the geometric parameters of the antenna, and changing the dielectric material, dielectric thickness, and metal layer thickness.

[0073] Step S20: Construct a multi-level phase model and design the target input and output orbital angular momentum mode field distributions.

[0074] Step S30: Obtain the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distributions.

[0075] It should be noted that after obtaining the metaatoms with a phase coverage of 0 to 2π and high transmittance, a specific phase distribution needs to be designed to meet the corresponding regulation functions, and the metaatoms are arranged to obtain the metasurface device. Before this, we first analyze the electromagnetic field mathematical model of the input and output beams. Here, the Laguerre-Gaussian mode is selected as the mathematical expression model of the input electromagnetic field distribution, and its electric field distribution is as follows:

[0076]

[0077]

[0078] where (r,θ) are the components in the polar coordinate system, i 2 = -1, p and l respectively represent the radial and angular exponents of the beam, and z is the beam propagation distance. is the beam waist radius of the beam, w 0 is the beam waist radius of the fundamental mode Gaussian beam at z = 0, is the Rayleigh distance, is the Laguerre coefficient polynomial:

[0079]

[0080] Substituting the radial exponent p = 0 and different l into the electric field distribution formula, the corresponding OAM mode electric field distribution can be obtained. It should be noted that the Laguerre-Gaussian beam is the eigen-solution of the OAM mode, which can more accurately characterize the field distribution of the OAM mode and improve the accuracy of subsequent model training. If other electromagnetic field mathematical models of the OAM mode are used, the training error will be further superimposed, reducing the regulation accuracy of the model. The input end is composed of electromagnetic field distributions with different OAM modes and located at the center. The output end is superimposed with a gradient phase distribution on this basis to guide the transmission direction of the output electromagnetic field, and the output electromagnetic field distribution is:

[0081] E out (x,y,z) = E(r,θ,z) × exp(ikxsin(α) + ikysin(β))

[0082] Among them, \(k = 2\pi / \lambda\) is the spatial wave vector, and \(\alpha\) and \(\beta\) are the diffraction angles in the \(x\) and \(y\) directions, which are used to change the transmission direction of the beam. By setting different input OAM modes, output OAM modes and directions, an output-output electromagnetic field mapping group is established. However, a single-phase diffraction plane can only achieve diffraction in one direction and OAM mode, and cannot simultaneously respond to multiple different OAM modes and endow angular independent routing. Therefore, a multi-level phase modulation model using cascaded multiple phase planes is required to achieve this.

[0083] During the spatial transmission of the input electromagnetic field, it will be gradually modulated by multiple phase planes, thereby realizing the mapping of the input-output mode group. The mathematical model of its progressive modulation is as follows:

[0084]

[0085] Among them, \(H\) represents the scalar electromagnetic field diffraction matrix, \((f x ,f y )\) is the spatial frequency in the \((x,y)\) direction, and \(d z \) is the transmission distance.

[0086]

[0087] Among them, \(\varphi n \) is the \(n\)th layer phase diffraction matrix, and are the input and output electromagnetic field distributions respectively. Among them, \(\varphi n \) is the unknown parameter in this model. By setting the objective function and combining the gradient descent algorithm, the phase matrix distribution that satisfies the selected input-output OAM mode group mapping relationship can be solved.

[0088] Step S40: Arrange the metasurface antennas according to the phase distribution and the electromagnetic response curve to form a multi-level cascaded metasurface device.

[0089] It should be noted that the antenna structure of the metasurface can be arranged according to the solved phase distribution and the response of the metasurface unit structure to form a cascaded metasurface device.

[0090] In a possible implementation, the metasurface unit material is a sandwich structure of copper-Rogers5880 plate-copper, and the unit period is 600 μm. The number of unit structures of each layer of the metasurface device is 100×100. The number of cascaded layers is 3. It should be noted that the number of layers and the number of unit structures of the metasurface are not limited to the above values and can be fine-tuned according to the regulation function. Since this metamolecule has the property of polarization conversion, when arranging the metasurface, it is necessary to rotate the grid direction on the even layers to match the polarization mode. For example, the arrangement of the 3-level cascaded metasurface for horizontal polarization and vertical polarization incidence is as Figure 7and Figure 8 As shown Figure 7 Fig. is a schematic structural diagram of horizontal polarization incidence in the first embodiment of the method for constructing a routing device according to the present invention Figure 8 Fig. is a schematic structural diagram of vertical polarization incidence in the first embodiment of the method for constructing a routing device according to the present invention. Among them, OAM 1-n is the incident beam carrying orbital angular momentum, and Gauss 1 , Gauss n are the metasurface unit structures of the emitted Gaussian beams. In order to reduce experimental errors, the interlayer distance of the cascaded metasurface is consistent with the diffraction distance set in the model. After the phase modulation of different OAM modes by the cascaded metasurface device, they will diffract to different angles, thereby realizing two-dimensional space routing

[0091] In this embodiment, the metasurface unit structure is designed according to the electromagnetic response curve covering [0-2π]; a multi-level phase model is constructed, and the target input and output orbital angular momentum mode field distributions are designed; the phase distribution of the multi-level phase modulation model is obtained according to the target input and output orbital angular momentum mode field distributions; the metasurface antennas are arranged according to the phase distribution and the electromagnetic response curve to form a multi-layer cascaded metasurface device. By cascading multiple metasurface devices and using their progressive beam phase control mechanism, a complex mapping relationship of the orbital angular momentum mode group is established, and then the terahertz routing communication application of multiplexing orbital angular momentum modes is realized

[0092] Referring to Figure 9 , Figure 9 Fig. is a schematic flow chart of the second embodiment of the method for constructing a routing device according to the present invention. As shown Figure 9 in this embodiment, the same or similar content as that in the above embodiment can be referred to the above introduction and will not be repeated hereinafter. After the step S30, the following steps are further included

[0093] Step S301: Use the complex mean square error distribution as the error function between the target input and output orbital angular momentum mode field distributions and the actual field distribution

[0094] Step S302: Use adaptive moment estimation optimization to obtain the target input and output orbital angular momentum mode field distributions in which the loss function converges to the target loss value

[0095] It should be noted that for the solution of the phase diffraction matrix parameters of the cascaded metasurface, the gradient descent algorithm can be used as an example to solve the mapping relationship that satisfies a specific OAM mode group. The calculation process of this algorithm is as follows

[0096] First, an error function is set to measure the difference between the field distribution after cascaded phase modulation processing and the ideal field distribution. Here, the complex mean square error distribution is selected as the error function, and its corresponding mathematical description is as follows

[0097] L(x,y) = [|Y ′ (x,y) - Y(x,y)| 2

[0098] where Y ′ (x,y) represents the forward transmission result of the electromagnetic field, and Y(x,y) represents the ideal electromagnetic field distribution.

[0099] Subsequently, set the target input-output OAM mode vector group, forward-transmit the electric field to the plane where the output vector group is located, and obtain the corresponding complex amplitude distribution field. Calculate the gradient value of the output electric field plane with respect to the components in each phase plane:

[0100] m t = β 1 m t-1 + (1 + β 1 )g t

[0101] where m t is the first moment at time t. Among them, β 1 is the decay coefficient of the first moment estimation, with a default value of 0.9, and the default value of the first moment estimation m 0 = 0. g t is the gradient value. Further calculate the second moment estimation:

[0102]

[0103] where v t is the second moment value at time t, and the initial value of the second moment v 0 = 0. By performing bias correction on the first and second moments, the corresponding corrected moment components and are obtained and used as new parameters to update the phase value:

[0104]

[0105] where α is the learning rate, with a default value of 0.001, which is used to adjust the parameter update speed, and ε is a constant to avoid division by zero, with a default value of 0.1. The above optimization process is also called Adaptive Moment Estimation (Adam) optimization, which is one of the most commonly used optimization methods in the field of deep learning. After 3000 iterations, the loss function converges to a local minimum. Then, the phase matrix distribution that satisfies the corresponding OAM mode group conversion function can be obtained.

[0106] In a possible implementation, an example of using a cascaded metasurface to achieve angular routing of terahertz OAM modes is described. As Figure 10 ​As shown Figure 10 is a schematic structural diagram of the second embodiment of the method for constructing a routing device of the present invention. In Figure 10 , the sampling space size is 500×500, and the unit size is 600um. The number of input OAM mode groups is 8, and the mode selection range is non-zero modes from -4 to +4. The direction of the output Gaussian beam is 8. It should be noted that the selected OAM modes and numbers are not limited to the above values. According to the given input and output mode groups, combined with the gradient descent algorithm, the 3-layer phase matrix distribution as shown in Figure 7 is calculated. The results show that the three-layer phase matrix distribution can independently respond to 8 OAM modes, and angularly route different OAM modes to different two-dimensional planes respectively.

[0107] In this embodiment, the complex mean square error distribution is used as the error function between the target input and output orbital angular momentum mode field distributions and the actual field distributions; the adaptive moment estimation optimization is used to obtain the target input and output orbital angular momentum mode field distributions in which the loss function converges to the target loss value. The alternating product of the phase diffraction matrix and the transmission matrix can be realized to establish the mapping of the OAM mode group, and then simultaneously respond to multiple OAM modes to achieve efficient angular selectivity routing control. The phase matrix is further solved by the gradient descent algorithm, and the optimal phase matrix distribution is obtained by minimizing the error function. The terahertz OAM mode beam is gradually regulated by the metasurface, and then the angular selectivity routing of the OAM mode group is realized, providing an efficient mode demodulation technology for the terahertz channel to achieve a communication rate of the Tbps level.

[0108] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural or equivalent process transformation made by using the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

[0109] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0110] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative position relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0111] In addition, the descriptions involving "first", "second", etc. in the present invention are for descriptive purposes only, and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments may be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. A terahertz orbital angular momentum mode router device, characterized in that: The terahertz orbital angular momentum mode router device comprises: a multi-layer cascaded metasurface device; Each of the metasurface devices comprises: a metasurface unit structure distributed in a two-dimensional plane; The metasurface unit structure comprises: a grid structure, a dielectric plate and an antenna structure arranged in sequence; The grid structure and the antenna structure are respectively arranged on two sides of the dielectric layer; By adjusting the geometric parameters of the metasurface unit structure, a frequency domain finite element simulation is performed to obtain an electromagnetic response curve covering [0-2π]; Constructing the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distribution; The antenna structure is arranged according to the phase distribution and the electromagnetic response curve to form a multi-layer cascaded metasurface device.

2. The terahertz orbital angular momentum mode routing device according to claim 1, characterized in that: The grid structure is made of copper or gold metal material; The grid structure is rectangular metal with the same spacing, and the spacing matches the wavelength of the electromagnetic wave; The grid structure is used to filter electromagnetic waves with preset polarization and enhance electromagnetic response.

3. The terahertz orbital angular momentum mode routing device according to claim 2, characterized in that: The antenna structure is made of copper or gold metal material; The shape and geometric parameters of the antenna structure are set according to the electromagnetic response curve; The antenna structure is used for polarization conversion and superimposing a specific phase delay.

4. The terahertz orbital angular momentum mode routing device according to claim 3, characterized in that: The material of the dielectric plate is selected from resin glass with low dielectric constant and loss factor; By adjusting the dielectric thickness of the dielectric plate, the thickness of the grid structure and the thickness of the antenna structure, a preset terahertz frequency band is obtained.

5. A method for constructing a router component, characterized in that: The router device construction method is used to construct the terahertz orbital angular momentum mode router device as claimed in any one of claims 1 to 4, and the steps of the router device construction method include: Design the metasurface unit structure based on the electromagnetic response curve covering [0-2π]; Construct a multi-level phase model and design the target input and output orbital angular momentum mode field distribution; Acquire the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distribution; The metasurface antennas are arranged according to the phase distribution and the electromagnetic response curve to form a multi-layer cascaded metasurface device.

6. The method for constructing a router device according to claim 5, characterized in that: The steps of constructing a multi-level phase model and designing target input and output orbital angular momentum mode field distributions include: Construct the Laguerre-Gaussian model as a mathematical expression model of the input electromagnetic field distribution; The beam radial index in the Laguerre-Gaussian mode is set to 0, and different angular indices are used to obtain the corresponding angular momentum mode field distribution.

7. The method for constructing a router device according to claim 6, characterized in that: The step of setting the beam radial index in the Laguerre-Gaussian mode to 0 and using different angular indices to obtain the corresponding angular momentum mode field distribution comprises: Setting the beam radial index in the Laguerre-Gaussian mode to 0, and using different angular indices to obtain corresponding angular momentum modes; The target input field distribution is formed by using the electromagnetic field distribution located at the center; The target output field distribution is formed by superimposing the gradient phase distribution on the electromagnetic field distribution located at the center to guide the transmission direction of the output electromagnetic field.

8. The method for constructing a router device according to claim 7, characterized in that: The step of acquiring the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distribution comprises: Construct a mathematical model of progressive modulation of multiple phase planes; The objective function of the mathematical model of the progressive modulation is set, and the phase distribution that satisfies the target input and output orbital angular momentum mode field distribution is solved according to the gradient descent algorithm.

9. The method for constructing a router device according to claim 8, characterized in that: After the step of acquiring the phase distribution of the multi-level phase modulation model according to the target input and output orbital angular momentum mode field distribution, the method further includes: The complex mean square error distribution is used as the error function between the target input and output orbital angular momentum mode field distribution and the actual field distribution; Adaptive moment estimation optimization is used to obtain target input and output orbital angular momentum mode field distributions where the loss function converges to within the target loss value.

10. The method for constructing a router device according to claim 9, characterized in that: The step of arranging the metasurface antennas according to the phase distribution and the electromagnetic response curve to form a multi-layer cascaded metasurface device comprises: Arranging metasurface antennas according to the phase distribution and the electromagnetic response curve; The direction of the grid structure is rotated in the even-numbered layers according to the polarization mode, a metasurface unit structure is constructed on the dielectric plate, and a multi-layer cascaded metasurface device is formed according to the phase distribution.

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