Anti-eavesdropping terahertz vortex beam communication system and method based on dynamic topological charge

Abstract

The present invention relates to an anti-eavesdropping terahertz vortex beam communication system and method based on dynamic topological charge, belonging to the field of confidential communication technology, wherein the terahertz transmitter A is used to transmit useful signals, and sequentially passes through a horn antenna A, a terahertz lens A, a terahertz vortex beam generator A, and enters a beam combining cube through a reflector, and the terahertz transmitter B is used to transmit interference signals, and sequentially passes through a horn antenna B, a terahertz lens B, and a terahertz vortex beam generator B to enter the beam combining cube, and after the useful signal and the interference signal are transmitted in free space, they sequentially pass through a terahertz vortex beam generator C, an aperture, a terahertz lens C, and a horn antenna C to enter a terahertz receiver. The present invention comprehensively analyzes the existing terahertz communication technology and vortex beam generation method, and proposes an anti-eavesdropping terahertz vortex beam communication system and method based on dynamic topological charge, aiming to further improve the confidentiality of the terahertz communication system.

Description

Technical Field

[0001] The present invention provides an anti-eavesdropping terahertz vortex beam communication system and method based on dynamic topological charge, belonging to the technical field of confidential communication. Background Art

[0002] Terahertz waves refer to electromagnetic waves with a frequency range of 0.1THz~10THz, which is between infrared light and millimeter waves. Due to its band characteristics, terahertz communication integrates the characteristics of microwave communication and optical communication, and has many advantages such as fast transmission rate, large capacity, strong directionality, high security and good penetration, and has high research value. The propagation of terahertz waves in the atmosphere is greatly affected by water molecules, so it is mainly used for short-distance communication in the atmosphere. It is precisely because of the short transmission distance that the confidentiality performance is increased, and it has important application value in the military field. In outer space, without the influence of the atmosphere, terahertz waves can be transmitted almost losslessly, and long-distance communication can be achieved with very small power. Therefore, terahertz waves also have important application prospects in satellite communications. It can be seen that terahertz communication technology has an important position in the 21st century with highly developed informatization.

[0003] At present, terahertz communication technology is mainly divided into two types, one is all-electronic technology and the other is photonic technology. All-electronic technology has the characteristics of miniaturization and easy integration, and it mainly relies on semiconductor integrated circuits. Domestic and foreign units such as Nippon Telegraph and Telephone Corporation (NTT), University of Electronic Science and Technology of China, and Huazhong University of Science and Technology have conducted relatively in-depth research on all-electronic terahertz communication technology, and have conducted detailed tests on important parameters such as the propagation characteristics, spectrum efficiency, and communication rate of terahertz waves in different bands. Compared with all-electronic technology, photonic technology has higher transmission capacity. The core of this technology is the single-carrier photodiode (UTC-PD) designed and produced by NTT. This diode can provide higher output power and larger bandwidth, so it is very suitable for long-distance and high-speed terahertz communication. Due to the limitations of semiconductor devices, the mainstream frequency band of all-electronic technology is basically below 300GHz, while the frequency band of photonic technology can reach above 300GHz due to the existence of UTC-PD.

[0004] The transmission method of traditional wireless communication makes the information at risk of eavesdropping during transmission. Once the transmitted message is eavesdropped, it will have a great impact on both parties. In daily life, if the content of wireless communication is eavesdropped, personal information may be sold at the least, or even suffer from network fraud; in the military field, once the transmitted message is stolen and deciphered, it will cause incalculable losses to the national defense cause. Therefore, in wireless communication technology, the study of anti-eavesdropping means has always been an important research direction. Traditional anti-eavesdropping is mainly achieved through means such as keys and artificial noise. With the development of artificial intelligence and the enhancement of computer data processing capabilities, exhaustive methods, reverse methods and other cracking methods have emerged in an endless stream, and traditional anti-eavesdropping means have been greatly challenged. As an emerging technology, vortex beam communication has unique advantages in anti-eavesdropping.

[0005] A vortex beam is a type of beam with an annular intensity distribution and a spiral wavefront structure. It has orbital angular momentum, and the orbital angular momentum state carried by its Laguerre-Gaussian mode is also called topological charge. Since the orbital angular momentum states of different topological charges are orthogonal to each other and the eigenstate is multidimensional, the orbital angular momentum of the beam can be used to transmit and carry information, and multiple information can be transmitted on the same path without additional spectrum broadening. At the same time, vortex signal demodulation can only be successfully achieved if the topological charge numbers of the vortex phase modulation devices at the receiving end and the transmitting end are opposite. Therefore, the vortex beam communication method greatly improves the communication channel capacity, spectrum efficiency and confidentiality. As a result, people gradually extend the carrier of information in communication from the amplitude, polarization, frequency and phase of the beam to the orbital angular momentum, and use the orbital angular momentum of the vortex beam as a new carrier degree of freedom, which greatly increases the channel capacity of the communication system, and this type of communication system is called a vortex beam communication system.

[0006] The generation of vortex beams has always been the focus of vortex beam communication systems. At present, the methods of vortex beam generation are mainly divided into intracavity generation and extracavity generation. The intracavity generation method refers to the processing of the laser in the resonant cavity when it is generated, so that a vortex beam with a specific topological charge is generated. This method is mainly used for the generation of low-order vortex beams and is not applicable to the terahertz band. The extracavity generation method refers to the use of other devices in space, such as spiral phase plates, spatial modulators, q-plates, metasurfaces, etc., to give the incident beam a spiral phase to turn it into a vortex beam. This method has high conversion efficiency and can obtain vortex beams with a specific topological charge as needed. It is small in size, but is subject to the processing accuracy of the device. However, no matter which method is used, the topological charge of the vortex beam generated is fixed, and there is still a risk of being brute-forced by exhaustive eavesdropping. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention comprehensively analyzes the existing terahertz communication technology and vortex beam generation method, and proposes an anti-eavesdropping terahertz vortex beam communication system and method based on dynamic topological charge, aiming to further improve the confidentiality of the terahertz communication system.

[0008] The technical solution of the present invention is:

[0009] A terahertz vortex beam communication system for preventing eavesdropping based on dynamic topological charge, comprising a terahertz transmitter A, a terahertz transmitter B, a horn antenna A, a horn antenna B, a horn antenna C, a terahertz lens A, a terahertz lens B, a terahertz lens C, a terahertz vortex beam generator A, a terahertz vortex beam generator B, a terahertz vortex beam generator C, a beam combining cube, a reflector and an aperture;

[0010] The terahertz transmitter A is used to transmit useful signals, and passes through horn antenna A, terahertz lens A, terahertz vortex beam generator A, and a reflector to enter the beam combining cube. The terahertz transmitter B is used to transmit interference signals, and passes through horn antenna B, terahertz lens B, and terahertz vortex beam generator B to enter the beam combining cube. After the useful signal and the interference signal are transmitted in free space, they pass through terahertz vortex beam generator C, an aperture, terahertz lens C, and horn antenna C to enter the terahertz receiver.

[0011] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge is implemented based on the above-mentioned anti-eavesdropping terahertz vortex beam communication system based on dynamic topological charge, comprising the following steps:

[0012] (1) The useful signal is transmitted from the terahertz transmitter A through the horn antenna A, collimated by the terahertz lens A, and then input into the terahertz vortex beam generator A. After being reflected by the reflector, the signal enters the beam combining cube.

[0013] (2) The terahertz transmitter B transmits the interference signal, which is then transmitted through the horn antenna B, collimated by the terahertz lens B, and then input into the terahertz vortex beam generator B. The interference signal is then combined with the useful signal in the beam combining cube for coaxial transmission.

[0014] (3) After the useful signal and the interference signal are transmitted in free space for a certain distance, they are incident on the terahertz vortex beam generator C for dehelix;

[0015] (4) The dehelixed beam is then filtered by the aperture, retaining only the part with a topological charge of 0. It is then converged to the horn antenna C through the terahertz lens C and detected and processed by the terahertz receiver.

[0016] Preferably, in step (1) and step (2), terahertz transmitter A and terahertz transmitter B use photonic transmitters or electronic transmitters.

[0017] Preferably, in step (1), the terahertz vortex beam generator A modulates the useful signal using a pre-agreed variation rule.

[0018] Preferably, in step (2), the terahertz vortex beam generator B adopts a different variation rule from that of the terahertz vortex beam generator A. It is worth noting that the topological charge of the terahertz vortex beam generator A and the topological charge of the terahertz vortex beam generator B must not be equal in any same time period, otherwise crosstalk will occur between the useful signal and the interference signal.

[0019] Preferably, in step (3), the terahertz vortex beam generator C adopts a topological charge change law that is conjugate with the terahertz vortex beam generator A, and can de-spiralize the vortex signal component carrying the useful signal into a beam with a topological charge equal to 0, while the vortex signal component carrying the interference signal is still a vortex beam with a spiral phase characteristic, thereby achieving separation of the useful signal and the interference signal.

[0020] Preferably, in step (4), according to the characteristics of the vortex beam, the intensity distribution of the useful signal with a topological charge of 0 is a solid circle, while the intensity distribution of the interference signal with a topological charge of not 0 is a circular ring. The two are concentric and the inner diameter of the circular ring is larger than the diameter of the solid circle. The ring is filtered out using an aperture, and only the circle in the center is retained, so that the two signals can be separated.

[0021] Preferably, the terahertz vortex beam generator A, the terahertz vortex beam generator B and the terahertz vortex beam generator C have the same structure, and are all composed of two terahertz metasurfaces and a packaging shell, wherein the terahertz metasurface adopts a transmission phase type metasurface, the terahertz metasurface includes a substrate and a metasurface radiation unit, and the metasurface radiation unit adopts a cylindrical structure, and the transmission optical path of the incident terahertz wave is changed by adjusting the diameter of the cylinder, thereby realizing phase regulation;

[0022] Two conjugated transmission phase-type metasurfaces are placed opposite to each other to form a double-layer moiré structure, so that the joint transmission function and joint phase are equal to the superposition of the transmission functions and phases of the two metasurfaces; in order to facilitate the quantitative control of the modulated topological charge, one transmission phase-type metasurface is fixed and the other transmission phase-type metasurface is manipulated using a rotating table to achieve rotation at a specific angle, thereby realizing continuous adjustment of the topological charge.

[0023] Preferably, the terahertz metasurface is manufactured based on the electrojet printing technology, which is implemented by an electrojet printing device, which includes a high-voltage power supply, a nozzle, and a collecting plate, wherein a substrate for preparing the metasurface is placed on the collecting plate, and a liquid of the prepared metasurface material is contained in the nozzle, and its internal air pressure is controlled by an air pressure control system; the collecting plate and the nozzle are respectively connected to two electrodes of the high-voltage power supply, and when voltage is applied to the two, the liquid in the nozzle will be affected by the electric field force to form a curved liquid surface in a cone shape, which is called a Taylor cone. When the applied electric field force is large enough, the droplets will spray out jets or droplets from the tip of the Taylor cone;

[0024] Preferably, photosensitive resin 9400 is used as the super surface material, and silicon dioxide is used as the base material.

[0025] Preferably, one terahertz metasurface is mounted on a fixed base, and the other terahertz metasurface is mounted on a rotating platform. Initially, the two terahertz metasurfaces are placed facing each other by controlling the rotating platform, that is, the joint transmission phase is zero, and then the relationship between the rotation angle and the topological charge change is calibrated at different frequencies, thereby achieving continuous adjustable topological charge under broadband.

[0026] Preferably, the rotating stage is controlled by a programmable electric motor. Before communication, the transmitting end and the receiving end agree on the change rule of the topological charge, and use a computer to program the electric motor to achieve quantitative control, thereby achieving continuous change of the topological charge; during the communication process, the topological charge number always keeps changing dynamically;

[0027] By programming and controlling the dynamic change interval of the topological charge, the difficulty of eavesdropping is further increased.

[0028] For any details not provided in the present invention, please refer to the prior art.

[0029] The beneficial effects of the present invention are:

[0030] 1. The anti-eavesdropping terahertz vortex beam communication system based on the dynamic topological charge of the terahertz metasurface vortex beam generator used in the present invention can only realize vortex demodulation of the vortex communication signal when the modulated topological charge numbers of the terahertz metasurface vortex beam generator at the transmitting end and the receiving end are opposite, thereby improving the confidentiality of the terahertz communication system.

[0031] 2. The anti-eavesdropping terahertz vortex beam communication system based on the dynamic topological charge of the terahertz metasurface vortex beam generator used in the present invention can keep the topological charges of the useful signal and the interference signal synchronously changing dynamically, preventing the eavesdropper from brute force cracking and eavesdropping in an exhaustive manner, which can further greatly improve the confidentiality of the terahertz communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0033] Figure 1 Schematic diagram of vortex beam intensity distribution;

[0034] Figure 2 Schematic diagram of vortex beam phase distribution;

[0035] Figure 3 Schematic diagrams of terahertz metasurfaces, where (a) is a schematic diagram of a single-chip terahertz metasurface; (b) is a schematic diagram of a double-layer moiré structure;

[0036] Figure 4 This is the structural diagram of the electrojet printing equipment;

[0037] Figure 5 This is the force analysis diagram of Taylor cone;

[0038] Figure 6 This is a schematic diagram of the packaging shell of the terahertz metasurface vortex beam generator;

[0039] Figure 7 The block diagram of the anti-eavesdropping vortex communication system model with dynamic topology load;

[0040] Figure 8 A schematic diagram of a terahertz vortex beam communication system that is resistant to eavesdropping;

[0041] Fig. 9 It is a schematic diagram of the strength of the useful signal and the interference signal after they are combined;

[0042] Fig.10 It is a schematic diagram of the intensity of the useful signal and the interference signal after dehelical processing;

[0043] Fig.11 Schematic diagram of the intensity of the useful signal and interference signal before and after passing through the aperture after de-helicalization.

[0044] Among them, 1- horn antenna A, 2- terahertz lens A, 3- terahertz vortex beam generator A, 4- reflector, 5- horn antenna B, 6- terahertz lens B, 7- terahertz vortex beam generator B, 8- beam combining cube, 9- terahertz vortex beam generator C, 10- aperture, 11- terahertz lens C, 12- horn antenna C, 13- high voltage power supply, 14- nozzle, 15- collecting plate, 16- substrate, 17- Taylor cone, 18- atmospheric pressure, 19- surface tension, 20- normal electric field force, 21- tangential electric field force, 22- gravity, 23- inner wall of nozzle, 24- fixed base, 25- rotating table, 26- rotating table motor, 27- air pump, 28- terahertz transmitter A, 29- terahertz transmitter B, 30- terahertz receiver, 31- eavesdropper. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the implementation of this specification, but are not limited to this. Anything not fully described in the present invention shall be based on the conventional technology in the art.

[0046] Example 1

[0047] An anti-eavesdropping terahertz vortex beam communication system based on dynamic topological charge, such as Figure 8 As shown, it includes a terahertz transmitter A 28, a terahertz transmitter B 29, a horn antenna A 1, a horn antenna B 5, a horn antenna C 12, a terahertz lens A2, a terahertz lens B 6, a terahertz lens C 11, a terahertz vortex beam generator A 3, a terahertz vortex beam generator B7, a terahertz vortex beam generator C 9, a beam combining cube 8, a reflector 4 and an aperture 10;

[0048] The terahertz transmitter A is used to transmit useful signals, and the signals pass through the horn antenna A1, the terahertz lens A2, the terahertz vortex beam generator A3, and the reflector 4 to enter the beam-combining cube 8. The terahertz transmitter B is used to transmit interference signals, and the signals pass through the horn antenna B5, the terahertz lens B6, and the terahertz vortex beam generator B7 to enter the beam-combining cube 8. After the useful signals and the interference signals are transmitted in free space, the signals pass through the terahertz vortex beam generator C9, the aperture 10, the terahertz lens C11, and the horn antenna C12 to enter the terahertz receiver 30.

[0049] The block diagram of the anti-eavesdropping vortex communication system model based on dynamic topological charge is as follows: Figure 7 shown.

[0050] Example 2

[0051] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge comprises the following steps:

[0052] (1) The useful signal is transmitted by the terahertz transmitter A through the horn antenna A1, collimated by the terahertz lens A2, and then input into the terahertz vortex beam generator A3, reflected by the reflector 4, and then incident on the beam combining cube 8;

[0053] (2) The terahertz transmitter B transmits the interference signal, which is sent through the horn antenna B5 and collimated by the terahertz lens B6 before being input into the terahertz vortex beam generator B7. The signal is then combined with the useful signal in the beam combining cube 8 for coaxial transmission. The intensity diagram of the combined useful signal and interference signal is shown in Figure 1. Fig. 9 As shown;

[0054] (3) After the useful signal and the interference signal are transmitted in free space for a certain distance, they are incident on the terahertz vortex beam generator C 9 for dehelix, as shown in Fig.10 As shown;

[0055] (4) The dehelixed beam is then filtered by aperture 10, retaining only the part with a topological charge of 0, as Fig.11 As shown, the light is converged to the horn antenna C12 through the terahertz lens C11 and detected and processed by the terahertz receiver.

[0056] Example 3

[0057] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge is as described in Example 2, except that in step (1) and step (2), terahertz transmitter A and terahertz transmitter B use photonic transmitters or electronic transmitters.

[0058] Example 4

[0059] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge, as described in Example 3, except that in step (1), the terahertz vortex beam generator A modulates the useful signal using a pre-agreed change rule, such as a preset random integer sequence topological charge: l 1 =1, 3, -5, 2, 4, -9, 10..., changes every 2 seconds. Figure 1 , Figure 2 They are schematic diagrams of the intensity distribution and phase distribution of a vortex beam respectively.

[0060] In step (2), the interference signal is used to further prevent the eavesdropper 31 from obtaining the useful signal and enhance the confidentiality of the system. The terahertz vortex beam generator B adopts a different change rule from the terahertz vortex beam generator A, such as the topological charge value is: l 2= l 1 + n ( n is a randomly generated integer), which changes every 2 seconds. It is worth noting that l 1 and l 2 shall not be equal in any identical period of time (i.e. n ≠0), otherwise crosstalk will occur between the useful signal and the interference signal.

[0061] In step (3), the terahertz vortex beam generator C adopts a topological charge change law that is conjugate with the terahertz vortex beam generator A, that is, l 1 The corresponding topological charge of the opposite number sequence is: l 3 =-1, -3, 5, -2, -4, 9, -10..., the vortex signal component carrying the useful signal can be de-spiralized into a beam with a topological charge equal to 0, while the vortex signal component carrying the interference signal is still a vortex beam with a spiral phase characteristic, thereby realizing the separation of the useful signal and the interference signal. l 1 In this case, the useful signal cannot be effectively separated from the interference signal. At the same time, based on the synchronization of the useful signal and the interference signal to keep the topological charge dynamically changing, the eavesdropper 31 cannot obtain the topological charge value and its characteristics of the useful signal by exhaustive method.

[0062] In step (2), the difficulty of eavesdropping by the eavesdropper 31 can be further increased by increasing the number of interference signal channels, thereby enhancing the confidentiality of the system. Based on the orthogonal nature of the orbital angular momentum states of different topological charges of the vortex beam, the transmission of useful signals will not be affected by crosstalk.

[0063] The number of interference signal channels is the number of interference signals, where the topological charge of each interference signal is different from each other and also different from the topological charge of the useful signal. In theory, it is only limited by hardware conditions and costs. For example, the vortex beam generator can achieve different modulation ranges according to the design parameters. Assuming that it can achieve continuous modulation of the topological charge from -N to +N, the total number of available signal channels is 2N+1. If the number of useful signal channels is M, the interference signal is allowed to increase to 2N+1-M at most. However, each additional channel signal requires an increase in the cost of a set of transmitting-end terahertz transmitters and vortex beam generators and other devices.

[0064] Example 5

[0065] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge, as described in Example 4, except that in step (4), according to the characteristics of the vortex beam, the useful signal intensity distribution with a topological charge of 0 is a solid circle (such as Fig.11 The middle circle in the leftmost figure), while the interference signal strength distribution of the topological charge is not 0 is a circular ring (such as Fig.11 The outer ring in the leftmost figure) is concentric with the inner diameter of the ring larger than the diameter of the solid circle. Use an aperture (such as Fig.11 The ring is filtered out (the middle figure) and only the circle in the center is retained, thus achieving separation of the two signals.

[0066] Example 6

[0067] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge, as described in Example 5, except that the terahertz vortex beam generator A, the terahertz vortex beam generator B and the terahertz vortex beam generator C have the same structure, and are all composed of two terahertz metasurfaces and a packaging shell, and the packaging shell is as follows Figure 6 As shown in FIG, the terahertz metasurface adopts a transmission phase metasurface and is designed based on a double-layer moiré structure. Figure 3 As shown in (a), the transmission phase type metasurface changes the equivalent refractive index by changing the unit structure or thickness of the metasurface, thereby realizing the regulation of the transmission phase. The terahertz metasurface includes a substrate and a metasurface radiation unit. The metasurface radiation unit adopts a cylindrical structure. The transmission optical path of the incident terahertz wave is changed by adjusting the diameter of the cylinder, thereby realizing the regulation of the phase.

[0068] Two conjugated transmission phase metasurfaces are placed opposite to each other to form a double-layer moiré structure, such as Figure 3 As shown in (b), the joint transmission function and joint phase are equal to the superposition of the transmission functions and phases of the two metasurfaces; in order to facilitate the quantitative control of the modulated topological charge, one transmission phase-type metasurface is fixed and the other transmission phase-type metasurface is manipulated using a rotating table to achieve a specific angle of rotation, thereby achieving continuous adjustable topological charge.

[0069] The joint transmission function and joint phase of two conjugate metasurfaces are equal to the superposition of the metasurface transmission function and phase:

[0070] (1)

[0071] in, is the joint transfer function, For the joint phase, i is an imaginary unit, and Respectively represent the phase distribution of the first metasurface and the second metasurface, there are:

[0072] (2)

[0073] in, a It is a design parameter used to control the adjustment relationship between the rotation angle of two metasurfaces and the topological charge. If a is too large, it will affect the processing difficulty. It is generally a positive integer not exceeding 10, for example, a=2. N is a positive integer, m Determined by the following formula:

[0074] (3)

[0075] in, is from 0 to 2 in polar coordinates π Angle, ; round ( ) represents the rounding function;

[0076] Therefore, the phase distribution of the entire metasurface is obtained as follows:

[0077] (4)

[0078] in θ is the angle of rotation of the second metasurface compared to the first one, which can be simplified to:

[0079] (5)

[0080] And because the phase and angle of the vortex beam have the following relationship:

[0081] (6)

[0082] Therefore, the topological charge has the following linear relationship with the rotation angle of the metasurface:

[0083] (7)

[0084] In summary, rotating the second transmission phase-type metasurface can obtain high-quality modulation of different topological charges. When rotating clockwise, a positive topological charge can be generated, and vice versa, a negative topological charge can be generated.

[0085] Example 7

[0086] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge, as described in Example 6, except that the terahertz metasurface is manufactured based on electrospray printing technology, which is one of the important technologies for metasurface processing. Its working principle is to eject liquid from a nozzle by applying an external electric field to form droplets or jets with a diameter much smaller than the nozzle diameter, and then move the nozzle through precise displacement control to directly write the desired metasurface structure. Figure 4 As shown, the electrospray printing technology is realized by an electrospray printing device, which includes a high-voltage power supply 13, a nozzle 14, and a collecting plate 15, wherein a substrate 16 on which a metasurface is to be prepared is placed on the collecting plate 15, and a liquid of the prepared metasurface material is contained in the nozzle 14, and the nozzle 14 is connected to an air pump 27, and its internal air pressure is controlled by an air pressure control system; the collecting plate 15 and the nozzle 14 are respectively connected to two electrodes of the high-voltage power supply 13, when voltage is applied to the two, the liquid in the nozzle 14 will be affected by the electric field force to form a curved liquid surface in a cone shape, which is called a Taylor cone 17, and when the applied electric field force is large enough, the droplets will spray out jets or droplets from the tip of the Taylor cone 17; as shown in FIG. Figure 5 In the figure, 18 represents atmospheric pressure, 19 represents surface tension, 20 represents normal electric force, 21 represents tangential electric force, 22 represents gravity, and 23 represents the inner wall of the nozzle. The viscosity and conductivity of the liquid, the amplitude and frequency of the voltage, and the air pressure will all affect the flow rate and size of the jet or droplet.

[0087] Preferably, photosensitive resin 9400 is used as the super surface material and silicon dioxide is used as the base material. Silicon dioxide is placed in the center of the collecting plate, and the process parameters suitable for the photosensitive resin are found by continuously adjusting the voltage amplitude, frequency, and air pressure. After the production is completed, the photosensitive resin can be cured by ultraviolet irradiation.

[0088] Example 8

[0089] A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge, as described in Example 7, the difference is that for the above-mentioned terahertz metasurface, a rotating table and a fixed base are used for packaging and integration. One terahertz metasurface is installed on a fixed base 24, and the other terahertz metasurface is installed on a rotating table 25, and the rotating table can be controlled by a powered rotating table motor 26. There are circular holes in the center of the fixed base and the rotating table, and there are threads in the holes. When installing, first place the terahertz metasurface in the hole, and then screw a clamp from each side to fix the metasurface. For example, the diameter of the metasurface is 2 inches (50.8mm), and the diameter of the hole is also 50.8mm. Put the metasurface into the hole, and then screw a clamp from both sides of the hole to clamp the metasurface to fix it. The clamp can refer to Sorebo's SM2RR, and a special sleeve is used to screw the clamp, and the sleeve can refer to Sorebo's SM2M30. Initially, the two terahertz metasurfaces are placed facing each other by controlling the rotating stage, that is, the joint transmission phase is zero. Then, the relationship between the rotation angle and the change of topological charge is calibrated at different frequencies, thereby achieving continuous adjustment of topological charge under broadband conditions.

[0090] Preferably, the rotating table is controlled by a programmable electric motor. Before communication, the transmitting end and the receiving end agree on the change rule of the topological charge, and use a computer to program the electric motor to achieve quantitative control, thereby achieving continuous change of the topological charge; during the communication process, the topological charge number always keeps changing dynamically; when the eavesdropper 31 is unknown to the transmission signal situation and the change rule of the topological charge of the transmitting end, even if the eavesdropper 31 receives the emitted terahertz signal, it cannot perform vortex demodulation and subsequent data decoding on it, and cannot obtain communication information, which greatly improves the confidentiality of the system.

[0091] The topological charge change interval can be further reduced according to the rotation performance index of the rotating table used, and the dynamic change interval of the topological charge number can even be controlled by programming, thereby further increasing the difficulty of eavesdropping by the eavesdropper 31 and enhancing the confidentiality of the system.

[0092] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An anti-eavesdropping terahertz vortex beam communication system based on dynamic topological charge, characterized in that: Including terahertz transmitter A, terahertz transmitter B, horn antenna A, horn antenna B, horn antenna C, terahertz lens A, terahertz lens B, terahertz lens C, terahertz vortex beam generator A, terahertz vortex beam generator B, terahertz vortex beam generator C, beam combining cube, reflector and aperture; The terahertz transmitter A is used to transmit useful signals, and sequentially passes through the horn antenna A, the terahertz lens A, the terahertz vortex beam generator A, and the reflector to enter the beam combining cube. The terahertz transmitter B is used to transmit interference signals, and sequentially passes through the horn antenna B, the terahertz lens B, and the terahertz vortex beam generator B to enter the beam combining cube. After the useful signal and the interference signal are transmitted in free space, they sequentially pass through the terahertz vortex beam generator C, the aperture, the terahertz lens C, and the horn antenna C to enter the terahertz receiver. Terahertz vortex beam generator A, terahertz vortex beam generator B and terahertz vortex beam generator C have the same structure, and are all composed of two terahertz metasurfaces and a packaging shell, wherein the terahertz metasurface adopts a transmission phase type metasurface, and the terahertz metasurface includes a substrate and a metasurface radiation unit, and the metasurface radiation unit adopts a cylindrical structure, and the transmission optical path of the incident terahertz wave is changed by adjusting the diameter of the cylinder, thereby realizing phase regulation; Two conjugated transmission phase metasurfaces are placed opposite to each other to form a double-layer moiré structure, so that the joint transmission function and joint phase are equal to the superposition of the transmission functions and phases of the two metasurfaces. To facilitate quantitative control of the modulated topological charge, one transmission phase metasurface is fixed and the other is manipulated by a rotating table to achieve a specific angle of rotation, thereby achieving continuous adjustment of the topological charge. One terahertz metasurface is mounted on a fixed base, and the other terahertz metasurface is mounted on a rotating platform. Initially, the two terahertz metasurfaces are placed facing each other by controlling the rotating platform, that is, the joint transmission phase is zero. Then, the relationship between the rotation angle and the change of topological charge is calibrated at different frequencies, thereby achieving continuous adjustment of topological charge under broadband. The rotating table is controlled by a programmable electric motor. Before communication, the transmitter and the receiver agree on the change rules of the topological charge, and use a computer to program the electric motor to achieve quantitative control, thereby achieving continuous change of the topological charge. During the communication process, the topological charge number always keeps changing dynamically. By programming and controlling the dynamic change interval of the topological charge, the difficulty of eavesdropping is further increased.

2. A method for anti-eavesdropping terahertz vortex beam communication based on dynamic topological charge, which is implemented based on the anti-eavesdropping terahertz vortex beam communication system based on dynamic topological charge according to claim 1, characterized in that: The steps include: (1) The useful signal is transmitted from the terahertz transmitter A through the horn antenna A, collimated by the terahertz lens A, and then input into the terahertz vortex beam generator A. After being reflected by the reflector, the signal enters the beam combining cube. (2) The terahertz transmitter B transmits the interference signal, which is then transmitted through the horn antenna B, collimated by the terahertz lens B, and then input into the terahertz vortex beam generator B. The interference signal is then combined with the useful signal in the beam combining cube for coaxial transmission. (3) After the useful signal and the interference signal are transmitted in free space for a certain distance, they are incident on the terahertz vortex beam generator C for dehelix; (4) The dehelixed beam is then filtered by the aperture, retaining only the part with a topological charge of 0. It is then converged to the horn antenna C through the terahertz lens C and detected and processed by the terahertz receiver.

3. According to claim 2, the anti-eavesdropping terahertz vortex beam communication method based on dynamic topological charge is characterized in that: In step (1) and step (2), the terahertz transmitter A and the terahertz transmitter B use a photonic transmitter or an electronic transmitter.

4. According to claim 2, the anti-eavesdropping terahertz vortex beam communication method based on dynamic topological charge is characterized in that: In step (1), the terahertz vortex beam generator A modulates the useful signal using a pre-agreed variation rule.

5. The anti-eavesdropping terahertz vortex beam communication method based on dynamic topological charge according to claim 4 is characterized in that: In step (2), the terahertz vortex beam generator B adopts a different change rule from that of the terahertz vortex beam generator A.

6. The anti-eavesdropping terahertz vortex beam communication method based on dynamic topological charge according to claim 5 is characterized in that: In step (3), the terahertz vortex beam generator C adopts a topological charge variation law that is conjugate with that of the terahertz vortex beam generator A, and can de-spiralize the vortex signal component carrying the useful signal into a beam with a topological charge equal to 0, while the vortex signal component carrying the interference signal is still a vortex beam with a spiral phase characteristic, thereby achieving separation of the useful signal and the interference signal.

7. The anti-eavesdropping terahertz vortex beam communication method based on dynamic topological charge according to claim 6 is characterized in that: In step (4), according to the characteristics of the vortex beam, the intensity distribution of the useful signal with a topological charge of 0 is a solid circle, while the intensity distribution of the interference signal with a topological charge of not 0 is a circular ring. The two are concentric and the inner diameter of the circular ring is larger than the diameter of the solid circle. The ring is filtered out using an aperture, and only the circle in the center is retained. In this way, the two signals can be separated.

8. The anti-eavesdropping terahertz vortex beam communication method based on dynamic topological charge according to claim 7 is characterized in that: The terahertz metasurface is manufactured based on the electrospray printing technology, which is realized by the electrospray printing equipment. The electrospray printing equipment includes a high-voltage power supply, a nozzle, and a collecting plate. The collecting plate is provided with a substrate for preparing the metasurface, and the nozzle is filled with liquid of the prepared metasurface material, and the internal air pressure is controlled by an air pressure control system. The collecting plate and the nozzle are respectively connected to two electrodes of the high-voltage power supply. When voltage is applied to the two, the liquid in the nozzle will be affected by the electric field force to form a curved liquid surface in a cone shape, which is called a Taylor cone. When the applied electric field force is large enough, the droplets will spray out jets or droplets from the tip of the Taylor cone. Photosensitive resin 9400 is used as the super surface material, and silicon dioxide is used as the base material.

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