A high-frequency wireless signal generator and its manufacturing method

Abstract

This invention discloses a high-frequency wireless signal generator, comprising a first substrate, a second substrate, a photo-aligned layer, spacers, and liquid crystal. The first and second substrates are disposed opposite to each other. The photo-aligned layer is disposed on the inner surface of the first substrate and the inner surface of the second substrate, respectively. The spacers are disposed between the photo-aligned layers and together with the first and second substrates form a filling space, in which the liquid crystal is housed. The photo-aligned layer is a photo-aligned film with a control pattern of radially continuously gradually changing directories, formed through multi-step overlapping ultraviolet polarization exposure. The control pattern of the photo-aligned film is used to control the radially continuously gradually changing directories of the liquid crystal molecules. This invention features wide-band applicability, miniaturization and easy integration, high efficiency and simplicity, low cost, and thinness, and has great application potential in terahertz mode multiplexing communication.

Description

Technical Field

[0001] This invention relates to the field of terahertz optoelectronics technology, and in particular to a high-frequency wireless signal generator and its fabrication method. Background Technology

[0002] Terahertz (THz) waves are electromagnetic waves with oscillation frequencies ranging from 0.1 to 10 THz. They are among the least understood and developed wavebands, possessing characteristics distinct from microwaves and visible light, and holding great potential. THz waves exhibit lower photon energy compared to X-rays, higher imaging resolution compared to ultrasound, higher frequencies compared to microwaves, and strong penetrability through many dielectric materials. These characteristics make THz technology attractive in a wide range of fields, including medical examinations, remote sensing, and high-speed wireless communication. Bessel beams, a typical non-diffractive beam, possess advantages such as good directionality, large focusing depth, and low transmission loss, and are widely used in optical imaging, processing, and particle manipulation. Vortex beams are another special type of electromagnetic field, exhibiting a helical phase distribution on the wavefront. They bring a new dimension to optical manipulation and can be quantified using topological charge, which refers to the number of times a wave rotates within a wavelength. Vortex beams have significant advantages in applications such as mode-division multiplexing communication and high-capacity parallel quantum computing. The combination of these two types of beams is expected to further enhance the level of THz photonics.

[0003] In recent years, numerous techniques have been developed for generating specific THz beams, such as specially designed phase plates, spatial light modulators, non-uniform birefringent crystals, and metasurface devices. Specific THz beams, including vortex, Airy, vector, and Bessel beams, have been demonstrated using these methods. However, current techniques have some limitations. They are either affected by design and manufacturing complexities or lack functional tunability and integration capabilities. Therefore, there is an urgent need to develop an efficient, tunable, and easily integrated method for realizing THz specific beam generators. Liquid crystals (LCs) possess wideband birefringence and excellent electro-optic tunability. Recently, high-transparency electrodes and high-quality alignment techniques for THz LC devices have been solved. In particular, LCs oriented by ultraviolet polarization exposure are well-suited for geometrically phase-controlled THz phase wavefronts. Simultaneously, LC-based mode converters offer the advantages of: half-wave conditions (maximizing mode conversion efficiency) can be electrically tuned over a wide bandwidth; and precise, free control of the local optical axis enables arbitrary wavefront operation.

[0004] Currently, methods for generating terahertz Bessel beams mainly include polymer conical lenses, metasurfaces with V-shaped antennas, and half-wave plates spliced ​​together with different optical axes. These methods suffer from drawbacks such as large device size, difficult fabrication, and low efficiency. There is an urgent need for a more efficient, simple, low-cost, and lightweight device to generate terahertz Bessel beams. Summary of the Invention

[0005] The purpose of this invention is to provide a high-frequency wireless signal generator and its manufacturing method, so as to solve the problems of large size, difficult processing, and low efficiency of the existing devices mentioned above.

[0006] To achieve the above objectives, embodiments of the present invention provide a high-frequency wireless signal generator, comprising a first substrate, a second substrate, a photo-alignment layer, spacers, and liquid crystal; the first substrate and the second substrate are disposed opposite to each other, the photo-alignment layer is disposed on the inner surface of the first substrate and the inner surface of the second substrate respectively, the spacers are disposed between the photo-alignment layers and together with the first substrate and the second substrate to form a filling space, and the liquid crystal is housed within the filling space; wherein, the photo-alignment layer is a photo-alignment film with a control pattern having a radially continuously gradually changing orientation vector formed by multiple steps of overlapping ultraviolet polarization exposure, and the control pattern of the photo-alignment film is used to control the radially continuously gradually changing orientation vector of the liquid crystal molecules in the liquid crystal.

[0007] In one embodiment, the photo-alignment layer is made of a thioazo dye.

[0008] In one embodiment, the spacer is a 400 μm thick polyester film.

[0009] In one embodiment, both the first substrate and the second substrate are quartz with a thickness of 500 μm.

[0010] In one embodiment, the liquid crystal is NJU-LDn-4, a liquid crystal material with an average birefringence of 0.31 in the range of 0.5-1.5THz.

[0011] This invention also provides a method for preparing a high-frequency wireless signal generator, comprising:

[0012] Provide a first substrate and a second substrate;

[0013] A light-controlled alignment layer is formed on one side of the first substrate and one side of the second substrate, respectively;

[0014] A spacer is provided between the side of the first substrate where the light-controlled alignment layer is provided and the side of the second substrate where the light-controlled alignment layer is provided, and then the substrate is encapsulated.

[0015] The light-controlled alignment layer is subjected to multi-step overlapping ultraviolet polarization exposure to form a control pattern with a radially continuously gradually changing director of the light-controlled alignment layer.

[0016] Liquid crystal is injected between the first substrate and the second substrate, and the control pattern of the photo-alignment film controls the molecular orientation vectors of the liquid crystal to be distributed in a continuously gradient radial direction.

[0017] In one embodiment, forming photo-alignment layers on one side of the first substrate and one side of the second substrate respectively specifically includes:

[0018] The alignment layer of the thiazo dye is spin-coated onto the first substrate and the second substrate, respectively, to form the photo-controlled alignment layer.

[0019] In one embodiment, the step of setting a spacer between the side of the first substrate where the light-controlled alignment layer is disposed and the side of the second substrate where the light-controlled alignment layer is disposed specifically includes:

[0020] The side of the first substrate with the light-controlled alignment layer and the side of the second substrate with the light-controlled alignment layer are separated by a 400μm thick polyester film to form a filling space.

[0021] In one embodiment, the process of injecting liquid crystal between the first substrate and the second substrate specifically includes:

[0022] The liquid crystal material NJU-LDn-4 with an average birefringence of 0.31 in the range of 0.5-1.5THz will be filled into the filling space.

[0023] In one embodiment, the step of performing multi-step overlapping ultraviolet polarization exposure on the photo-controlled alignment layer to form a control pattern with a radially continuously gradually varying directoric vector specifically includes:

[0024] A digital micromirror device based on dynamic micro-lithography is used to control the local azimuth angle of the fingertip of the light-controlled alignment layer to form a control pattern with a radially continuously gradually changing direction vector.

[0025] Compared with existing technologies, the high-frequency wireless signal generator provided in this invention has the characteristics of wide band applicability, miniaturization and easy integration, high efficiency and simplicity, low cost and thinness, and has great application potential in terahertz mode multiplexing communication and other fields. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of a high-frequency wireless signal generator provided in a certain embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the control pattern of the light-controlled alignment film provided in a certain embodiment of the present invention, showing that the direction vector of the liquid crystal molecules is continuously and gradually distributed in the radial direction.

[0029] Figure 3 This is a flowchart illustrating a method for preparing a high-frequency wireless signal generator according to a certain embodiment of the present invention;

[0030] Figure 4 This is a flowchart illustrating a method for preparing a high-frequency wireless signal generator according to a certain embodiment of the present invention;

[0031] Figure 5 This is a simulation diagram of a high-frequency wireless signal generator provided in a certain embodiment of the present invention;

[0032] Figure 6 This is a simulation diagram of a high-frequency wireless signal generator provided in another embodiment of the present invention;

[0033] Figure 7 This is a simulation diagram of a high-frequency wireless signal generator provided in another embodiment of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0036] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0037] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0038] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0039] Please see Figure 1 This invention provides a high-frequency wireless signal generator 100, which includes a first substrate 10, a second substrate 20, a light-controlled alignment layer 30, a spacer 40, and a liquid crystal 50.

[0040] The first substrate 10 and the second substrate 20 are disposed opposite to each other. The photo-alignment layers 30 are respectively disposed on the inner surfaces of the first substrate 10 and the second substrate 20. The spacers 40 are disposed between the photo-alignment layers 30 and together with the first substrate 10 and the second substrate 20 form a filling space. The liquid crystal 50 is housed in the filling space. The photo-alignment layer 30 is a photo-alignment film with a control pattern of radially continuously gradually changing orientation vectors formed by multi-step overlapping ultraviolet polarization exposure. The control pattern of the photo-alignment film is used to control the radially continuously gradually changing orientation vectors of the liquid crystal molecules of the liquid crystal 50.

[0041] In this embodiment of the invention, a THz Bessel vortex beam (BVB) generator combining helical phase and circular grating phase (i.e., the high-frequency wireless signal generator 100 of this invention) is proposed and designed using a geometric phase modulation method and a liquid crystal 50. The non-diffraction propagation characteristics and orbital angular momentum modes of the transmitted wavefront are numerically simulated. The performance of the THz BVB generator is characterized using a scanning near-field THz microscope (SNTM). The characteristics of the THz BVB generated by the LC geometric phase unit are consistent with the simulation, showing high mode conversion efficiency in the broadband. Here, geometric phase, i.e., Pancharatnam-Berry phase, is used in the design of the THz BVB generator. It originates from photon spin-orbit interaction and can be manipulated by directional control through anisotropic media such as LCs and metasurface harmonic oscillators. For an LC waveplate with an orientation angle α, its Jones matrix can be expressed as:

[0042]

[0043] Where R is the rotation matrix, ζ = πδnd / λ is half of the phase retardation (δn, d, and λ are the LC birefringence, the 50-layer thickness of the liquid crystal, and the wavelength, respectively), and I is the identity matrix. For circularly polarized light, the normalized Jones vectors are χ(+) = (1+i)T / left circular polarization (LCP) and χ(-) = (1-i)T / circular polarization (RCP). When a circularly polarized wave is incident, the output wave is described as:

[0044]

[0045] For an LCP incident wave, the output wave is split into two parts. One is the remaining LCP component, without additional phase modulation. The other is the converted RCP component, which has a phase factor of exp(i²α) that depends only on α. ​​The reverse is also true.

[0046] The designed phase diagram consists of two parts: the vortex phase and the circular grating phase. The final phase... Satisfy the following equation:

[0047]

[0048] The first term on the right is the vortex term, where m is the topological charge. The second term describes the phase of the circular grating, where Λ is the periodicity of 0-2π along radius r. It can act as an axonocone to generate a zero-order Bessel beam. The non-diffraction distance L of the zero-order Bessel beam can be obtained as:

[0049]

[0050] Where R is the radius of the entire phase plate. In a specific embodiment, as a proof-of-concept demonstration, such as... Figure 2 As shown in (a) and (b), a vortex step phase of m = 2 and a circular grating phase of Λ = 1728 μm were designed. Besides the phase distribution diagram, the LC layer thickness is another important factor determining the polarization conversion ratio (PCR). As shown in equation (2), PCR = sinζ 2 In other words, PCR is maximized when d satisfies the half-wave condition. Deviating from the half-wave condition will lead to a decrease in PCR. Here, the thickness d of the 50-layer liquid crystal is set to 400 μm to satisfy the half-wave condition at 1.2 THz.

[0051] like Figure 1 As shown, Figure 1This is a cross-sectional schematic diagram of a high-frequency wireless signal generator 100 according to an embodiment of the present invention. Specifically, the high-frequency wireless signal generator 100 includes upper and lower transparent substrates, a light-controlled alignment layer 30 attached to the inner surface of the transparent substrates, and a liquid crystal 50 layer in the middle. Spacers 40 are used to support the upper and lower substrates to form the filling space of the liquid crystal 50. The orientation vector distribution of the liquid crystal molecules in the liquid crystal 50 is as follows: Figure 2 As shown in (c) Figure 2 (d) is a photograph of the LC sample made under a cross-polarizing microscope (indicated by two arrows), with a scale bar of 1 mm, to form the phase template required to generate Bessel vortex light.

[0052] The THz LC BVB generator proposed in this embodiment has the following advantages: Its principle is based on the geometric phase modulation of anisotropic waveplates. The phase diagram is a combination of vortex phase and circular grating. The resulting BVB exhibits characteristics of both vortex and Bessel beams. The BVB possesses the topological properties described by OAM and remarkable non-diffraction-induced good directivity. These unique properties make the BVB ideal for detection, micromanipulation, and mode-division multiplexing-based communications. The geometric phase mechanism and wideband birefringence of LCs make them suitable for broadband applications. Furthermore, the half-wave condition determines the maximum mode conversion efficiency, and combined with the tunability of LCs induced by external fields, tunable and even switchable mode converters are possible. Due to the high resolution of directional distribution control and the flexibility of wavefront operation, it is reasonable to expect free mode coding. Further integration of this geometric phase LC element with other components will greatly expand the functionality of THz elements, even enabling active dispersion operation and spin-multiplexed THz photonics.

[0053] Therefore, compared with the prior art, the high-frequency wireless signal generator 100 provided in this embodiment of the invention has the characteristics of wide band applicability, miniaturization and easy integration, high efficiency and simplicity, low cost and thinness, and has great application potential in terahertz mode multiplexing communication and other fields.

[0054] In one embodiment, the photo-alignment layer 30 is made of a thioazo dye.

[0055] In one embodiment, the spacer 40 is a 400 μm thick polyester film.

[0056] In one embodiment, both the first substrate 10 and the second substrate 20 are quartz with a thickness of 500 μm.

[0057] In one embodiment, the liquid crystal 50 is a liquid crystal material NJU-LDn-4 with an average birefringence of 0.31 in the range of 0.5-1.5THz.

[0058] In this embodiment of the invention, NJU-LDn-4 is a highly birefringent liquid crystal material, which has a birefringence of 0.3 near 1THz.

[0059] Please see Figure 3 and Figure 4 This invention also provides a method for manufacturing a high-frequency wireless signal generator 100, comprising the following steps:

[0060] S120, providing a first substrate 10 and a second substrate 20;

[0061] S121. A light-controlled alignment layer 30 is formed on one side of the first substrate 10 and one side of the second substrate 20, respectively.

[0062] S122. A spacer 40 is provided between the side of the first substrate 10 where the light-controlled alignment layer 30 is provided and the side of the second substrate 20 where the light-controlled alignment layer 30 is provided, and then the substrate is encapsulated.

[0063] S123. Perform multi-step overlapping ultraviolet polarization exposure on the light-controlled alignment layer 30 to form a control pattern with a radially continuously gradually changing distribution of the director.

[0064] S124. Liquid crystal 50 is injected between the first substrate 10 and the second substrate 20, and the control pattern of the photo-alignment film controls the molecular orientation vector of the liquid crystal 50 to be continuously and gradually distributed in the radial direction.

[0065] In one embodiment, step S121, which involves forming a light-controlled alignment layer 30 on one side of the first substrate 10 and one side of the second substrate 20, specifically includes the following steps:

[0066] The alignment layer of the thioazo dye is spin-coated onto the first substrate 10 and the second substrate 20 respectively to form the photo-alignment layer 30.

[0067] In one embodiment, step S122, which involves setting a spacer 40 between the side of the first substrate 10 where the light-controlled alignment layer 30 is disposed and the side of the second substrate 20 where the light-controlled alignment layer 30 is disposed, specifically includes the following steps:

[0068] The side of the first substrate 10 with the light-controlled alignment layer 30 and the side of the second substrate 20 with the light-controlled alignment layer 30 are separated by a 400μm thick polyester film to form a filling space.

[0069] In one embodiment, step S124, which involves injecting liquid crystal 50 between the first substrate 10 and the second substrate 20, specifically includes the following steps:

[0070] The liquid crystal material NJU-LDn-4 with an average birefringence of 0.31 in the range of 0.5-1.5THz will be filled into the filling space.

[0071] In one embodiment, step S123, which involves performing multi-step overlapping ultraviolet polarization exposure on the photo-alignment layer 30 to form a control pattern with a radially continuously gradually varying direction vector, specifically includes the following steps:

[0072] A digital micromirror device based on dynamic micro-lithography is used to control the local azimuth angle of the fingertip of the light-controlled alignment layer 30 to form a control pattern with a radially continuously gradually changing directional vector.

[0073] In one embodiment, before step S121, which involves forming the photo-alignment layer 30 on one side of the first substrate 10 and one side of the second substrate 20, the following step is further included:

[0074] The first substrate 10 and the second substrate 20 are ultrasonically cleaned.

[0075] In one specific embodiment, the manufacturing process of the THz LC BVB generator is as follows: Figure 4 As shown. Two substrates are 500 μm thick quartz. After ultrasonic cleaning, an alignment layer of a thioazo dye (SD1, Dainippon Ink and Chemicals Inc., Chiba, Japan) is spin-coated onto the substrates. The two substrates are then assembled, separated by a 400 μm thick polyester film to form a liquid crystal 50 filling space. The local azimuth angle of the LC finger tip is controlled using a digital micromirror device based on dynamic micro-lithography, resulting in the following... Figure 2 (c) shows the desired phase diagram. After filling the gap between the two substrates with liquid crystal material NJU-LDn-4, which has an average birefringence of 0.31 (0.5-1.5 THz), the resulting LC orientation ( Figure 2 (d)) It matches the design very well.

[0076] To verify the performance of the high-frequency wireless signal generator 100 designed in this embodiment of the invention, a numerical simulation of the THz LC BVB generator was performed using the commercial simulation software Lumerical FDTD Solutions. Figure 5 (c) The phase diagram was simulated. A simulation model was built on the xy plane composed of many small LC pixels. Each pixel was set to 200μm × 200μm × 400μm (x × y × z). The liquid crystal 50 was set as a diagonal dielectric material, n o =1.60 (diagonal elements x and y) and n e= 1.91 (diagonal element zz). The spatial distribution of the LC pointer direction is set by the LC orientation module. The plane THz wave is incident along the z-axis. Figure 5 (a) shows the simulated THz intensity distribution in the xz plane at 1.2 THz when the LCP wave is incident, with a non-diffraction distance greater than 20 mm. The central dark region corresponds to the singularity of the vortex beam. Figure 5 (b) and Figure 5 (c) A donut-like intensity distribution was observed in the xy-plane. Due to far-field diffraction, the intensity of the central ring decays exponentially along the radius. The diameter of the central ring at z = 20 mm is essentially the same as that at z = 5 mm, verifying the non-diffraction characteristics of the BVB. Furthermore, the phase distribution in the xy-plane at 1.2 THz was simulated. Two alternating 0-2π centers represent the topological kernel number m = 2 of the OAM.

[0077] This invention utilizes an SNTM device (Terahertz Photonics Co., Ltd., China) to perform THz wave generation and detection based on a light-guided antenna, enabling the characterization of the THz BVB generator's performance. In this device, a scanning probe fixed to a motorized stage records the Ex field in the xy-plane with a step size of 0.2 mm. The sample moves along the z-axis with a step size of 0.5 mm to capture the Ex field in the xz-plane. The measured THz intensity distribution at 1.2 THz in the xz-plane is shown below. Figure 6 As shown in (a). Figure 6 (b)-6(e) show the THz intensity and phase distributions measured at 1.2 THz at z = 5 mm, 10 mm, 15 mm, and 20 mm, respectively. The distinctive donut-shaped intensity profile and vortex phase are clearly presented. Although the diameter of the central ring gradually increases, the results agree well with the simulation, indicating no diffraction. To quantitatively evaluate the beam profile on the transmission section, Figure 6 (b) The intensity along the x-axis and y-axis is Figure 6 The plot is shown in (f). The intensity along both the x and y axes shows a decrease at r = 0 mm, followed by two peaks. Exponentially decaying side lobes are also observed in the transmission profile. All spin-transformed waves carry the designed phase; therefore, the mode conversion efficiency is determined by PCR. The frequency dependence of PCR is as follows: Figure 6 As shown in (g). The PCR close to 1 at 1.2 THz is due to optimized half-wave conditions.

[0078] Due to frequency-independent geometric phase modulation, the LC BVB generator operates in a wideband environment. Embodiments of the invention characterize their performance at 1.1 and 1.4 THz, as shown below. Figure 7 (c) and Figure 7 As shown in (d), the intensity distribution in the xz plane ( Figure 7 (a) and Figure 7(b) indicates that BVB has good non-diffraction characteristics. The intensity and phase distribution in the xy plane are very similar to those at 1.2 THz, verifying its capability in broadband THz wave processing.

[0079] In summary, this invention presents and demonstrates a high-frequency wireless signal generator 100 (i.e., a THz BVB generator) based on geometric phase modulation of a specially designed non-uniform LC waveplate, which combines helical phase and circular grating phase. The generated BVB carries a topological charge and exhibits good directivity. These characteristics make it suitable for advanced THz applications. Its broadband operation has been verified, and its electrical tuning efficiency is expected. The proposed generator can be further integrated with peripheral devices, which may lead to upgrades to existing hardware.

[0080] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A high-frequency wireless signal generator, characterized in that, The phase diagram designed using geometric phase modulation consists of two parts: a vortex phase and a circular grating phase; it includes a first substrate, a second substrate, a photo-aligned layer, spacers, and liquid crystal. The first substrate and the second substrate are disposed opposite to each other. The photo-alignment layers are respectively disposed on the inner surfaces of the first substrate and the second substrate. The spacers are disposed between the photo-alignment layers and together with the first substrate and the second substrate form a filling space. The liquid crystal is housed in the filling space. The photo-alignment layers are photo-alignment films with a control pattern of radially continuously gradually distributed directories formed by multi-step overlapping ultraviolet polarization exposure. The control pattern of the photo-alignment film is used to control the radially continuously gradually distributed directories of the liquid crystal molecules to form the phase template required to generate Bessel vortex light. The thickness of the liquid crystal is set to 400 μm to meet the half-wave condition at 1.2 THz. The liquid crystal is NJU-LDn-4, a liquid crystal material with an average birefringence of 0.31 in the range of 0.5-1.5 THz. The control pattern is formed by controlling the local azimuth angle of the fingertips of the photo-alignment layers using a digital micromirror device based on dynamic micro-planing printing.

2. The high-frequency wireless signal generator according to claim 1, characterized in that, The photo-alignment layer is made of thioazo dye.

3. The high-frequency wireless signal generator according to claim 1, characterized in that, The spacer is a 400 μm thick polyester film.

4. The high-frequency wireless signal generator according to claim 1, characterized in that, Both the first substrate and the second substrate are quartz with a thickness of 500 μm.

5. A method for manufacturing a high-frequency wireless signal generator, characterized in that, Employing geometric phase modulation, the designed phase diagram consists of two parts: a vortex phase and a circular grating phase; including: Provide a first substrate and a second substrate; A light-controlled alignment layer is formed on one side of the first substrate and one side of the second substrate, respectively; A spacer is provided between the side of the first substrate with the light-controlled alignment layer and the side of the second substrate with the light-controlled alignment layer, and the substrate is then encapsulated. The spacer, together with the first substrate and the second substrate, forms a filling space. The light-controlled alignment layer is subjected to multi-step overlapping ultraviolet polarization exposure to form a control pattern with a radially continuously gradually changing director of the light-controlled alignment layer. Liquid crystal is injected between the first substrate and the second substrate. The control pattern of the photo-alignment film controls the molecular orientation vector of the liquid crystal to be distributed in a continuous and gradual radial direction to form the phase template required to generate Bessel vortex light. The thickness of the liquid crystal is set to 400 μm to satisfy the half-wave condition at 1.2 THz. The process of injecting liquid crystal between the first substrate and the second substrate specifically includes: The liquid crystal material NJU-LDn-4 with an average birefringence of 0.31 in the range of 0.5-1.5 THz will be filled into the filling space; The step of performing multi-step overlapping ultraviolet polarization exposure on the photo-controlled alignment layer to form a control pattern with a radially continuously gradually varying direction vector specifically includes: A digital micromirror device based on dynamic micro-lithography is used to control the local azimuth angle of the fingertip of the light-controlled alignment layer to form a control pattern with a radially continuously gradually changing direction vector.

6. The preparation method according to claim 5, characterized in that, The formation of light-controlled alignment layers on one side of the first substrate and one side of the second substrate, respectively, specifically includes: The alignment layer of the thiazo dye is spin-coated onto the first substrate and the second substrate, respectively, to form the photo-controlled alignment layer.

7. The preparation method according to claim 5, characterized in that, The step of setting a spacer between the side of the first substrate with the light-controlled alignment layer and the side of the second substrate with the light-controlled alignment layer specifically includes: The side of the first substrate with the light-controlled alignment layer and the side of the second substrate with the light-controlled alignment layer are separated by a 400 μm thick polyester film to form a filling space.

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