CN111999939B

CN111999939B - High-frequency wireless signal generator and preparation method thereof

Info

Publication number: CN111999939B
Application number: CN202010756240.XA
Authority: CN
Inventors: 李小明; 徐振华
Original assignee: Guangzhou Railway Polytechnic
Current assignee: Guangzhou Railway Polytechnic
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2025-10-31
Anticipated expiration: 2040-07-30
Also published as: CN111999939A

Abstract

The invention discloses a high-frequency wireless signal generator, which comprises a first substrate, a second substrate, photo-alignment layers, spacers and liquid crystals, wherein the first substrate and the second substrate are arranged oppositely, the photo-alignment layers are respectively arranged on the inner surface of the first substrate and the inner surface of the second substrate, the spacers are arranged between the photo-alignment layers, and form a filling space together with the first substrate and the second substrate, the liquid crystals are contained in the filling space, the photo-alignment layers are photo-alignment films which are formed through multi-step overlapping ultraviolet polarization exposure and have control patterns with directors continuously and gradually distributed in the radial direction, and the control patterns of the photo-alignment films are used for controlling the liquid crystal molecule directors of the liquid crystals to continuously and gradually distributed in the radial direction. The invention has the characteristics of wide band application, miniaturization, easy integration, high efficiency, simplicity, low cost, light weight and thin design, and has great application potential in the aspects of terahertz mode multiplexing communication and the like.

Description

High-frequency wireless signal generator and preparation method thereof

Technical Field

The invention relates to the technical field of terahertz photoelectrons, in particular to a high-frequency wireless signal generator and a preparation method thereof.

Background

Terahertz (THz) waves are electromagnetic waves with an oscillation frequency of 0.1-10 THz. It is the least understood and developed band, has different characteristics from microwaves and visible light, and has great potential. THz waves have lower photon energies relative to x-rays, higher imaging resolution relative to ultrasound waves, higher frequencies relative to microwaves, and greater penetration of many dielectric materials. The characteristics make THz technology attractive in the wide fields of medical physical examination, remote sensing, high-speed wireless communication and the like. Bessel beam (Bessel beam) is a typical non-diffracted beam, has the advantages of good directivity, large focusing depth and low transmission loss, and is widely applied to optical imaging, processing and particle manipulation. A vortex beam is another special electromagnetic field whose wavefront exhibits a helical phase distribution. It brings a new dimension for optical manipulation, and can be quantitatively described by topology load, which refers to the rotation times of waves in a wavelength. Vortex beams have significant advantages in applications such as mode division multiplexing communications and high-capacity parallel quantum computing. The combination of the two beams is expected to further improve the level of THz photonics.

Over the past few years, many techniques have been developed for generating specific THz beams, such as specially designed phase plates, spatial light modulators, non-uniform birefringent crystals, and super-surface devices. By these methods, specific THz beams including vortex, eiri, vector and bessel beams have been demonstrated. However, the current technology has some disadvantages. They are either affected by design and manufacturing complexity or lack functional adjustability and integration capability. Therefore, there is an urgent need to develop an efficient, tunable and easy-to-integrate method to implement THz specific beam generators. The liquid crystal has wide-band birefringence and excellent electro-optic adjustability. Recently, both high transparency electrodes and high quality orientation techniques of THz LC devices have been solved. In particular, LCs with ultraviolet polarized exposure orientation are well suited for geometrically phased control of THz phase wavefronts. Meanwhile, the LC-based mode converter has the advantages that half-wave conditions (mode conversion efficiency is maximized) can be electrically tuned in a broadband, and local optical axes can be precisely and freely controlled to realize any wavefront operation.

The current method for generating terahertz Bessel beams mainly comprises a polymer conical lens, an ultra-structured surface designed with a V-shaped antenna, half wave plates spliced in different optical axis directions and the like. These methods have drawbacks in that the device is large, difficult to process, and inefficient, and there is an urgent need for a device that is efficient, simple, low-cost, and lightweight to produce terahertz bessel beams.

Disclosure of Invention

The invention aims to provide a high-frequency wireless signal generator and a preparation method thereof, which are used for solving the problems of large size, difficult processing, low efficiency and the like of the prior devices.

In order to achieve the above object, the embodiment of the invention provides a high-frequency wireless signal generator, which comprises a first substrate, a second substrate, photo-alignment layers, spacers and liquid crystals, wherein the first substrate and the second substrate are arranged opposite to each other, the photo-alignment layers are respectively arranged on the inner surfaces of the first substrate and the second substrate, the spacers are arranged between the photo-alignment layers, and form a filling space together with the first substrate and the second substrate, the liquid crystals are accommodated in the filling space, the photo-alignment layers are photo-alignment films which are formed through multi-step overlapping ultraviolet polarization exposure and have control patterns with directors which are continuously and gradually distributed in the radial direction, and the control patterns of the photo-alignment films are used for controlling the liquid crystal molecular directors of the liquid crystals to continuously and gradually distribute in the radial direction.

In one embodiment, the photoalignment layer is made of a sulfur azo dye.

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

In one embodiment, the first substrate and the second substrate are each 500 μm thick quartz.

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

The embodiment of the invention also provides a preparation method of the high-frequency wireless signal generator, which comprises the following steps:

Providing a first substrate and a second substrate;

forming a photo-alignment layer on one side of the first substrate and one side of the second substrate, respectively;

Arranging spacers on one surface of the first substrate, on which the photo-alignment layer is arranged, and one surface of the second substrate, on which the photo-alignment layer is arranged, and packaging;

Performing multi-step overlapping ultraviolet polarization exposure on the photo-alignment layer so as to enable the photo-alignment layer to form a control pattern with directors continuously and gradually distributed in the radial direction;

And filling liquid crystal between the first substrate and the second substrate, wherein the control pattern of the photo-alignment film controls the molecular directors of the liquid crystal to continuously and gradually distribute in the radial direction.

In one embodiment, the forming the photoalignment layer on one side of the first substrate and one side of the second substrate respectively specifically includes:

spin-coating alignment layers of sulfur azo dyes onto the first and second substrates, respectively, to form the photoalignment layers.

In one embodiment, the disposing a spacer between the surface of the first substrate on which the photoalignment layer is disposed and the surface of the second substrate on which the photoalignment layer is disposed specifically includes:

And the surface of the first substrate provided with the photo-alignment layer is separated from the surface of the second substrate provided with the photo-alignment layer by a polyester film with the thickness of 400 mu m, so as to form a filling space.

In one embodiment, the filling liquid crystal between the first substrate and the second substrate specifically includes:

A liquid crystal material NJU-LDn-4 with an average birefringence of 0.31 in the range of 0.5-1.5THz is poured into the filling space.

In one embodiment, the performing multi-step overlapping ultraviolet polarization exposure on the photoalignment layer to form a control pattern with a continuously graded director distribution in a radial direction on the photoalignment layer specifically includes:

And controlling the local azimuth angle of the finger end of the photo-alignment layer by adopting a digital micro-mirror device based on dynamic micro-lithography to form a control pattern with a continuously gradual distribution of directors in the radial direction.

Compared with the prior art, the high-frequency wireless signal generator provided by the embodiment of the invention has the characteristics of wide band application, miniaturization, easiness in integration, high efficiency, simplicity, low cost, thinness and thinness, and has great application potential in the aspects of terahertz mode multiplexing communication and the like.

Drawings

In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of a high-frequency wireless signal generator according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a control pattern for a photoalignment film according to an embodiment of the present invention to control a continuously graded distribution of directors of liquid crystal molecules in a radial direction;

Fig. 3 is a schematic flow chart of a method for manufacturing a high-frequency wireless signal generator according to an embodiment of the present invention;

fig. 4 is a flow chart of a method for manufacturing a high-frequency wireless signal generator according to an embodiment of the present invention;

FIG. 5 is a schematic diagram illustrating a simulation of a high frequency wireless signal generator according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a simulation of a high frequency wireless signal generator according to another embodiment of the present invention;

fig. 7 is a schematic diagram of a simulation of a high frequency wireless signal generator according to another embodiment of the present invention.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

It should be understood that the step numbers used herein are for convenience of description only and are not limiting as to the order in which the steps are performed.

It is to be understood that the terminology used in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of 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 as well, unless the context clearly indicates otherwise.

The terms "comprises" and "comprising" indicate the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The term "and/or" refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.

Referring to fig. 1, an embodiment of the present invention provides a high frequency wireless signal generator 100, which includes a first substrate 10, a second substrate 20, an optically-oriented layer 30, spacers 40 and a liquid crystal 50.

The first substrate 10 and the second substrate 20 are disposed opposite to each other, the photo-alignment layers 30 are disposed on the inner surface of the first substrate 10 and the inner surface of the second substrate 20, the spacers 40 are disposed between the photo-alignment layers 30, and form a filling space together with the first substrate 10 and the second substrate 20, and the liquid crystal 50 is contained in the filling space, wherein the photo-alignment layers 30 are photo-alignment films having control patterns with directors continuously graded in a radial direction, and the control patterns of the photo-alignment films are used for controlling the liquid crystal molecular directors of the liquid crystal 50 to continuously graded in a radial direction.

In the embodiment of the present invention, a THz Bessel Vortex Beam (BVB) generator (i.e., the high-frequency wireless signal generator 100 of the present invention) combining a spiral phase with a circular grating phase is provided, and a geometric phase modulation method is adopted to design the device by using the liquid crystal 50. Numerical simulations were performed on the non-diffractive propagation characteristics and the orbital angular momentum modes of the transmitted wavefront. The performance of the THz BVB generator was characterized using a scanning near field THz microscope (SNTM). The THz BVB produced by the LC geometry phase cell has characteristics consistent with the simulation, showing higher mode conversion efficiency in the broadband. Wherein the design of the THz BVB generator is performed here using a geometrical phase, i.e. a Pancharatnam-Berry phase. It originates from photon spin orbital interactions and can be manipulated by directional control of anisotropic media such as LCs and super-surface resonators. For an LC waveplate with an orientation angle α, its jones matrix can be expressed as:

Where R is the rotation matrix, ζ=pi δnd/λ is half the amount of phase retardation (δn, d and λ are LC birefringence, liquid crystal 50 layer thickness and wavelength, respectively), and I is the identity matrix. For circularly polarized light, normalized jones vectors are χ (+) = (1+i) T/Left Circularly Polarized (LCP) and χ (-) = (1-i) T/circularly polarized (RCP). When a circularly polarized wave is incident, the output wave is described as:

For LCP incident waves, the output wave is split into two parts. One is the remaining LCP component, with no additional phase modulation. The other is the converted RCP component, which has a phase factor of exp (i2α) that is related to α only. And vice versa.

The designed phase diagram consists of two parts, namely vortex phase and circular grating phase. Final phaseThe following equation is satisfied:

the first term on the right is the vortex term, where m is the topological charge. The second term describes the phase of a circular grating, where Λ is the period alternating along the radius r from 0-2pi. It can act as an axicon to generate a zero order bessel beam. The non-diffraction distance L from which the zero-order bessel beam can be obtained is:

Where R is the radius of the entire phase plate. In a specific embodiment, as a proof of concept demonstration, as shown in fig. 2 (a) and (b), a vortex order phase of m=2 and a circular grating phase Λ=1728 μm is designed. In addition to the phase profile, LC layer thickness is another important factor in determining the polarization conversion (polarization conversion ratio, PCR). As in equation (2), pcr=sin ζ ², that is, PCR is maximized when d satisfies the half-wave condition. Deviations from half-wave conditions will lead to a decrease in PCR. Here, the thickness d of the liquid crystal 50 layer is set to 400 μm, satisfying the half-wave condition at 1.2 THz.

Referring to fig. 1, fig. 1 is a schematic cross-sectional view of a high-frequency wireless signal generator 100 according to an embodiment of the invention. Specifically, the high-frequency wireless signal generator 100 includes upper and lower transparent substrates, a photo-alignment layer 30 attached to the inner surface of the transparent substrates, and an intermediate liquid crystal layer 50, and spacers 40 for supporting the upper and lower substrates to form a filling space for the liquid crystal layer 50. The director distribution of the liquid crystal molecules in the liquid crystal 50 is shown in fig. 2 (c), and fig. 2 (d) is a photograph (indicated by two arrows) of an LC sample fabricated under crossed polarizers, with a scale of 1mm, to form a phase template required to generate bessel vortex rotation.

The THz LC BVB generator proposed by this embodiment has the advantage that the principle is geometrical phase modulation of the anisotropic wave plate. The phase diagram is a combination of vortex phase and circular grating. The resulting BVB has the characteristics of a vortex and Bessel beam. BVB has the topology described by OAM and significant non-diffraction induced good directionality. These unique properties make BVB an ideal choice for probing, micro-operation, and mode division multiplexing based communications. The geometric phase mechanism and broadband birefringence characteristics of LCs make them useful over a wide band. In addition, the half-wave condition determines the maximum mode conversion efficiency, and the LCs caused by the external field is adjustable, so that an adjustable and even switchable mode converter is possible. Due to the high resolution of the directivity distribution control and the flexibility of the wavefront operation, it is reasonably desirable to freely perform various mode encodings. Further integrating the geometric phase LC element with components greatly expands the functions of the THz element, and even can realize active dispersion operation and spin multiplexing THz photonics.

Therefore, compared with the prior art, the high-frequency wireless signal generator 100 provided by the embodiment of the invention has the characteristics of wide band application, miniaturization, easy integration, high efficiency, simplicity, low cost, light weight and thin performance, and has great application potential in the aspects of terahertz mode multiplexing communication and the like.

In one embodiment, the photoalignment layer 30 is made of a sulfur azo dye.

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

In one embodiment, the first substrate 10 and the second substrate 20 are each 500 μm thick quartz.

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

In the embodiment of the invention, NJU-LDn-4 is a large-birefringence liquid crystal material, and the birefringence index of the material reaches 0.3 near 1 THz.

Referring to fig. 3 and 4, the embodiment of the invention further provides a method for preparing the high-frequency wireless signal generator 100, which comprises the following steps:

s120, providing a first substrate 10 and a second substrate 20;

S121 forming a photoalignment layer 30 on one side of the first substrate 10 and one side of the second substrate 20, respectively;

S122, arranging a spacer 40 on the surface of the first substrate 10, on which the photo-alignment layer 30 is arranged, and the surface of the second substrate 20, on which the photo-alignment layer 30 is arranged, and packaging;

s123, performing multi-step overlapped ultraviolet polarization exposure on the photoalignment layer 30 so as to enable the photoalignment layer 30 to form a control pattern with directors continuously and gradually distributed in the radial direction;

s124, filling liquid crystal 50 between the first substrate 10 and the second substrate 20, wherein the control pattern of the photo-alignment film controls the molecular directors of the liquid crystal 50 to continuously and gradually distribute in the radial direction.

In one embodiment, the step S121 forms the photoalignment layer 30 on one side of the first substrate 10 and one side of the second substrate 20, and specifically includes the following steps:

Alignment layers of sulfur azo dyes are spin-coated onto the first substrate 10 and the second substrate 20, respectively, to form the photoalignment layer 30.

In one embodiment, the step S122, where the spacer 40 is disposed between the surface of the first substrate 10 on which the photoalignment layer 30 is disposed and the surface of the second substrate 20 on which the photoalignment layer 30 is disposed, specifically includes the following steps:

The side of the first substrate 10 on which the photoalignment layer 30 is disposed and the side of the second substrate 20 on which the photoalignment layer 30 is disposed are separated by a 400 μm thick polyester film to form a filling space.

In one embodiment, the step S124 of filling the liquid crystal 50 between the first substrate 10 and the second substrate 20 specifically includes the following steps:

In one embodiment, the step S123 performs multi-step overlapping uv polarization exposure on the photoalignment layer 30, so that the photoalignment layer 30 forms a control pattern with a continuously graded director distribution in a radial direction, and specifically includes the following steps:

The local azimuth angle of the finger tip of the photo-alignment layer 30 is controlled using a digital micromirror device based on dynamic microlithography to form a control pattern with a continuously graded radial director profile.

In one embodiment, before forming the photoalignment layer 30 on the side of the first substrate 10 and the side of the second substrate 20 in the step S121, the method further includes the following steps:

the first substrate 10 and the second substrate 20 are ultrasonically cleaned.

In one embodiment, the THz LC BVB generator is fabricated as shown in fig. 4. Both substrates were 500 μm thick quartz. After ultrasonic cleaning, an alignment layer of sulfur azo dye (SD 1, dainpon INK AND CHEMICALS inc., chiba, japan) was spin-coated onto the substrate. After that, the two substrates were assembled, and a liquid crystal 50 filling space was formed by separating them with a 400 μm thick polyester film. The local azimuth of the LC finger is controlled using a digital micromirror device based on dynamic microlithography to obtain the desired phase diagram as shown in fig. 2 (c). After filling a liquid crystal material NJU-LDn-4 having an average birefringence of 0.31 (0.5-1.5 THz) into the gap between the two substrates, the resulting LC alignment (FIG. 2 (d)) was well-matched to the design.

To verify the performance of the high frequency wireless signal generator 100 for which embodiments of the present invention were designed, embodiments of the present invention used commercial simulation software Lumerical FDTD Solutions to numerically simulate the THz LC BVB generator. Simulations were performed based on the phase diagram of fig. 5 (c). A simulation model is built on the xy plane, which consists of many small LC pixels. Is set to 200 μm by 400 μm (x y x z) per pixel. The liquid crystal 50 is provided as one diagonal dielectric material, n _o =1.60 (diagonal elements xx and yy) and n _e =1.91 (diagonal element zz). The spatial distribution of LC director directions is set by the LC orientation module. The planar THz wave is incident along the z-axis. Fig. 5 (a) is a simulated THz intensity distribution of xz plane at 1.2THz with non-diffraction distance greater than 20mm at LCP wave incidence. The central dark region corresponds to the singularity of the vortex beam. Fig. 5 (b) and 5 (c) are intensity distributions in the xy plane that are observed like a doughnut. The intensity of the center ring decays exponentially along the radius due to the effects of far field diffraction. The diameter of the central ring at z=20 mm was substantially the same as the diameter at z=5 mm, verifying the non-diffractive properties of BVB. Furthermore, the phase distribution of the xy plane at 1.2THz was also simulated. The two centers 0-2 pi alternately show the topology core number m=2 of OAM.

The embodiment of the invention utilizes SNTM equipment (terahertz photonics limited company, china) to generate and detect THz waves based on the photoconductive antenna, and can characterize the performance of the THz BVB generator. In this device, the Ex field in the x-y plane is recorded with a scanning probe fixed on a motorized stage, with a step size of 0.2mm. The sample is moved along the z-axis, with a step size of 0.5mm, capturing the Ex field in the x-z plane. The measured THz intensity distribution at 1.2THz in the x-z plane is shown in fig. 6 (a). Fig. 6 (b) -6 (e) are THz intensity and phase distribution measured at 1.2THz at z=5 mm, 10mm, 15mm and 20mm, respectively. The distinctive doughnut-type intensity profile and vortex phase are clearly presented. Although the diameter of the center ring gradually increased, the results were better matched with the simulations, indicating no diffraction. To quantitatively evaluate the beam profile on the transmission section, the intensities along the x-axis and the y-axis in fig. 6 (b) are plotted in fig. 6 (f). There is a drop in intensity along both the x-axis and the y-axis at r=0 mm, with two peaks beside. Exponentially decaying side lobes are also observed in the transmission profile. All spin-converted waves have a designed phase, and thus, the mode conversion efficiency is determined by PCR. The dependence of PCR on frequency is shown in FIG. 6 (g). The PCR approaching 1 at 1.2THz is due to optimized half-wave conditions.

The LC BVB generator operates in broadband due to the frequency independent geometric phase modulation. The performance of the inventive examples was characterized at 1.1 and 1.4THz as shown in fig. 7 (c) and 7 (d). The intensity distribution in the xz plane (fig. 7 (a) and fig. 7 (b)) shows that BVB has good non-diffractive properties. The xy plane light intensity and phase distribution is very similar to that at 1.2THz, verifying its ability to process broadband THz waves.

In summary, embodiments of the present invention propose and demonstrate a high frequency wireless signal generator 100 (i.e., THz BVB generator) based on geometric phase modulation of a specially designed non-uniform LC waveplate, which combines spiral phase and circular grating phase. The generated BVB has topological charges and good directivity. These features make it suitable for advanced THz applications. Its broadband operation capability is verified and its electrical tuning efficiency can be expected. The proposed period may be further integrated with the meta-device, which may lead to upgrades of existing hardware devices.

While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the invention, such changes and modifications are also intended to be within the scope of the invention.

Claims

1. A high-frequency wireless signal generator, characterized in that it employs geometric phase modulation, and the designed phase diagram 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 a 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, wherein the optically controlled alignment layer is made of a thioazo dye.

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

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

5. A method for fabricating a high-frequency wireless signal generator, characterized in that geometric phase modulation is employed, and 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 forming photo-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 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:

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.