Active modulation of flexible dual-channel switchable terahertz modulator

Abstract

This invention discloses an actively modulated flexible dual-channel switchable terahertz modulator, which consists of a flexible substrate and a metasurface structure. The flexible substrate is made of polyimide, and the metasurface structure is composed of vanadium dioxide and metallic materials, forming a vertical "I"-shaped periodic pattern with a period size of 120 μm × 120 μm, a minimum side length of 10 μm for each pattern unit, and a metasurface structure thickness of 200 nm. The phase transition between the insulating and metallic states of vanadium dioxide is achieved through external temperature control. This invention realizes the function of low-temperature full transmission and high-temperature dual-resonance dynamic switching in the 0.1–2 THz frequency band, and can be applied to dynamic switching devices in the terahertz band.

Description

Technical Field

[0001] This invention relates to the field of dynamic control technology in the terahertz band, specifically to an actively controllable flexible dual-channel switchable terahertz modulator. Background Technology

[0002] Vanadium dioxide (VO2) is a high-performance functional material that undergoes a reversible phase transition from an insulating to a metallic state at approximately 68°C, accompanied by significant changes in conductivity and dielectric constant. In the terahertz band, the phase transition of VO2 allows for dynamic control of electromagnetic wave transmission, reflection, and absorption, making it an ideal material for dynamic modulation. Through external stimuli (such as temperature, light, or electric fields), the phase transition of VO2 can achieve rapid response and reversible switching, providing a solid technical foundation for the development of dynamic terahertz modulation devices.

[0003] Metasurfaces are two-dimensional artificial materials designed using subwavelength structural units, significantly improving the modulation depth and bandwidth coverage of target frequency bands. Combining the dynamic phase transition characteristics of VO2 with dual-resonant metasurface design enables efficient dynamic modulation in the terahertz band. Furthermore, the introduction of flexible materials allows the device to adapt to complex bending and deformation environments, thereby enhancing its practicality and adaptability to various scenarios.

[0004] Nevertheless, challenges remain in the structural optimization, flexible design, and control performance of VO2-based terahertz control devices. For example, how to further improve resonance performance through structural design, how to achieve stable integration of VO2 phase change materials on flexible substrates, and how to reduce the metallic state loss of VO2 are still problems that urgently need to be solved. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide an actively modulated flexible dual-channel switchable terahertz modulator, which improves the modulation depth and integration by combining VO2 material with a flexible dual-resonant metasurface, thereby solving the problems existing in the background technology.

[0006] Technical solution: The present invention discloses an actively modulated flexible dual-channel switchable terahertz modulator, comprising a flexible substrate layer and a metasurface structure. The flexible substrate layer is composed of polyimide material; the metasurface structure is composed of vanadium dioxide and metallic materials, forming a vertical "I"-shaped periodic pattern. The phase transition between the insulating and metallic states of vanadium dioxide is achieved by external temperature control (20 ℃~87 ℃).

[0007] Furthermore, the period size is 120 μm × 120 μm.

[0008] Furthermore, the metasurface structure has a thickness of 200 nm; the minimum side length of the "I"-shaped periodic pattern unit is 10 μm.

[0009] Furthermore, in the low-temperature insulating state, the modulator exhibits high transmission efficiency in the 0.1–2 THz frequency band, with a transmittance close to 0 dB.

[0010] Furthermore, when the modulator is in a high-temperature metallic state, vanadium dioxide couples with the metal structure to form a dual-resonance characteristic, generating two resonance valleys with resonant frequencies of 0.604 THz and 1.65 THz, respectively. The first resonance has a 3dB bandwidth of 0.302-0.923 THz, a center frequency of 0.604 THz, and a quality factor of 6.41. The second resonance has a 3dB bandwidth of 1.362-1.947 THz, a center frequency of 1.65 THz, and a quality factor of 14.62, thus realizing the dual-resonance dynamic switching control function in the terahertz band.

[0011] Furthermore, the modulation depth of the switch at the two resonant frequency points is calculated using the following formula: ; Where M is the relative modulation depth. This represents the maximum transmittance of the device in the dielectric state. This represents the minimum transmittance of the device in its metallic state.

[0012] Furthermore, for the polyimide dielectric layer, the thickness is 5 μm, and its relative permittivity is set to 3.5 +0.0027i.

[0013] The present invention discloses a design method for an actively modulated flexible dual-channel switchable terahertz modulator, comprising the following steps: (1) Design of flexible substrate and metasurface structure: The flexible substrate is made of polyimide material; the metasurface structure is composed of vanadium dioxide and metal material to form a vertical "I" shaped periodic pattern with a period size of 120 μm × 120 μm and a minimum side length of 10 μm for each "I" shaped periodic pattern unit; the thickness of the metasurface structure is 200 nm. (2) Design an external temperature (20 ℃~87 ℃) control system to achieve the phase transition of vanadium dioxide from the insulating state to the metallic state; (3) The electromagnetic response characteristics of the flexible switchable dual-resonance terahertz filter metasurface structure were simulated and analyzed using electromagnetic full-wave simulation software. The boundary conditions in the x and y directions were set as periodic boundaries, while the z direction was set as an open boundary. By setting a plane wave port, the linearly polarized electromagnetic wave was made to propagate along the z-axis and be incident perpendicularly from the +z axis to the top layer region of the metasurface structure. The transmittance was monitored using an electric field probe. The simulation frequency range covered 0.1-2 THz, and the time-domain transmission line matrix method was used for calculation.

[0014] This invention discloses an application method for an actively modulated flexible dual-channel switchable terahertz modulator, applied to dynamic switching devices in the terahertz band. The dynamic switching device, combining the phase transition characteristics of vanadium dioxide and a dual-resonant metasurface design, can achieve low-temperature full transparency and high-temperature dual-resonant switching functions within the 0.1-2 THz frequency band through temperature control. At low temperatures, the emissivity is close to 0 dB; while at high temperatures, it transforms into a metallic state, forming two resonance valleys with resonant frequencies of 0.604 THz and 1.65 THz through coupling with a metallic pattern.

[0015] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: The device of this invention achieves functional switching from high-efficiency transmission (low-temperature dielectric state) to dual-resonant switching (high-temperature metallic state) within the 0.1-2 THz frequency band by adjusting the ambient temperature. Specifically, the low-temperature insulating state exhibits high transmission characteristics within the 0.1-2 THz range, while the high-temperature metallic state forms two significant resonance valleys, demonstrating precise switching control. Utilizing the reversible phase transition characteristics of vanadium dioxide, the device can flexibly switch between high transmission and dual-resonant switching functions, enriching the dynamic control methods in the terahertz band and providing a new research direction for terahertz metasurface technology. The transmission structure combined with temperature control design greatly simplifies the control mechanism and improves the device's flexibility and ease of use, adapting to various application scenarios. The flexible design and polarization-independent characteristics of this invention further expand the device's applicability in complex environments, enabling its widespread application in terahertz communication, sensing, and imaging fields. Attached Figure Description

[0016] Figure 1 These are schematic diagrams of the structure and dimensions of the present invention; Figure 2 The flexible dual-channel switchable terahertz switching device of this invention achieves the effect of dual resonance and full transmission function switching: when vanadium dioxide is in a high-temperature metallic state (conductivity of 200,000 S / m), its filtering characteristics are as follows: Figure 2 As shown in (a), the minimum transmittance is close to -30 dB, indicating a significant filtering effect of the device at the resonant frequency, while also exhibiting polarization independence. However, when vanadium dioxide is in a low-temperature dielectric state (conductivity 200 S / m), the transmittance is as follows... Figure 2 As shown in (b), the transmittance remains almost 0 dB, and the device exhibits near-full transparency in the 0.1–2 THz range; Figure 3 This describes the effect of temperature on the transmittance of the flexible dual-channel switchable terahertz switching device of the present invention. Figure 4The transmittance (dB) of the flexible dual-channel switchable terahertz switching device of this invention is as follows: The first resonance, obtained when vanadium dioxide is in a high-temperature metallic state, has a 3dB bandwidth of 0.302-0.923 THz, a bandwidth of 0.621 THz, a center frequency of 0.604 THz, and a quality factor of 6.41. The second resonance has a 3dB bandwidth of 1.362-1.947 THz, a bandwidth of 0.585 THz, a center frequency of 1.65 THz, and a quality factor of 14.62. Figure 5 This is a schematic diagram of the flexible dual-channel switchable terahertz switching device system based on vanadium dioxide (VO2) of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0018] Example 1: Flexible Dual-Channel Switchable Terahertz Switching Device Based on Vanadium Dioxide (VO2) This invention proposes a transmissive, temperature-controlled dual-resonant filtering terahertz switching device based on vanadium dioxide. This device utilizes the properties of vanadium dioxide to achieve multiple functions under different temperature conditions. At low temperatures, vanadium dioxide is in an insulating state, exhibiting excellent dielectric properties. The device achieves high-efficiency transmission in the 0.1–2 THz frequency band with almost no additional attenuation. This feature is suitable for terahertz systems requiring high transmittance, such as unobstructed transmission paths in terahertz imaging and communications.

[0019] Under high-temperature conditions, vanadium dioxide undergoes a phase transition, transforming into a metallic state. At this point, the device couples with the metallic pattern, forming two significant resonance valleys, exhibiting dual-resonance filtering characteristics and effectively suppressing terahertz waves in specific frequency bands (0.604 THz and 1.65 THz). This function can be used as a tunable bandstop filter to achieve selective switching and suppression of signals at specific frequencies.

[0020] In the embodiments of this invention, the electromagnetic response characteristics of the flexible switchable dual-resonant terahertz filter metasurface structure were analyzed in detail using electromagnetic full-wave simulation software. During the simulation, the boundary conditions in the x and y directions were set as periodic boundary conditions, while the z direction adopted an open boundary with additional space to simulate the electromagnetic wave propagation environment in infinite space. By setting a plane wave port, linearly polarized electromagnetic waves propagated along the z-axis and were incident perpendicularly onto the top layer region of the metasurface structure from the +z-axis. The transmittance was monitored using an electric field probe. The simulation frequency range covered 0.1-2 THz, and the time-domain transmission line matrix method was used for calculation.

[0021] This metasurface structure exhibits high polarization independence, demonstrating excellent stability under both TE and TM polarization, and retains good active regulation performance during temperature switching. The designed structure possesses superior stability and environmental adaptability, providing broad prospects for practical engineering applications.

[0022] Example 2: Performance Calculation of Flexible Dual-Channel Switchable Terahertz Switch Based on Vanadium Dioxide (VO2) This invention proposes a transmissive, temperature-controlled, flexible, switchable bandstop terahertz filter and switch device. Its unit structure employs a periodic design with a period size of 120 μm × 120 μm. The device is based on a double-layer metasurface structure, and its main components include: Bottom dielectric layer: A 5 μm thick polyimide material is used, which possesses excellent dielectric properties and provides structural stability and good transmission characteristics. Furthermore, polyimide exhibits low loss characteristics in the terahertz band, making it an ideal metasurface substrate material.

[0023] Top structural layer: Composed of aluminum (Al) and vanadium dioxide (VO2), with a thickness of approximately 200 nm. The top structure adopts a checkerboard design, in which the minimum side length of the checkerboard unit is 10 μm. Through periodic arrangement and design, it achieves precise control and flexible response in the terahertz band.

[0024] In the simulation analysis, the embodiments of the present invention used simulation software to verify and optimize the characteristics of the device. For the polyimide dielectric layer, its relative permittivity was set to 3.5 + 0.0027i, taking into account the dielectric properties and loss factor of polyimide.

[0025] In embodiments of the present invention, when the device is under low-temperature conditions, vanadium dioxide (VO2) remains in an insulating state, exhibiting excellent dielectric properties. In this state, the device possesses high-efficiency transmission performance in the 0.1–2 THz frequency band, with near-full transmittance and almost no additional attenuation loss.

[0026] Under high-temperature conditions, vanadium dioxide undergoes a phase transition, changing from an insulating state to a metallic state. At this point, the metallic pattern in the device structure interacts with the conductivity of vanadium dioxide, forming a coupling effect. This generates significant resonance valleys at specific frequency points (0.604 THz and 1.65 THz), exhibiting remarkable double-resonant switching characteristics. This function effectively suppresses terahertz wave transmission in a specific frequency band, enabling it to function as a tunable bandstop filter, achieving selective switching and suppression of terahertz signals within a target frequency range.

[0027] By adjusting the ambient temperature, this embodiment of the invention enables the device to switch between two states: low-temperature high-transmittance and high-temperature dual-resonant switching. This temperature-adjustable characteristic gives the device active control capabilities, allowing it to respond quickly to actual application requirements and achieve dynamic switching and frequency band control in the terahertz band. This function is applicable to dynamic terahertz communication systems, tunable filtering equipment, and other terahertz technology fields requiring flexible control.

[0028] The device structure design in this embodiment of the invention achieves polarization-independent response characteristics to terahertz waves. Specifically, the device exhibits consistent electromagnetic response performance for both TE-polarized and TM-polarized terahertz incident waves, remaining stable in both transmission and switching states. This characteristic enables the device to operate effectively under complex polarization conditions, expanding its application range and making it suitable for the terahertz wave manipulation requirements of multi-polarized optical fields.

[0029] The device structure design utilizes a 5 μm thick flexible polyimide substrate, providing excellent flexibility and mechanical stability. This flexible design allows the device to adapt to surfaces of various shapes, exhibiting good bending adaptability and reliability. Furthermore, the overall device structure is lightweight, making it easy to integrate into portable and wearable devices, and it can be widely used in flexible terahertz sensing systems and other terahertz applications across multiple scenarios.

[0030] In embodiments of the present invention, the performance parameters of a flexible dual-channel switchable terahertz switch based on vanadium dioxide (VO2) were analyzed and calculated in detail using electromagnetic simulation. Simulation results show that the device exhibits significant dual-resonance characteristics in the high-temperature metallic state. Resonance valleys appear at two frequency points, 0.604 THz and 1.65 THz, with corresponding quality factors Q values ​​of 6.41 and 14.62, respectively, indicating higher frequency selectivity in the second resonance. Calculations show that the bandwidths of these two resonance valleys are 0.449 THz and 0.386 THz, demonstrating the device's effective modulation capability of terahertz waves over a wide frequency range. Furthermore, the device exhibits extremely high modulation depth at both resonant frequencies, calculated using the following formula: ; Where M is the relative modulation depth. This represents the maximum transmittance of the device in the dielectric state. This represents the minimum transmittance of the device in its metallic state.

[0031] At resonance position 1, the 3dB bandwidth is 0.302-0.923THz, and the relative modulation depth ranges from 80.7% to 98.5% within this 3dB bandwidth. At resonance position 2, the 3dB bandwidth is 1.362-1.947THz, and the relative modulation depth ranges from 35.5% to 94.9%. This indicates that the device has a significant suppression effect on terahertz waves in the high-temperature metallic state, and can achieve dynamic amplitude control in multiple frequency bands.

[0032] In summary, the terahertz device of this invention exhibits highly efficient full transparency in the low-temperature insulating state, while in the high-temperature metallic state, it achieves dual-resonant switching control of a specific frequency by forming two resonant valleys. The device demonstrates excellent performance in resonant quality factor, band-stop bandwidth, and modulation depth, making it suitable for terahertz communication, spectrum management, tunable filtering, and other dynamic control applications.

[0033] Example 3: Flexible Switchable Dual-Resonant Terahertz Modulation Device Based on Vanadium Dioxide (VO2) and Its Working Principle like Figure 5 As shown, this embodiment describes a flexible switchable dual-resonant terahertz modulation device based on vanadium dioxide (VO2) and its working principle. The system mainly includes a transmitter, a receiver, and a dual-resonant modulation module based on VO2 material. The transmitter is responsible for signal generation and modulation, the receiver is responsible for signal reception and reconstruction, and the dual-resonant modulation module is the core device of the entire system.

[0034] The transmitter includes a local oscillator, a frequency doubling and amplification link, an optical pump and temperature control module, and a terahertz antenna. The local oscillator generates the baseband signal, providing a stable and low-noise output. The frequency doubling and amplification link amplifies the baseband signal to generate a high-frequency signal. The optical pump and temperature control module triggers the metal-insulator phase transition of the VO2 material through optical pumping or temperature control, thereby changing its electromagnetic properties to achieve modulation switching. The terahertz antenna transmits the modulated terahertz signal. The transmitter works by generating a baseband signal from the local oscillator, which is then amplified to a high-frequency signal by the frequency doubling and amplification link. The phase transition state of the VO2 device is then controlled by the optical pump or temperature control module. The VO2 device switches between two different resonant modes through dual-resonance characteristics, dynamically modulating the frequency or amplitude of the transmitted signal, which is ultimately transmitted into space by the antenna.

[0035] The receiver consists of a terahertz antenna, a low-noise amplifier, a terahertz detector, a low-frequency amplifier, and a digital demodulation module. The terahertz antenna receives the terahertz signal transmitted from the transmitter. The low-noise amplifier amplifies the received signal with low noise, improving the signal-to-noise ratio. The terahertz detector converts the terahertz signal into a low-frequency baseband signal. The low-frequency amplifier amplifies the down-frequency baseband signal, and finally, the digital demodulation module demodulates and restores the signal information. The receiver works by capturing the terahertz signal with the antenna, amplifying it with low noise, down-frequency processing by the detector, and then reconstructing the information transmitted from the transmitter after amplification and demodulation.

[0036] The core component of the system is a flexible dual-resonant modulation device based on vanadium dioxide (VO2), whose main functions are as follows: First, dynamic frequency switching. The metal-insulator phase transition characteristics of VO2 material enable it to rapidly switch electromagnetic properties under optical pumping or temperature control conditions. Through the dual-resonant structure design, the VO2 device can quickly switch between two resonant frequencies, thereby achieving dynamic control of terahertz signal frequencies. Second, switching modulation. The VO2 device has high-speed switching modulation capabilities, with a metal-insulator phase transition response speed reaching the nanosecond level. The signal can be controlled to turn on and off at the transmitting end, achieving signal modulation. Third, enhanced signal selectivity. The dual-resonant structure gives the VO2 device high selectivity for signals in the target frequency band, effectively suppressing interference signals and improving the system's anti-interference capability. Fourth, flexibility and adaptability. The VO2 device is integrated on a flexible substrate, allowing it to maintain stable electromagnetic performance even under mechanical deformation (such as bending or stretching), which provides possibilities for its application in flexible electronic devices and wearable devices.

[0037] By coordinating the transmitting and receiving ends and combining a dual-resonant modulator based on VO2 material, the system can achieve efficient modulation and transmission of terahertz signals. The VO2 flexible switchable dual-resonant terahertz modulator, as the core of the system, not only enables dynamic frequency switching but also performs high-speed modulation and signal selection, providing a flexible and efficient solution for terahertz communication, imaging, and sensing.

Claims

1. An actively modulated flexible dual-channel switchable terahertz modulator, characterized in that, The flexible substrate is made of polyimide material; the metasurface structure is composed of vanadium dioxide and metal materials, forming a vertical "I"-shaped periodic pattern. The phase transition between the insulating and metallic states of vanadium dioxide is achieved by controlling the external temperature from 20 ℃ to 87 ℃. The external temperature ranges from 20°C to 87°C; the periodic dimension... The surface area is 120 μm × 120 μm; the thickness of the metasurface structure is 200 nm; the minimum side length of the "I"-shaped periodic pattern unit is 10 μm; in the low-temperature insulating state, the modulator exhibits high transmission efficiency in the 0.1-2 THz frequency band, with a transmittance close to 0 dB; In the high-temperature metallic state, the modulator exhibits dual-resonance characteristics through the coupling of vanadium dioxide with the metallic structure, generating two resonance valleys with resonant frequencies of 0.604 THz and 1.65 THz. The first resonance has a 3dB bandwidth of 0.302–0.923 THz, a center frequency of 0.604 THz, and a quality factor of 6.

41. The second resonance has a 3dB bandwidth of 1.362–1.947 THz, a center frequency of 1.65 THz, and a quality factor of 14.62, thus achieving dual-resonance dynamic switching control in the terahertz band. The modulation depth of the switch at the two resonant frequencies is calculated using the following formula: ； in Relative modulation depth This represents the maximum transmittance of the device in the dielectric state. This represents the minimum transmittance of the device in its metallic state.

2. The actively modulated flexible dual-channel switchable terahertz modulator according to claim 1, characterized in that, For the polyimide dielectric layer, the thickness is 5 μm, and its relative permittivity is set to 3.5 + 0.0027i.

3. A design method for an actively modulated flexible dual-channel switchable terahertz modulator, implemented using the modulator described in claim 1, characterized in that, Includes the following steps: (1)Design the flexible substrate layer and the metasurface structure: The flexible substrate layer is made of polyimide material; the metasurface structure is composed of vanadium dioxide and metal materials, forming a vertical "I" - shaped periodic pattern, with a periodic size of 120 μm × 120 μm, and the minimum side length of the "I" - shaped periodic pattern unit is 10 μm; the thickness of the metasurface structure is 200 nm; (2) The external temperature is designed to be controlled from 20 ℃ to 87 ℃ to achieve the phase transition between the insulating and metallic states of vanadium dioxide; (3) The electromagnetic response characteristics of the flexible switchable dual-resonance terahertz filter metasurface structure were simulated and analyzed using electromagnetic full-wave simulation software. The boundary conditions in the x and y directions were set as periodic boundaries, while the z direction was set as an open boundary. By setting a plane wave port, the linearly polarized electromagnetic wave was made to propagate along the z-axis and be incident perpendicularly from the +z axis to the top layer region of the metasurface structure. The transmittance was monitored using an electric field probe. The simulation frequency range covered 0.1-2 THz, and the time-domain transmission line matrix method was used for calculation.

4. An application method for an actively modulated flexible dual-channel switchable terahertz modulator, implemented using the modulator described in claim 1, characterized in that, The dynamic switching device applied in the terahertz band combines the phase transition characteristics of vanadium dioxide with a dual-resonant metasurface design. It can achieve low-temperature full transparency and high-temperature dual-resonant switching functions in the 0.1-2 THz frequency band through temperature control. At low temperature, the emissivity is close to 0 dB; while at high temperature, it transforms into a metallic state and forms two resonance valleys through coupling with a metallic pattern, with resonant frequencies of 0.604 THz and 1.65 THz, respectively.

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