A topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal and its preparation method

Abstract

A topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal and a preparation method thereof belong to the technical field of adjustable terahertz vortex beams. In order to solve the problem of extensive and precise adjustment of the generated vortex beam, the present invention is provided with a first substrate layer, a rotationally twisted electrode layer, a first polyimide orientation layer, an electrically controlled liquid crystal layer, a second polyimide orientation layer, a uniform transparent electrode layer, and a second substrate layer in sequence from top to bottom; the rotationally twisted electrode layer is composed of a series of discrete petal electrodes, and each petal electrode is connected to a multi-channel control power supply via an electrode connecting line; a series of discrete petal electrodes are formed by a series of concentric fan-shaped rotational twists, and are used to generate an electric field distribution to excite the electrically controlled liquid crystal layer to generate a vortex beam phase. The present invention realizes the generation of a vortex beam and can adjust the topological charge using a relatively simple structure, with obvious effects and can simplify the relevant optical system.

Description

Technical Field

[0001] The present invention belongs to the technical field of adjustable terahertz vortex beams, and particularly relates to a topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal and a preparation method thereof. Background Art

[0002] Terahertz waves, with a frequency between microwaves and infrared (0.1-10 THz), have broad application potential in fields such as security testing, communications, materials analysis, and medical imaging, making them a key area of ​​scientific research and technological development. Liquid crystal patterning control technology is a passive control method for engineering the terahertz wavefront, enabling single or multiple control of properties such as the amplitude and phase of the terahertz light field. In recent years, with the continuous expansion of terahertz beam systems, the demand for high-quality, integrated, and diversified structured beam generation devices has increased, promoting the development and updating of customized engineering solutions and the design of adjustable structured beam devices.

[0003] Terahertz vortex beams are a unique beam form in the terahertz band that combines the characteristics of terahertz technology and vortex beams. By introducing a specific spiral phase structure, this type of beam forms a complex light field distribution carrying orbital angular momentum (OAM), allowing the beam to carry multiple discrete OAM states, providing a new dimension for information encoding, transmission, and processing. Terahertz vortex beams not only inherit the advantages of terahertz waves such as strong penetration and sensitivity to material properties, but also have higher information carrying capacity and control accuracy due to their unique OAM characteristics. This feature makes terahertz vortex beams show great potential in high-speed, large-capacity communication systems, especially in data transmission scenarios that require high security and high efficiency, such as near-field communication and next-generation wireless network communication (6G).

[0004] Currently, the main methods for generating terahertz vortex beams include traditional polymer lenses and splicing half-wave plates with different optical axis orientations. These solutions suffer from large device sizes, difficult processing, and low efficiency. Newer solutions include metasurfaces based on transmission phase or geometric phase, and liquid crystal wave plates using geometric phase optical orientation. The former utilizes metal or dielectric metasurfaces to introduce multi-order phase modulation factors, enabling the generation of vortex beams when incident with linearly or circularly polarized terahertz plane waves. The latter utilizes liquid crystal optical orientation technology to control the arrangement of liquid crystal pointing angles, enabling the fabrication of spiral phase plates in the terahertz band. While these solutions improve device thinness and lightweight, they suffer from drawbacks such as poor versatility and the inability to adjust the generated beam. With the continuous development of terahertz beam systems, there is an urgent need for device solutions that are simple to process, highly integrated, lightweight, and capable of extensive and precise adjustment of the generated vortex beam. Summary of the Invention

[0005] The problem to be solved by the present invention is to achieve simple and convenient processing, high integration, lightness and thinness, and the ability to perform extensive and precise adjustment of the generated vortex beam. A topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal and its preparation method are proposed.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystals comprises, from top to bottom, a first substrate layer, a rotationally twisted electrode layer, a first polyimide alignment layer, an electrically controlled liquid crystal layer, a second polyimide alignment layer, a uniform transparent electrode layer, and a second substrate layer;

[0008] The rotationally twisted electrode layer is composed of a series of discrete petal-shaped electrodes, each of which is connected to a multi-channel control power supply via an electrode connecting line; the series of discrete petal-shaped electrodes are formed by a series of concentric fan-shaped rotational twists, and are used to generate an electric field distribution to excite the electrically controlled liquid crystal layer to generate a vortex beam phase.

[0009] Furthermore, the expression of the phase distribution provided by the rotationally twisted electrode layer is:

[0010]

[0011] in, is the phase distribution provided by the rotationally twisted electrode layer, H is the Heaviside step function, λ is the terahertz wavelength, f is the focal length parameter used to provide focusing to converge the vortex light, r is the radial coordinate of the point on the electrode layer, l is the topological charge of the vortex light, and i is the imaginary unit.

[0012] Furthermore, the first substrate layer and the second substrate layer are terahertz transparent quartz or silicon substrates; the number of petal electrodes in the rotationally twisted electrode layer is 12-48, and each petal electrode can be divided into two states, 1 and 0, based on power supply and no power supply.

[0013] Furthermore, the electrically controlled liquid crystal layer is used to cooperate with the rotationally twisted electrode layer to provide a phase delay of the sampled vortex beam. The first polyimide alignment layer and the second polyimide alignment layer are antiparallel aligned to constrain the liquid crystal alignment near the upper and lower boundaries. The electrically controlled liquid crystal layer generates a single-valued phase delay δ corresponding to the voltage through the birefringence effect of the liquid crystal, which is expressed as:

[0014]

[0015] Where d is the thickness of the electrically controlled liquid crystal layer, θ is the change in the liquid crystal deflection angle with thickness, and n ⊥ and n ||are the refractive index when the polarization direction of the incident light is perpendicular to the pointing angle of the liquid crystal molecules and the refractive index when the polarization direction of the incident light is parallel to the pointing angle of the liquid crystal molecules, respectively; z is the thickness direction coordinate of the point in the electrically controlled liquid crystal layer;

[0016] The thickness of the electrically controlled liquid crystal layer depends on the birefringence of the liquid crystal, ensuring that the liquid crystal provides a phase shift of an angle of π after full deflection.

[0017] Furthermore, the uniform transparent electrode layer is grounded when powered, so as to provide a reference potential for the rotationally twisted electrode layer.

[0018] A method for preparing a terahertz vortex beam generating device with adjustable topological charge based on electrically controlled liquid crystal is implemented based on the aforementioned terahertz vortex beam generating device with adjustable topological charge based on electrically controlled liquid crystal, and comprises the following steps:

[0019] S1. Depositing a 30 nm to 100 nm thick dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer on the second substrate using a thin film deposition process to obtain a uniform transparent electrode layer;

[0020] S2. Depositing a 30 nm to 100 nm thick dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer on the first substrate using a thin film deposition process, and then patterning the layer using a standard photolithography process to obtain a rotationally twisted electrode layer;

[0021] S3. Spin-coating a second polyimide alignment layer and a first polyimide alignment layer on the uniform transparent electrode layer and the rotationally twisted electrode layer, respectively. The layers are then baked at a high temperature and then rubbed along the x-axis to ensure that the rubbing directions of the first and second polyimide alignment layers are antiparallel.

[0022] S4. Calculate the thickness of the electrically controlled liquid crystal layer based on the birefringence of the liquid crystal, assemble the liquid crystal box, fill the liquid crystal between the first polyimide orientation layer and the second polyimide orientation layer, and then seal the layer with glue to obtain a topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal.

[0023] Furthermore, the thin film deposition process in step S1 and step S2 is a spin coating process, wherein 5 Vol% to 15 Vol% DMSO is mixed into the PEDOT:PSS solution, followed by stirring for 1 to 1.5 hours, and then the stirred solution is filtered through a 0.45 μm syringe filter to obtain a uniformly mixed PEDOT:PSS doped solution to spin-coat a dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer, the spin coating speed is 2000 rpm to 8000 rpm, and the spin coating time is 30 s to 90 s.

[0024] Furthermore, the patterning method in step S2 is to adopt a standard photolithography process and a lift-off stripping method to obtain a rotationally twisted electrode layer, and the specific implementation method is as follows:

[0025] First, the surface of the first substrate layer was rinsed with deionized water, then ultrasonically cleaned with deionized water, ethanol, and isopropanol for 10 minutes each to remove dust and oil on the surface, and then dried with dry high-purity nitrogen gas;

[0026] Spin the cleaned first base layer with a photoresist at a speed of 2000 rpm to 6000 rpm for about 60 seconds.

[0027] After the photoresist is spin-coated, it is placed on a hot plate for pre-baking at 100°C for 90 seconds.

[0028] Then, a photolithography machine is used to expose and write the pattern designed on the mask to the photoresist to transfer the pattern;

[0029] After exposure, the sample was post-baked on a 105°C hot plate for 90 seconds. After post-baking, the treated sample was placed in a developer and developed for about 30 seconds to obtain a patterned photoresist layer.

[0030] Then, the first substrate layer with the transparent electrode spin-coated was transferred to a hot plate and baked at 90°C for 5 minutes to evaporate the water and form a complete film;

[0031] The photoresist is then stripped off, ultrasonically shaken in NMP for 20 seconds, and then blown dry with high-purity nitrogen to obtain a rotationally twisted electrode layer.

[0032] Furthermore, in step S3, commercial polyimide is spin-coated at a spin-coating speed of 2000 rpm to 4000 rpm for 30 s to 90 s, and after spin-coating, the substrate is baked at a high temperature of 200-240° C. for 2-2.5 hours.

[0033] Furthermore, in step S4, based on the birefringence being 0.28, the thickness of the electrically controlled liquid crystal layer being 400 μm, and the maximum birefringence phase shift of the liquid crystal being π at a driving voltage of 5 V, a liquid crystal cell is assembled, and the thickness of the liquid crystal layer is controlled to be 400 μm.

[0034] Beneficial effects of the present invention:

[0035] The present invention describes a topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal, which is dedicated to meeting the urgent needs of terahertz structure beam modulation devices for miniaturization and integration. By utilizing patterned liquid crystal driving technology, a topological charge adjustable terahertz vortex beam generating device and its design method are proposed. A transparent patterned electrode layer suitable for the terahertz frequency band is manufactured using patterned etching technology. When powered on, the layer can form a specific rotationally twisted fan-shaped voltage distribution. Furthermore, through carefully designed structural layout and thickness selection, a rotationally twisted fan-shaped phase pattern can be constructed in the liquid crystal layer. By adjusting the power supply voltage sequence, the device can generate vortex beams with different topological charges. The advantages of this solution are simple device structure, low cost, high integration and good compatibility with semiconductor processes. Only a relatively simple single-channel external circuit is required to achieve relatively accurate regulation of the topological charge of the vortex beam.

[0036] The present invention describes a terahertz vortex beam generating device with adjustable topological charge based on electrically controlled liquid crystals. This device is designed to meet the needs of miniaturization and integration of terahertz structure beam modulation devices. It can be realized by simply combining a sandwich liquid crystal box structure with patterned electrodes, resulting in low cost, high integration, simple device manufacturing and processing technology, and compatibility with semiconductor processes. A terahertz patterned transparent electrode layer is prepared using a patterned etching process, and a specific light field distribution is achieved after power is applied, enabling customized design of a control device for a given light field. The topological charge of the generated vortex beam is adjustable, achieving the generation of a vortex beam and the ability to adjust the topological charge using a relatively simple structure. This has a significant effect and can simplify related optical systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic structural diagram of a topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal according to the present invention;

[0038] Figure 2 A diagram showing the connection relationship of the rotationally twisted electrode layer according to the present invention;

[0039] Figure 3 This is the beam result diagram of the / 1{12}0{12} / electrode sequence of the present invention;

[0040] Figure 4 This is the beam result diagram of the / 1{6}0{6}… / electrode sequence of the present invention. DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention and are not intended to limit the present invention. That is, the specific embodiments described herein are only some embodiments of the present invention, not all embodiments. Generally, the components of the specific embodiments of the present invention described and illustrated in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0042] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected specific embodiments of the present invention. All other specific embodiments obtained by those skilled in the art based on the specific embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] In order to further understand the content, features and effects of the present invention, the following specific embodiments are given as examples, and the attached Figure 1 -Attached Figure 4 The detailed instructions are as follows:

[0044] Example 1:

[0045] A topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystals, which comprises, from top to bottom, a first substrate layer 1, a rotationally twisted electrode layer 2, a first polyimide alignment layer 3, an electrically controlled liquid crystal layer 4, a second polyimide alignment layer 5, a uniform transparent electrode layer 6, and a second substrate layer 7;

[0046] The rotationally twisted electrode layer 2 is composed of a series of discrete petal-shaped electrodes 10, each petal-shaped electrode is connected to a multi-channel control power supply 9 via an electrode connecting line 8; the series of discrete petal-shaped electrodes 10 are formed by a series of concentric fan-shaped rotational twists, and are used to generate an electric field distribution to excite the electrically controlled liquid crystal layer 4 to generate a vortex beam phase.

[0047] Furthermore, the expression of the phase distribution provided by the rotationally twisted electrode layer 2 is:

[0048]

[0049] in, is the phase distribution provided by the rotationally twisted electrode layer 2, H is the Heaviside step function, λ is the terahertz wavelength, f is the focal length parameter used to provide focusing to converge the vortex light, r is the radial coordinate of the point on the electrode layer, l is the topological charge number of the vortex light, and i is the imaginary unit.

[0050] Furthermore, the first substrate layer 1 and the second substrate layer 7 are terahertz transparent quartz or silicon substrates; the number of petal electrodes 10 in the rotationally twisted electrode layer 2 is 12-48, and each petal electrode 10 can be divided into two states, 1 and 0, based on power supply and no power supply.

[0051] Furthermore, the degree of rotational distortion is determined by the design focal length of the device. The larger the focal length, the smaller the degree of rotational distortion. Each of the discrete petal electrodes in the rotationally twisted electrode layer can be independently powered, and the voltage can be independently adjusted. Each electrode can be divided into two states, "1" and "0", depending on whether it is powered or not. Furthermore, the discrete petal electrodes have two rotation directions, depending on the positive or negative topological charge to be generated. Here, the electrode has a clockwise rotation direction along the light-transmitting direction, which can generate a vortex beam with a positive topological charge. The number of petal electrodes in the designed device should not be too few or too many, and the effect should be better between 12 and 48. Too few will result in the inability to provide effective phase sampling, and too many will result in a reduction in the contrast of the liquid crystal phase.

[0052] Furthermore, the electrically controlled liquid crystal layer 4 is used to cooperate with the rotationally twisted electrode layer 2 to provide a phase delay of the sampled vortex beam. The first polyimide alignment layer 3 and the second polyimide alignment layer 5 are antiparallel aligned to constrain the liquid crystal alignment near the upper and lower boundaries. The electrically controlled liquid crystal layer 4 generates a single-valued phase delay δ corresponding to the voltage through the birefringence effect of the liquid crystal, which is expressed as:

[0053]

[0054] Where d is the thickness of the electrically controlled liquid crystal layer, θ is the change in the liquid crystal deflection angle with thickness, and n ⊥ and n || are the refractive index when the polarization direction of the incident light is perpendicular to the pointing angle of the liquid crystal molecules and the refractive index when the polarization direction of the incident light is parallel to the pointing angle of the liquid crystal molecules, respectively; z is the thickness direction coordinate of the point in the electrically controlled liquid crystal layer 4;

[0055] The thickness of the electrically controlled liquid crystal layer 4 depends on the birefringence of the liquid crystal, ensuring that the liquid crystal provides a phase shift of an angle of π after full deflection.

[0056] Furthermore, the birefringence of the liquid crystal used, Δn = 0.28, the thickness of the liquid crystal layer, and the wavelength of the terahertz wave, 118 μm, ensure a maximum phase shift exceeding π. Combined with the power supply state of each electrode, the liquid crystal deflection phase shift in the "1" state must be precisely controlled to π. The power supply voltage used in this "1" state is 4.7V. The discrete petal-shaped electrodes, in conjunction with the liquid crystal, produce a phase distribution consistent with its shape, forming a vortex half-wave plate for the terahertz band.

[0057] Furthermore, the uniform transparent electrode layer 6 is grounded when powered, so as to provide a reference potential for the rotationally twisted electrode layer 2 .

[0058] Furthermore, the rotationally twisted electrode layer and the uniform transparent electrode layer require an amplitude transmittance of more than 70%, otherwise the quality of the output light beam may be poor.

[0059] The principle of this embodiment utilizes the electrically controlled phase modulation function of nematic liquid crystals, combined with terahertz transparent electrodes, to achieve customized phase modulation on the device. By generating a vortex beam phase distribution within the device, incident light is converted into a vortex beam. By binarizing and restoring the different vortex beam phase distributions and combining them with the angular periodicity of the vortex light phase, the generation and conversion of multiple topologically charged vortex beams can be integrated into a single device.

[0060] The driving and vortex light switching effect of this embodiment is as follows: Figure 2 As shown, each electrode 1 is independently led out to a control power supply 3 through an electrode connection line 2 for independent voltage control. Figure 1 The uniform transparent electrode layer 6 in the embodiment is grounded (0V) when powered and serves as a reference potential. The electrode array is driven by digital coding, and each electrode can be divided into two states, "1" and "0", depending on whether it is powered or not. The "1" state corresponds to a phase delay of π for the liquid crystal under the electrode, and the "0" state corresponds to a phase delay of 0 for the liquid crystal under the electrode. The phase delays corresponding to power on and power off differ by π. By changing the voltage sequence, the topological charge of the vortex light generated in this embodiment can be controlled. Due to the limitations of the liquid crystal thickness and the periodicity of the vortex phase angle, a 24-electrode number can generate vortex light with topological charges of 1, 2, 3, 4, and 6, and the electrode sequences corresponding to each topological charge are: / 1{12}0{12} / , / 1{6}0{6}… / , / 11110000… / , / 111000… / , / 1100… / . 1{12} represents 12 consecutive occurrences of 1, and the same applies to the other representations.

[0061] Figure 3 and Figure 4 The results are for beams with electrode sequences of / 1{12}0{12} / and / 1{6}0{6}… / , respectively, with topological charges of 1 and 2, respectively. By changing the switching sequence of the discrete electrodes, the phase distribution generated by the liquid crystal can be adjusted to align with the petal-shaped electrodes, thereby varying the topological charge generated by the device.

[0062] The terahertz transparent electrode layer described in this embodiment can be replaced with other thin films capable of achieving high terahertz transmittance and high conductivity, such as graphene, carbon nanotubes, and transparent conductive metal films. The number of fan-shaped structures in the patterned transparent electrode layer described in this embodiment is not limited to this embodiment; for example, a higher number can be used, provided that the corresponding circuit is used.

[0063] Example 2:

[0064] A method for preparing a terahertz vortex beam generating device with adjustable topological charge based on electrically controlled liquid crystal is implemented based on the terahertz vortex beam generating device with adjustable topological charge based on electrically controlled liquid crystal described in Example 1, and includes the following steps:

[0065] S1. Depositing a 30 nm to 100 nm thick dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer on the second substrate using a thin film deposition process to obtain a uniform transparent electrode layer;

[0066] Furthermore, the thin film deposition process in step S1 and step S2 is a spin coating process, wherein 5 Vol% to 15 Vol% DMSO is mixed into the PEDOT:PSS solution, followed by stirring for 1 to 1.5 hours, and then the stirred solution is filtered through a 0.45 μm syringe filter to obtain a uniformly mixed PEDOT:PSS doped solution for spin coating a dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer, the spin coating speed is 2000 rpm to 8000 rpm, and the spin coating time is 30 s to 90 s;

[0067] S2. Depositing a 30 nm to 100 nm thick dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer on the first substrate using a thin film deposition process, and then patterning the layer using a standard photolithography process to obtain a rotationally twisted electrode layer;

[0068] Furthermore, the patterning method in step S2 is to adopt a standard photolithography process and a lift-off stripping method to obtain a rotationally twisted electrode layer, and the specific implementation method is as follows:

[0069] First, the surface of the first substrate layer was rinsed with deionized water, then ultrasonically cleaned with deionized water, ethanol, and isopropanol for 10 minutes each to remove dust and oil on the surface, and then dried with dry high-purity nitrogen gas;

[0070] Spin the cleaned first base layer with a photoresist at a speed of 2000 rpm to 6000 rpm for about 60 seconds.

[0071] After the photoresist is spin-coated, it is placed on a hot plate for pre-baking at 100°C for 90 seconds.

[0072] Then, a photolithography machine is used to expose and write the pattern designed on the mask to the photoresist to transfer the pattern;

[0073] After exposure, the sample was post-baked on a 105°C hot plate for 90 seconds. After post-baking, the treated sample was placed in a developer and developed for about 30 seconds to obtain a patterned photoresist layer.

[0074] Then, the first substrate layer with the transparent electrode spin-coated was transferred to a hot plate and baked at 90°C for 5 minutes to evaporate the water and form a complete film;

[0075] The photoresist is then stripped off, ultrasonically shaken in NMP for 20 seconds, and then blown dry with high-purity nitrogen to obtain a rotationally twisted electrode layer.

[0076] S3. Spin-coating a second polyimide alignment layer and a first polyimide alignment layer on the uniform transparent electrode layer and the rotationally twisted electrode layer, respectively. The layers are then baked at a high temperature and then rubbed along the x-axis to ensure that the rubbing directions of the first and second polyimide alignment layers are antiparallel.

[0077] Furthermore, in step S3, commercial polyimide is spin-coated at a spin-coating speed of 2000 rpm to 4000 rpm for 30 s to 90 s, and after spin-coating, the substrate is baked at a high temperature of 200-240° C. for 2-2.5 hours.

[0078] S4. Calculate the thickness of the electrically controlled liquid crystal layer based on the birefringence of the liquid crystal, assemble the liquid crystal box, fill the liquid crystal between the first polyimide orientation layer and the second polyimide orientation layer, and then seal the layer with glue to obtain a topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal.

[0079] Furthermore, in step S4, based on the birefringence being 0.28, the thickness of the electrically controlled liquid crystal layer being 400 μm, and the maximum birefringence phase shift of the liquid crystal being π at a driving voltage of 5 V, a liquid crystal cell is assembled, and the thickness of the liquid crystal layer is controlled to be 400 μm.

[0080] Furthermore, the large birefringence nematic liquid crystal is sealed after filling. In practical applications, other nematic liquid crystals can also be used, and the thickness and driving voltage of the corresponding electrically controlled liquid crystal layer 4 need to be adjusted to meet the birefringence phase shift of the corresponding liquid crystal layer.

[0081] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0082] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, as long as there are no structural conflicts, the various features of the embodiments disclosed herein may be combined with each other in any manner, and the omission of an exhaustive description of these combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions within the scope of the claims.

Claims

1. A topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal, characterized in that: From top to bottom, a first substrate layer (1), a rotationally twisted electrode layer (2), a first polyimide alignment layer (3), an electrically controlled liquid crystal layer (4), a second polyimide alignment layer (5), a uniform transparent electrode layer (6), and a second substrate layer (7) are sequentially provided; The rotationally twisted electrode layer (2) is composed of a series of discrete petal-shaped electrodes (10), each petal-shaped electrode being connected to a multi-channel control power supply (9) via an electrode connection line (8); the series of discrete petal-shaped electrodes (10) are formed by a series of concentric fan-shaped rotational twists, and are used to generate an electric field distribution to excite the electrically controlled liquid crystal layer (4) to generate a vortex beam phase; The expression of the phase distribution provided by the rotationally twisted electrode layer (2) is: in, is the phase distribution provided by the rotationally twisted electrode layer (2), H is the Heaviside step function, λ is the terahertz wavelength, f is the focal length parameter used to provide focusing to converge the vortex light, r is the radial coordinate of a point on the electrode layer, l is the topological charge number of the vortex light, and i is an imaginary unit; The first substrate layer (1) and the second substrate layer (7) are terahertz-transparent quartz or silicon substrates; the number of petal-shaped electrodes (10) in the rotationally twisted electrode layer (2) is 12-48, and each petal-shaped electrode (10) can be divided into two states, 1 and 0, based on power supply and no power supply; The electrically controlled liquid crystal layer (4) is used to cooperate with the rotationally twisted electrode layer (2) to provide a phase delay of the sampled vortex light beam. The first polyimide orientation layer (3) and the second polyimide orientation layer (5) are antiparallel oriented to constrain the liquid crystal orientation near the upper and lower boundaries. The electrically controlled liquid crystal layer (4) generates a single-value phase delay δ corresponding to the voltage through the birefringence effect of the liquid crystal, and the expression is: Where d is the thickness of the electrically controlled liquid crystal layer, θ is the change in the liquid crystal deflection angle with thickness, and n ⊥ and n || are the refractive index when the polarization direction of the incident light is perpendicular to the pointing angle of the liquid crystal molecules and the refractive index when the polarization direction of the incident light is parallel to the pointing angle of the liquid crystal molecules, respectively; z is the thickness direction coordinate of a point in the electrically controlled liquid crystal layer (4); The thickness of the electrically controlled liquid crystal layer (4) depends on the birefringence of the liquid crystal, ensuring that the liquid crystal provides a phase shift of an angle of π after full deflection.

2. The topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal according to claim 1, characterized in that: The uniform transparent electrode layer (6) is grounded when powered, and is used to provide a reference potential for the rotationally twisted electrode layer (2).

3. A topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal according to claim 1 or 2, characterized in that: The method for preparing a topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal comprises the following steps: S1. Depositing a 30 nm to 100 nm thick dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer on the second substrate using a thin film deposition process to obtain a uniform transparent electrode layer; S2. Depositing a 30 nm to 100 nm thick dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer on the first substrate using a thin film deposition process, and then patterning the layer using a standard photolithography process to obtain a rotationally twisted electrode layer; S3. Spin-coating a second polyimide alignment layer and a first polyimide alignment layer on the uniform transparent electrode layer and the rotationally twisted electrode layer, respectively. The layers are then baked at a high temperature and then rubbed along the x-axis to ensure that the rubbing directions of the first and second polyimide alignment layers are antiparallel. S4. Calculate the thickness of the electrically controlled liquid crystal layer based on the birefringence of the liquid crystal, assemble the liquid crystal box, fill the liquid crystal between the first polyimide orientation layer and the second polyimide orientation layer, and then seal the layer with glue to obtain a topological charge-adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal.

4. The topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal according to claim 3, characterized in that: The thin film deposition process in step S1 and step S2 is a spin coating process, wherein 5 Vol% to 15 Vol% DMSO is mixed into the PEDOT:PSS solution, followed by stirring for 1 to 1.5 hours. Then, the stirred solution is filtered through a 0.45 μm syringe filter to obtain a uniformly mixed PEDOT:PSS doped solution for spin coating a dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) terahertz transparent electrode layer. The spin coating speed is 2000 rpm to 8000 rpm, and the spin coating time is 30 s to 90 s.

5. The topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal according to claim 4, characterized in that: The method for patterning in step S2 is to adopt a standard photolithography process and use a lift-off stripping method to obtain a rotationally twisted electrode layer. The specific implementation method is as follows: First, the surface of the first substrate layer was rinsed with deionized water, then ultrasonically cleaned with deionized water, ethanol, and isopropanol for 10 minutes each to remove dust and oil on the surface, and then dried with dry high-purity nitrogen gas; Spin the cleaned first base layer with a photoresist at a speed of 2000 rpm to 6000 rpm for about 60 seconds. After the photoresist is spin-coated, it is placed on a hot plate for pre-baking at 100°C for 90 seconds. Then, a photolithography machine is used to expose and write the pattern designed on the mask to the photoresist to transfer the pattern; After exposure, the sample was post-baked on a 105°C hot plate for 90 seconds. After post-baking, the treated sample was placed in a developer and developed for about 30 seconds to obtain a patterned photoresist layer. Then, the first substrate layer with the transparent electrode spin-coated was transferred to a hot plate and baked at 90°C for 5 minutes to evaporate the water and form a complete film; The photoresist is then stripped off, ultrasonically shaken in NMP for 20 seconds, and then blown dry with high-purity nitrogen to obtain a rotationally twisted electrode layer.

6. The topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal according to claim 5, characterized in that: In step S3 , commercial polyimide is spin-coated at a spin-coating speed of 2000 rpm to 4000 rpm for 30 s to 90 s. After spin-coating, the substrate is baked at a high temperature of 200-240° C. for 2-2.5 hours.

7. The topological charge adjustable terahertz vortex beam generating device based on electrically controlled liquid crystal according to claim 6, characterized in that: In step S4, based on the birefringence being 0.28, the thickness of the electrically controlled liquid crystal layer being 400 μm, and the maximum birefringence phase shift of the liquid crystal being π at a driving voltage of 5 V, a liquid crystal cell is assembled and the thickness of the liquid crystal layer is controlled to be 400 μm.

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