Laser direct writing reconfigurable terahertz polarization device and preparation method thereof

Abstract

The invention belongs to the technical field of terahertz polarization devices, and particularly discloses a laser direct writing reconfigurable terahertz polarization device and a preparation method thereof. The preparation method comprises the following steps: sputtering a phase change material layer on one surface or two opposite surfaces of a substrate by adopting a magnetron sputtering process; and inducing a partial region of the phase-change material in the phase-change material layer to be converted from an amorphous state to a crystalline state by scanning nanosecond laser pulses at a high speed, and controlling a laser track through a galvanometer scanning system to print a grating structure so as to obtain the terahertz polarization device. The preparation method has the characteristics of no photoetching and high preparation efficiency, and the extinction ratio of the prepared terahertz polarization device is high.

Description

Technical Field

[0001] This application belongs to the field of terahertz polarization device technology, and more specifically, relates to a laser-written reconfigurable terahertz polarization device and its fabrication method. Background Technology

[0002] Terahertz polarization devices are the core functional components of terahertz systems. They are used to control the polarization state of terahertz waves and are key supporting components in fields such as terahertz imaging, material detection, and communication.

[0003] In related technologies, traditional polarization device fabrication techniques face significant limitations. For example, the mainstream production methods for polarization devices rely on a series of traditional micro-nano fabrication techniques (photolithography, ion etching, etc.). These techniques are not only complex and costly, but also have relatively long production cycles, making it difficult to achieve large-scale, high-efficiency, and large-size production of polarization devices. Although some production solutions attempt to simplify the process, they often struggle to achieve an ideal balance between improving production efficiency and controlling the extinction ratio, failing to meet the dual requirements of performance and mass production in practical applications. Therefore, improvements are urgently needed. Summary of the Invention

[0004] To address the shortcomings or improvement needs of existing technologies, this application provides a laser-written reconfigurable terahertz polarization device and its fabrication method, aiming to improve the problem that traditional polarizer fabrication methods are difficult to achieve high-efficiency production of polarization devices with high extinction ratios.

[0005] This application provides a method for fabricating a laser-written reconfigurable terahertz polarization device, comprising the following steps: A phase change material layer is formed on one or both opposite sides of a substrate using a deposition process; A terahertz polarization device is obtained by inducing a portion of the phase change material in the phase change material layer to transform from an amorphous state to a crystalline state using a high-speed scanning nanosecond laser pulse, and then printing a grating structure by controlling the laser trajectory through a galvanometer scanning system.

[0006] As a further preferred embodiment, the substrate is a low-refractive-index substrate adapted to the transmission of terahertz waves and microwaves.

[0007] As a further preferred option, the substrate is made of TPX or high-resistivity silicon material.

[0008] As a further preferred embodiment, the thickness of the substrate is 0.2 mm to 50 mm.

[0009] As a further preferred embodiment, the thickness of the phase change material layer is 100nm~400nm.

[0010] As a further preferred embodiment, the phase change material layer is a reversible phase change writable medium.

[0011] As a further preferred embodiment, the phase change material layer adopts a combination of one or more materials including InSbTe series phase change materials and GeSbTe series phase change materials.

[0012] As a further preferred embodiment, when a portion of the phase change material in the phase change material layer is induced to change from an amorphous state to a crystalline state by a high-speed scanning nanosecond laser pulse, and a grating structure is printed by controlling the laser trajectory through a galvanometer scanning system, the spot diameter is 15µm~30µm, the scanning speed is 0.1m / s~1.5m / s, the repetition frequency is 40kHz~400kHz, the pulse width is 5ns~80ns, and the duty cycle is 0.7~0.9.

[0013] The second aspect of this application provides a laser-written reconfigurable terahertz polarization device using the following technical solution: A laser-written reconfigurable terahertz polarization device is prepared based on any of the preparation methods described in the first aspect.

[0014] As a further preferred embodiment, the terahertz polarization device has a one- or two-sided grating structure.

[0015] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages: The terahertz polarization device of this application consists of a phase change material layer and a substrate. A grating structure is fabricated by modifying the phase change material using a high-speed processing system, resulting in the reflection of TE polarized light and high transmission of TM polarized light, thus giving the transmitted light strong linear polarization characteristics. This technique enables the efficient fabrication of high-efficiency, high-extinction-ratio, and large-size terahertz-microwave polarization devices without photolithography. In particular, this method achieves patterning through only deposition (such as magnetron sputtering) and galvanometer-based laser scanning, and supports single-sided or double-sided grating processing in one or two steps, enabling high-volume production of high-performance polarization devices. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating a method for fabricating a laser-written reconfigurable terahertz polarization device according to an embodiment of this application. Figure 2 This is a schematic diagram of the processing system provided in the embodiments of this application; Figure 3 These are optical microscope images of the terahertz polarization device provided in the embodiments of this application; Figure 4 This is a transmittance image of a terahertz polarization device with a single-layer grating structure provided in an embodiment of this application; Figure 5This is a transmittance image of a terahertz polarization device with a double-layer grating structure provided in the embodiments of this application; Figure 6 This is a comparison diagram of the extinction ratios of single and double-layer terahertz polarization devices provided in the embodiments of this application; Figure 7 This is a schematic diagram of an imaging system that includes the terahertz polarization device of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] The following is in conjunction with the appendix Figures 1-7 This application will be described in further detail.

[0019] This application discloses a method for fabricating a laser-written reconfigurable terahertz polarization device. (Refer to...) Figure 1 The preparation method includes the following steps: A phase change material layer is formed on one or both sides of a substrate using a deposition process; a portion of the phase change material in the layer is induced to change from an amorphous state to a crystalline state by a high-speed scanning nanosecond laser pulse, and a grating structure is printed by controlling the laser trajectory through a galvanometer scanning system to obtain a terahertz polarization device.

[0020] The substrate is preferably a low-refractive-index substrate suitable for the transmission of terahertz waves and microwaves; that is, the substrate is a low-refractive-index transparent substrate in the THz-microwave band. With this design, the substrate has high transmittance (generally not less than 70%) for electromagnetic waves in the terahertz to microwave band, and the substrate material has a low refractive index (generally not higher than 3.5). The purpose of this design is to reduce the reflection loss of electromagnetic waves on the material surface, significantly improve the transmission efficiency in the terahertz to microwave band, thereby improving the performance of terahertz polarization devices. Simultaneously, the low refractive index design enhances the extinction ratio, further improving the polarization purity and optical contrast of the device.

[0021] In some specific embodiments, the substrate is made of materials such as TPX or high-resistivity silicon. The substrate thickness is preferably 0.2 mm to 50 mm. This range satisfies the mechanical strength requirements of the device while avoiding terahertz wave propagation delay and energy attenuation caused by excessive thickness. When the substrate thickness is less than 0.2 mm, the processing window is easily reduced, the material is prone to burning, and the extinction ratio performance of the polarization device is also easily reduced. When the thickness exceeds 50 mm, the electromagnetic wave propagation path is significantly increased, causing phase mismatch and a decrease in transmittance. Therefore, controlling the substrate within this preferred range helps to achieve synergistic optimization of high transmittance, high extinction ratio, and good mechanical stability, providing ideal conditions for subsequent laser-written high-precision grating structures.

[0022] The phase change material layer is preferably a reversible phase change writable medium. A reversible phase change writable medium means that the medium can undergo a reversible transition between at least two phase states under the action of an external excitation signal, and the phase transition causes the phase change material to produce identifiable differences in physical properties, based on these differences in physical properties, to realize the writing, erasing and repeated rewriting of information.

[0023] In some embodiments, a writable medium capable of reversible transitions between amorphous and crystalline states is preferably used, and erasure and rewriting are achieved by thermal, optical, or electro-induced reset in order to maintain the target polarization performance and allow for multiple cycles.

[0024] In some embodiments, the phase change material layer comprises one or more materials selected from InSbTe series phase change materials (i.e., IST-based), GeSbTe series phase change materials (i.e., GST-based), or other reversible phase change / writable media. In actual fabrication, InSbTe series phase change materials are preferred, and In3SbTe2 is even more preferred.

[0025] The InSbTe series of phase change materials is preferred because these materials have higher electrical conductivity. To achieve high polarization extinction ratios, GST materials often require greater thickness, but the depth of laser-written phase transitions is limited, which introduces practical processing difficulties and affects the fabrication process. Therefore, the InSbTe series of materials is the preferred choice.

[0026] In some specific embodiments, the thickness of the phase change material layer is 100 nm to 400 nm. This thickness range ensures that the phase change material fully responds to phase change induction during laser direct writing, while avoiding problems such as uneven coverage due to excessive thinness or incomplete crystallization due to excessive thickness.

[0027] The preferred deposition process is magnetron sputtering. Magnetron sputtering is used to treat one or both opposite sides of the substrate, with the phase change material (PCM) serving as the target for sputtering the PCM layer. This allows for the deposition of a PCM thin film on the substrate, which is the PCM layer. Before processing the substrate using magnetron sputtering, it is typically necessary to clean and dry the substrate.

[0028] In some embodiments, a portion of the phase change material in the phase change material layer is induced to change from an amorphous state to a crystalline state by a high-speed scanning nanosecond laser pulse. The laser wavelength is preferably 1064 nm, the spot diameter is 15 μm to 30 μm, the scanning speed is 0.1 m / s to 1.5 m / s, the repetition frequency is 40 kHz to 400 kHz, the pulse width is 5 ns to 80 ns, and the duty cycle is 0.7 to 0.9.

[0029] In this design, a 1064nm nanosecond laser source was selected. Compared to the 800nm ​​laser source commonly used in the industry, the 1064nm laser chosen in this design has stronger material penetration and better thermal effect control characteristics, which can effectively reduce the risk of surface ablation and improve the uniformity and boundary clarity of the phase transition region. At the same time, this wavelength matches well with the absorption characteristics of the substrate selected in this application, reducing energy loss while ensuring processing accuracy, further improving processing efficiency and device performance consistency, and providing a reliable technical path for the large-scale integration of terahertz polarization devices.

[0030] In particular, the phase transition region induced by a 1064nm laser wavelength will have higher geometric accuracy and interface sharpness. Combined with the high-speed scanning capability of the galvanometer system, this method can achieve high-efficiency and stable fabrication of polarization devices and precise control of polarization response characteristics in the terahertz band. Simultaneously, the 1064nm light source and the electronic transition energy levels of the phase transition material are better matched, improving energy utilization efficiency, making the crystallization process more controllable, and ensuring stable birefringence and low insertion loss of the device over a wide frequency range.

[0031] By selecting a spot diameter of 15µm to 30µm, the range of the heat-affected zone can be effectively controlled while ensuring sufficient energy density, avoiding thermal crosstalk between adjacent areas, thereby improving the device integration density and functional reuse capability.

[0032] The scanning speed of 0.1 m / s to 1.5 m / s ensures sufficient laser irradiation time while balancing processing efficiency and morphological control of the phase transition region, avoiding heat accumulation problems caused by incomplete crystallization due to excessively fast scanning or excessively slow scanning. Combined with a repetition frequency of 40 kHz to 400 kHz and a pulse width of 5 ns to 80 ns, precise pulse superposition and thermal field control can be achieved, further improving phase transition uniformity. A duty cycle of 0.7 to 0.9 ensures the continuity and stability of energy input, which is beneficial for forming high-quality crystalline regions and enhances the consistency and repeatability of terahertz wave manipulation performance.

[0033] In some embodiments, the high-speed processing system preferably includes a high-precision, high-speed beam deflection mechanism, which controls the laser beam to scan the target area quickly and accurately along a preset path (i.e., galvanometer laser scanning) to achieve rapid forming of the grating structure.

[0034] like Figure 2 As shown, in some embodiments, the high-speed processing system includes a nanosecond laser source, a beam expander, a galvanometer scanner, and a planar focusing lens. The galvanometer scanner includes an X-axis galvanometer and a Y-axis galvanometer, which are driven to rotate by corresponding high-speed motors. In use, the laser emitted by the nanosecond laser source is shaped by the beam expander... In practical applications, a nanosecond laser source emits a nanosecond laser beam. This beam is expanded by a beam expander and then enters a galvanometer scanner, where it is deflected and adjusted. The beam then passes through a flat-field focusing lens and is transmitted to the sample (i.e., a substrate with a phase change material layer on its surface) to form a light spot, inducing a phase transition in the phase change material layer. During this process, a high-speed motor drives the X-axis and Y-axis galvanometers to adjust their angles, thereby adjusting the path of the light spot. This allows the light spot to scan along a specific pattern on the sample (such as parallel stripes of equal width and spacing).

[0035] Under this design, patterning is completed only through deposition (such as magnetron sputtering) and galvanometer-based laser scanning. It supports one- or two-stage processing of single-sided or double-sided grating structures (e.g., processing only one side, processing both sides simultaneously or in stages), enabling the efficient fabrication of high-efficiency, high-extinction-ratio, and large-size terahertz-microwave polarization devices without photolithography. In particular, by processing the substrate on both sides, terahertz polarization devices with double-sided grating structures (i.e., double-sided coating) can be fabricated, significantly improving the extinction ratio of the terahertz polarization device. Furthermore, device erasure and rewriting are achieved through thermal / optical / electro-induced reset, maintaining the target polarization performance and allowing for multiple cycles.

[0036] Under this design, the obtained device consists of a phase change material layer and a substrate. After the phase change material is modified using a high-speed processing system to prepare the grating structure, TE polarized light is reflected and TM polarized light is highly transmitted, thus giving the transmitted light a strong linear polarization characteristic.

[0037] In current mainstream designs, a dual-axis displacement stage is often used to move the sample to control the laser scanning path. However, research has found that dual-axis displacement stages are limited by mechanical inertia, making it difficult to increase processing speed and prone to introducing positioning errors. They are mostly used in applications with small scanning areas, resulting in extremely small device sizes. In contrast, this solution uses a galvanometer scanner driven by a high-speed motor. It eliminates the need to move the sample, achieving rapid scanning of the laser spot on the phase change material layer solely through optical deflection. This significantly improves processing efficiency and accuracy while reducing system complexity and vibration interference, making it more suitable for the mass production of large-area (sizes up to 5cm×5cm, 20cm×20cm, or even larger) and highly uniform terahertz polarization devices.

[0038] Furthermore, leveraging the high scanning response frequency and low inertia of the galvanometer, this design enables high-speed and precise deflection of the laser spot, further enhancing the fabrication accuracy and consistency of the grating structure. Combining the high repetition rate and short pulse width of the nanosecond laser, local crystallization or amorphization of the phase change material can be efficiently induced without damaging the substrate, thereby forming a clear periodic grating structure. Therefore, this approach not only simplifies the fabrication process but also significantly reduces reliance on complex photolithography, making it suitable for mass production of high-performance terahertz-microwave polarization devices.

[0039] Example 1: A method for fabricating a terahertz polarization device includes: Step 1: Select a TPX substrate with a thickness of 0.5mm and a diameter of 2 inches, and clean and dry it.

[0040] Step 2: A thin film of phase change material In3Sb1Te2 is sputtered onto the cleaned substrate using magnetron sputtering. The target and substrate are placed before sputtering. Sputtering conditions: Base vacuum: 8 × 10⁻⁶ -5 Pa, DC18 W, Ar flow rate of 20 sccm, sputtering rate of 80 nm / 600 s, total sputtering time of 750 s, thickness of 100 nm, other parameters are not specifically limited.

[0041] Step 3: High-speed scanning nanosecond laser pulses are used to irradiate the amorphous phase change material layer to induce a phase change in the region. The laser trajectory is controlled by galvanometer scanning to print the grating structure. The spot diameter is approximately 20 μm, the scanning speed is 0.25 m / s, the repetition frequency is 80 kHz, the pulse width is 30 ns, the scanning area is 5 cm × 5 cm, and other parameters are not specifically limited.

[0042] like Figure 3 The image shown is an optical microscope image of a fabricated terahertz polarization device. The white area represents laser-induced crystalline IST, and the gray area represents amorphous IST. In this embodiment, the crystalline IST has a width of approximately 15 μm and a grating period of 20 μm.

[0043] like Figure 4 The image shown illustrates the transmittance of the terahertz polarization device with a single-layer grating structure fabricated in this embodiment. Figure 4 In the figure (A), it is a software simulation diagram of the transmittance of terahertz polarization devices, where a represents laser-induced crystalline IST and c represents amorphous IST. Figure 4 (B) in the figure shows the experimental test results for the transmittance of the terahertz polarization device. As can be seen, the terahertz polarization device designed in this paper can reflect TE polarized light and transmit TM polarized light at high speed, thus giving the transmitted light a strong linear polarization characteristic.

[0044] Example 2: The difference between this embodiment and Embodiment 1 is that, in step 2 of this embodiment, two layers of phase change material In3Sb1Te2 thin films are sputtered onto the substrate. That is, IST is deposited on both sides of the substrate to prepare a double-layer grating structure, thereby further improving the polarization performance of the device.

[0045] like Figure 5 The image shown illustrates the transmittance of the terahertz polarization device with a double-layer grating structure fabricated in this embodiment. Figure 5 (A) in the figure is a software simulation diagram of the transmittance of a terahertz polarization device. Figure 5 (B) in the image is an experimental test graph related to the transmittance of terahertz polarization devices. The two lines in the image indicate the type and... Figure 4 Similarly, these refer to TE-polarized light and TM-polarized light, respectively. It is evident that the terahertz polarization device in this design enables TE-polarized light to be reflected and TM-polarized light to be highly transmitted, thus giving the transmitted light a strong linear polarization characteristic.

[0046] Furthermore, Figure 6The diagram shows a comparison of the extinction ratios of the terahertz polarization device with a single-layer grating structure mentioned in Example 1 and the terahertz polarization device with a double-layer grating structure mentioned in Example 2. It is clearly visible that the double-layer design significantly enhances the extinction ratio (approximately doubling it compared to the single-layer design). Within a wide frequency range of 0-2 THz, both grating structures exhibit good extinction ratios, with the double-layer grating structure showing a significantly higher extinction ratio than the single-layer grating structure. It can be clearly seen that in this experimental simulation, the extinction ratio of the single-layer grating structure reaches 20 dB, while the double-layer structure improves the extinction ratio by approximately 20 dB compared to the single-layer structure. The double-sided coating design further enhances the extinction ratio of the polarization device.

[0047] Furthermore, Figure 7 A schematic diagram of a THZ polarization imaging system incorporating the polarization device of this application is shown. Specifically, Figure 7 Figure 'a' shows the schematic diagram of the imaging system; that is, after the laser passes through the terahertz polarization device (IST polarization device) of this application, it is focused by the parabolic mirror and passes through the imaging sample before entering the subsequent Golay detector for imaging. Figure 7 In the graph, 'b' represents the probe power curve corresponding to the angle between the polarization direction of the light source and the direction of the IST grating lines. Figure 7 The radiation pattern of the probe light power corresponding to the angle between the polarization direction of the c-source light source and the direction of the IST grating line. Figure 7 The value 'd' in the figure represents the intensity of the imaged sample at different angles. It can be seen that the probe power exhibits periodic changes as the angle between the polarization direction of the light source and the direction of the IST grating lines changes, and the imaging contrast reaches its optimum at a specific angle. This verifies the ability of this polarization device to efficiently control the polarization state in the terahertz band. Therefore, the terahertz polarization device of this application is suitable for THZ polarization imaging systems and has excellent application value.

[0048] It should be understood that expressions such as "comprising" and "may include" as used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "comprising" and / or "having" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but should not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0049] It should be understood that the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0050] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0051] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0052] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fabricating a laser-written reconfigurable terahertz polarization device, characterized in that, Includes the following steps: A phase change material layer is formed on one or both opposite sides of a substrate using a deposition process; A terahertz polarization device is obtained by inducing a portion of the phase change material in the phase change material layer to transform from an amorphous state to a crystalline state using a high-speed scanning nanosecond laser pulse, and then printing a grating structure by controlling the laser trajectory through a galvanometer scanning system.

2. The preparation method according to claim 1, characterized in that, The substrate is a low-refractive-index substrate adapted to the transmission of terahertz waves and microwaves.

3. The preparation method according to claim 1, characterized in that, The substrate is made of TPX or high-resistivity silicon material.

4. The preparation method according to claim 1, characterized in that, The thickness of the substrate is 0.2mm to 50mm.

5. The preparation method according to claim 1, characterized in that, The thickness of the phase change material layer is 100nm~400nm.

6. The preparation method according to claim 1, characterized in that, The phase change material layer is a reversible phase change writable medium.

7. The preparation method according to claim 6, characterized in that, The phase change material layer is a combination of one or more of the InSbTe series phase change materials and the GeSbTe series phase change materials.

8. The preparation method according to any one of claims 1-7, characterized in that, When a portion of the phase change material in the phase change material layer is induced to change from an amorphous state to a crystalline state by a high-speed scanning nanosecond laser pulse, and a grating structure is printed by controlling the laser trajectory through a galvanometer scanning system, the spot diameter is 15um~30um, the scanning speed is 0.1m / s~1.5m / s, the repetition frequency is 40kHz~400kHz, the pulse width is 5ns~80ns, and the duty cycle is 0.7~0.

9.

9. A laser-written reconfigurable terahertz polarization device, prepared according to the fabrication method described in any one of claims 1-8.

10. The terahertz polarization device as described in claim 9, characterized in that, This terahertz polarization device has a one- or two-sided grating structure.

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