Dynamic phase reconstruction technology of patterned terahertz liquid crystal transparent electrode

Abstract

The invention discloses a dynamic phase reconstruction technology of a patterned terahertz (THz) liquid crystal transparent electrode, and belongs to the technical field of terahertz application. The specific implementation method is as follows: the PVA-graphene conductive THz transparent film is prepared by utilizing the strong adhesive force of polyvinyl alcohol (PVA) and combining the high transmittance, high carrier mobility and excellent chemical stability of graphene at the THz wave band. And then, processing the thin film by adopting an ultraviolet laser etching technology to manufacture a micro-structure patterned electrode. Furthermore, the patterned graphene transparent film positive electrode layer, the liquid crystal layer and the graphene transparent film negative electrode layer are combined, and sub-wavelength pixelated liquid crystal spatial light phase regulation is achieved. According to the technology, the THz light field phase distribution of the liquid crystal can be spatially coded by patterning the terahertz liquid crystal transparent electrode array, and the regulation of a single pixel element is expanded from a simple on-off state to multi-level state regulation under different voltages. According to the invention, a technical foundation is laid for research and development of a high-performance terahertz spatial light modulator, and development of the fields of terahertz spatial light information processing, holographic technology and the like is expected to be promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz applications, and particularly relates to a dynamic phase reconstruction technology based on a patterned terahertz liquid crystal transparent electrode. Background Art

[0002] Terahertz (THz) waves are located at the intersection of electronics and photonics. This unique electromagnetic spectrum position endows it with many significant advantages and is a key wavelength band for realizing new-generation information technologies such as 6G wireless communication, high-precision radar detection, and intelligent sensing. However, with the rapid development of THz science and technology, the current ability to precisely control key optical field information such as amplitude, phase, and polarization is significantly insufficient, and existing THz spatial light phase modulation devices all face bottlenecks such as narrow working frequencies, low modulation efficiency, and low degrees of freedom in modulation, making it difficult to meet the growing demands of information systems for communication capacity and intelligent control. Against this background, it is particularly urgent to develop new THz spatial light phase spatio-temporal dynamic modulation devices that can efficiently and flexibly control electromagnetic parameters.

[0003] Liquid crystals, with their significant dielectric anisotropy and external field modulation characteristics in the ultra-wide electromagnetic frequency band, exhibit advantages in spatial light phase modulation that cannot be compared with other functional materials. In recent years, many progress has been made in the field of THz liquid crystal spatial light phase modulation. However, existing devices have limitations in dynamic modulation capabilities and degrees of freedom in modulation. Traditional external field application methods, such as the very low transmittance of ITO electrodes in the THz band [Coatings, 2024, 14, 895], and patterned metal structure electrodes, due to simultaneously acting as both THz artificial resonance or phase shift functional units and liquid crystal driving electrodes [Nat. Commun. 2025, 16, 1836], result in reduced device efficiency, limited design flexibility, and high insertion losses. Graphene has excellent THz transmittance [Light Sci. Appl. 2022, 11, 191], high carrier mobility [Laser Photonics Rev 2024, n / a, 2301301], and excellent chemical stability [Chem. Eng. J. 2025, 508, 160721], and can be used to fabricate tunable transparent electrodes. However, most current graphene electrodes operate with a uniform bias voltage applied to the entire thin film and have not achieved pixelated liquid crystal spatial light phase modulation. Summary of the Invention

[0004] In order to break through the limitations of current THz liquid crystal devices in modulation principles and technologies, and to solve the problems of poor dynamic modulation ability and low modulation freedom of existing devices, the present invention provides a dynamic phase reconstruction technology based on a patterned terahertz liquid crystal transparent electrode. By combining a patterned graphene transparent thin film positive electrode layer, a liquid crystal layer, and a graphene transparent thin film negative electrode layer, sub-wavelength pixelated liquid crystal spatial light phase modulation is achieved.

[0005] The technical solution of the present invention is as follows: The device structure of the patterned THz liquid crystal transparent electrode of the present invention mainly consists of three parts: a patterned graphene transparent thin film positive electrode layer, a liquid crystal layer, and a graphene transparent thin film negative electrode layer. Among them, the graphene transparent thin film electrode layer is a conductive THz transparent thin film prepared by mixing polyvinyl alcohol and graphene in a certain proportion. Preferably, the porous graphene structure can maximize the high transmittance of THz waves; polyvinyl alcohol and graphene are mixed in a ratio of about 2:1 to maximize the mechanical strength and chemical stability of the THz transparent thin film; after the mixed solution is evenly coated on a glass substrate, it should be dried in a dryer for ≥ 2 h to control the degree of graphene oxidation-reduction to maximize the high conductivity of the THz transparent thin film. The patterned graphene transparent thin film positive electrode layer is prepared by using ultraviolet laser etching technology to evenly divide the thin film into multiple pixel units. Preferably, the number of spatial pixel units should be ≥ 8. Due to the phase delay condition , the thickness d of the liquid crystal layer is inversely proportional to the birefringence coefficient Δn . Preferably, a liquid crystal material with a birefringence coefficient ≥ 0.25 should be selected.

[0006] The working principle of the present invention is: Under the combined action of an alignment layer in which liquid crystal molecules are arranged in an arbitrary direction in the xoy plane and an external electric field along the light propagation direction (z-axis direction), the liquid crystal molecules can rotate arbitrarily in space, which plays a decisive role in the device performance. By applying different electric fields to different pixel units of the THz liquid crystal transparent electrode, angle space encoding is achieved. Among them, the encoding method in which no voltage is applied and the liquid crystal main axis is oriented in the xoy plane is called encoding 0, and the corresponding phase value > 0. The encoding method with a voltage of 30 V to 50 V applied is called encoding 1, and the corresponding phase value is 0. Further, for a single pixel unit, as the external voltage increases non-linearly, the liquid crystal exhibits multiple different spatial states, thereby realizing dynamic phase reconstruction with multi-pixel and multi-level encoding control.

[0007] The working method of the present invention is as follows: Connect the patterned THz liquid crystal transparent electrode to the PCB circuit board, and perform spatio-temporal programming on the device using a programmable power supply or FPGA. Use a near-field / far-field scannable THz time-domain spectroscopy system to collect xoy the time-domain signal of the surface, and perform Fourier transform on this signal to map the time-domain information into frequency-domain information in order to obtain the intensity and phase distribution maps.

[0008] The beneficial effects and advantages of the present invention are as follows: The present invention uses a PVA-graphene conductive film to prepare a THz liquid crystal transparent electrode, which not only reduces the manufacturing cost, but also has high transmittance and conductivity, excellent mechanical strength and chemical stability.

[0009] The present invention uses ultraviolet laser etching of the graphene conductive film, and the preparation process is simple and time-consuming is short, providing a new idea for solving the problems of THz transparent electrode materials and processing technologies.

[0010] The present invention uses a terahertz transparent electrode with a patterned graphene layer to solve the driving problem of non-metallic metasurface liquid crystal integrated devices, breaking through the limitations of the principles and technologies of existing traditional metal or ITO patterned electrodes for regulating THz liquid crystal devices, and realizing high-transparency independent electrode liquid crystal control.

[0011] The present invention performs spatio-temporal coding control through a programmable power supply or FPGA, realizing dynamic phase reconstruction of multi-pixel and multi-level coding control, laying a foundation for the development of high-performance THz spatial light modulators, and is expected to promote the development of fields such as terahertz spatial light information processing and holography technology. Description of the Drawings

[0012] Figure 1 (a) is a structural diagram of a patterned THz liquid crystal transparent electrode device provided by an embodiment of the present application; Figure 1 (b) is a patterned THz transparent electrode after welding electrode leads on a PCB circuit board in an embodiment of the present application; Figure 2 (a) is a physical diagram of a patterned THz liquid crystal transparent electrode device in an embodiment of the present application; Figure 2 (b) is a microscopic image of a patterned THz liquid crystal transparent electrode device in an embodiment of the present application Figure 3 (a) is a distribution map of the sheet resistance of a THz transparent thin film in an embodiment of the present application; Figure 3(b) is the thickness profile of the THz transparent thin film in the embodiment of the present application; Figure 4 is the near-field / far-field scannable terahertz time-domain spectroscopy system in the experiment verification of the embodiment of the present application; Figure 5 is the transmittance of the patterned THz liquid crystal transparent electrode measured in the experiment of the embodiment of the present application; Figure 6 (a) is the experimental phase distribution when the angular space encoding is 11110000... in the embodiment of the present application; Figure 6 (b) is the experimental phase distribution when the angular space encoding is 11001100... in the embodiment of the present application; Figure 6 (c) is the experimental phase distribution when the angular space encoding is 10101010... in the embodiment of the present application; Figure 7 (a) is the experimental intensity distribution when the angular space encoding is 11110000... in the embodiment of the present application; Figure 7 (b) is the experimental intensity distribution when the angular space encoding is 11001100... in the embodiment of the present application; Figure 7 (c) is the experimental intensity distribution when the angular space encoding is 10101010... in the embodiment of the present application; Figure 8 (a) is the time-domain signal under the control of 5 different voltages at any spatial pixel point in the embodiment of the present application; Figure 8 (b) is the phase difference at 0.55 THz frequency under 5-level encoding at any spatial pixel point in the embodiment of the present application. Detailed implementation manners

[0013] Combined with the accompanying drawings of the specification, the present invention elaborates in detail on the dynamic phase reconstruction technology based on the patterned terahertz liquid crystal transparent electrode. It should be noted that the present invention can be implemented in many other ways different from this description, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0014] In the description of the present invention, it should be clear that the terms "upper", "lower", " x direction", " y direction", " z direction", " xoyThe orientation or positional relationship indicated by terms such as "plane" and "near field" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0015] The present invention discloses a dynamic phase reconstruction technology for patterned terahertz liquid crystal transparent electrodes, and its embodiments are as follows: This embodiment demonstrates a patterned THz liquid crystal transparent electrode device. As Figure 1 shown in (a), the device structure mainly includes three parts: a patterned graphene transparent thin film positive electrode layer, a liquid crystal layer, and a graphene transparent thin film negative electrode layer. As Figure 1 shown in (b), when the device is regulated, metal leads need to be welded on the patterned graphene transparent thin film positive electrode layer and the graphene transparent thin film negative electrode layer, and the leads are connected to a PCB circuit board, and then the spatio-temporal programming of the device is realized through an FPGA. The design process of the device will be briefly introduced below. First, polyvinyl alcohol particles and deionized water are mixed according to a mass ratio of 1:10, and a polyvinyl alcohol solution is prepared by means of water bath heating and magnetic stirring. Then, 1 mL of the polyvinyl alcohol solution and 2 mL of the graphene dispersion are respectively measured with a pipette and placed in a test tube. After 5 minutes of mechanical oscillation and 10 minutes of ultrasonic oscillation, a uniform polyvinyl alcohol-graphene mixed solution can be obtained. Subsequently, the mixed solution is uniformly coated on a non-doped fused silica optical glass substrate with a thickness of 500 μm and a size of 30 mm×30 mm. After it is naturally air-dried at room temperature for about 20 minutes, it is then placed in a dryer and dried at a temperature of 180°C for 2.5 hours, and finally a THz transparent thin film with conductive performance is prepared.

[0016] As Figure 2 shown, using a four-probe tester and a three-dimensional surface profiler, the sheet resistance and thickness of the thin film are measured respectively, and through the formula (where R is the sheet resistance of the thin film, d is the thickness of the thin film), the conductivity of the thin film is calculated to be about 72 S / m. With the help of the near-field / far-field scannable terahertz time-domain spectroscopy system shown in Figure 3 , the time-domain signal at any point on the thin film is collected to measure the time-domain signal and perform Fourier transform. The transmittance spectrum line of Figure 4 shows that the thin film has a high transmittance in the 0.2 - 1 THz broadband range, all greater than 95%. Subsequently, using ultraviolet laser etching technology, the thin film is evenly divided into 16 equal parts along its central angle direction, and a patterned terahertz liquid crystal cell is prepared. The physical diagram of the device is as Figure 5As shown. The liquid crystal used is the HTD028200 model large birefringent liquid crystal produced by Jiangsu HeCheng Display Technology Co., Ltd., with a birefringence coefficient of 0.3 and a liquid crystal layer thickness of 800 μm. By applying different electric fields to 16 different pixel units of the patterned THz liquid crystal transparent electrode, angular spatial encoding is achieved: applying an external voltage of 30 V corresponds to encoding 1; when no external voltage is applied, the liquid crystal main axis is arranged along the y axis direction under the action of the alignment layer, corresponding to encoding 0.

[0017] The present invention adopts specific angular spatial encoding sequences (such as "11110000…", "11001101…", and "10101010…"), divides the transparent electrode into 4 blocks, 8 blocks, and 16 blocks according to angular spatial pixels respectively, and obtains the phase and intensity distribution diagrams as shown in Figure 6 and Figure 7 through near-field measurement. As shown in Figure 4 , clear phase contrasts are presented in different angular spatial pixel regions. In terms of spatial distribution, the spatial field distributions corresponding to the two cases of encoding 0 and 1 are complementary: when the encoding is 1, the phase value is 0; while when the encoding is 0, the phase value is π. In addition, by analyzing the intensity maps corresponding to these encoding sequences, the results show that the transmittance of the graphene electrode exceeds 90%.

[0018] The present invention further verifies the multi-level encoding control process of the patterned THz liquid crystal transparent electrode. As shown in Figure 8 (a), the time delay of the pulse intuitively reflects the phase shift value generated by the device. On this basis, the phase difference spectrogram is obtained through Fourier transform. It should be noted that in the frequency band range of 0.5 - 0.6 THz, the phase difference spectral line is relatively flat. Figure 8 (b) shows the phase differences at 0.55 THz under 5 different level encoding states randomly selected within the wide spectral range. The experimental results show that as the external voltage increases non-linearly, the liquid crystal correspondingly presents five different spatial states, promoting the completion of the five-level encoding process of the phase difference, and its values are 0°, 46°, 87°, 130°, and 179° respectively. To sum up, the patterned THz liquid crystal transparent electrode has both high transmittance and precise angular pixel control ability, and can effectively realize dynamic phase reconstruction.

[0019] In the embodiments provided by the present invention, the systems and methods used can also be implemented in other ways. For example, the patterned pixel units are not limited to the uniform division method of the central angle, and can be any other shape, such as square, strip, V-shaped, etc., or can be a non-uniform division shape; for example, the type and kind of liquid crystal; for example, the thickness and size of the glass substrate; for example, the initial orientation method of the liquid crystal, such as photoalignment technology, applying an external initial magnetic field, etc.; for example, the external field regulation method of the liquid crystal, such as using a breadboard and an alternating voltage source, etc. For example, the direction of the initial alignment layer, such as xoz any direction in the plane, yoz any direction in the plane, etc. For example, the application of the external voltage, the direction of which can be selected along y axis, xoy any direction different from the initial orientation such as 45° in the plane, and the magnitude can also be any value such as 30 V, 60 V, 90 V, etc.; for example, the birefringence phase shift of the liquid crystal cell when the maximum voltage is applied, such as , etc.

Claims

1. A dynamic phase reconstruction technique for a patterned terahertz liquid crystal transparent electrode, the device structure of which includes a patterned graphene transparent thin film positive electrode layer (1), an upper glass substrate (2), an upper alignment layer (3), a liquid crystal layer (4), a lower alignment layer (5), a lower glass substrate (6), and a graphene transparent thin film negative electrode layer (7); wherein, The upper glass substrate (2) and the lower glass substrate (6) are undoped fused silica optical glasses with a thickness of 300 μm to 800 μm and a format of at least 30 mm × 30 mm. The upper alignment layer (3) and the lower alignment layer (5) allow the liquid crystal molecules to be randomly arranged in the plane. xoy The patterned graphene transparent thin film positive electrode layer (1) and the graphene transparent thin film negative electrode layer (7) are porous conductive layers formed by spin-coating a polyvinyl alcohol-graphene mixed solution, which can induce the liquid crystal molecules to be arranged along the z axis direction.

2. The dynamic phase reconstruction technique of the patterned terahertz liquid crystal transparent electrode according to claim 1, characterized in that Weld metal leads on the patterned graphene transparent thin film positive electrode layer (1) and the graphene transparent thin film negative electrode layer (7), and connect them to the PCB circuit board, or directly connect conductive tape. Use a programmable power supply or FPGA to perform spatio-temporal programming on the device to achieve dynamic phase reconstruction with multi-pixel and multi-level encoding.

3. The dynamic phase reconstruction technique of the patterned terahertz liquid crystal transparent electrode according to claim 1, wherein Mix polyvinyl alcohol and graphene in a ratio of 2:1, and use the spin coating method to prepare the graphene transparent thin film negative electrode layer (7); and through the ultraviolet laser direct writing technology, evenly divide the film into 16 equal parts along the central angle direction to prepare the patterned graphene transparent thin film positive electrode layer (1).

4. The dynamic phase reconstruction technique of the patterned terahertz liquid crystal transparent electrode according to claim 1, wherein The thickness of the graphene transparent thin film ≤ 0.5 μm, and the transmittance ≥ 90% in the range of 0.1 - 1 THz; control the degree of graphene oxidation-reduction by drying in a dryer for ≥ 2 h to achieve its conductivity > 50 S / m.

5. The dynamic phase reconstruction technique of the patterned terahertz liquid crystal transparent electrode according to claim 1, wherein The upper alignment layer (3) and the lower alignment layer (5) are formed by coating a polyimide film on a glass substrate and mechanically rubbing to form micron-scale grooves, thereby inducing the alignment of the intermediate liquid crystal layer (4). The thickness of the liquid crystal layer (4) is 300 μm to 1200 μm, and the birefringence coefficient in the terahertz band Δn is 0.25 to 0.

35.

6. The dynamic phase reconstruction technique of the patterned terahertz liquid crystal transparent electrode according to claim 1, characterized in that, For the patterned graphene transparent thin film positive electrode layer (1), m different pixel units are respectively applied with different voltages for angular space encoding. Among them, the encoding method with a voltage of 30 V to 50 V is called encoding 1, and the corresponding phase value is 0. The encoding method without applying voltage is called encoding 0, and the corresponding phase value > 0. Since each pixel unit has two encoding methods, the entire patterned terahertz liquid crystal transparent electrode has a total of 2 m adjustable phase arrangement methods.

7. The dynamic phase reconstruction technique of the patterned terahertz liquid crystal transparent electrode according to claim 1, wherein The single pixel of the patterned graphene transparent thin film positive electrode layer (1) can be upgraded from 1-bit coding to multi-level coding. If voltages with n different intensities are applied to the pixel unit, finally 2×n m adjustable phase arrangement modes can be achieved.

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