Reconfigurable chiral terahertz metasurface based on phase transition of vanadium dioxide

Abstract

This invention discloses a reconfigurable chiral terahertz metasurface design based on vanadium dioxide phase transition modulation. The device employs a metal-dielectric-metal structure, leveraging the order-of-magnitude abrupt change in conductivity during the phase transition from insulating to metallic states of vanadium dioxide to achieve dynamic reconfiguration of two operating modes. When vanadium dioxide is in the insulating state, the circular polarization conversion efficiency is above 0.9 in the 4.23–9.30 THz frequency range, with an operating bandwidth of 5.07 THz and a peak conversion efficiency exceeding 0.999, enabling wide-band circular polarization modulation. In the metallic state, the device achieves an absorption circular dichroism value of 0.93 at 7.06 THz, exhibiting a significant spin asymmetric response. This invention proposes an integrated scheme that achieves broadband polarization conversion and chiral absorption in a single device structure, providing a novel design approach and reference for device development in areas such as terahertz dynamic wavefront manipulation, polarization device development, and chiral sensing.

Description

Technical Field

[0001] This invention relates to the field of micro-nano integrated optoelectronics technology, specifically to a reconfigurable chiral terahertz metasurface design based on vanadium dioxide phase transition modulation. Background Technology

[0002] Terahertz waves (0.1–10 THz) lie between microwaves and the infrared spectrum, possessing physical properties such as transient response, wide bandwidth, low photon energy, and strong penetration. They are widely used in non-destructive testing, biomedical analysis, imaging, and wireless communication. However, the extremely weak THz response of natural materials has limited the development of high-performance devices.

[0003] Metasurfaces, as two-dimensional planar forms of metamaterials, are composed of periodically arranged subwavelength resonant units, allowing for precise control of the amplitude, phase, polarization, and propagation mode of electromagnetic waves within the interface layer. Vanadium dioxide (VO2) undergoes an insulator-metal phase transition near its critical temperature of approximately 68°C, resulting in an electrical conductivity spanning nearly five orders of magnitude between the two phases. Furthermore, it is compatible with thermal, electrical, and optical multimodal excitation and possesses a sub-nanosecond ultrafast response, making it an ideal material for constructing tunable metasurfaces.

[0004] Early research focused primarily on achieving single functions such as broadband polarization conversion or chiral selective absorption. As research progressed, scholars began exploring the possibility of realizing multifunctional reconfigurable functions within the same metasurface. In 2020, Song et al. simultaneously achieved broadband absorption and polarization conversion within the same frequency range on the same VO2 metasurface, advancing the design paradigm of dual-state coexistence in single devices. In 2023, Jin et al. theoretically revealed the strong circular dichroism of the insulating state and the broadband half-wave plate characteristics of the metallic state in VO2-based metamaterials, demonstrating cross-modal polarization control capabilities; Zhao et al. utilized the carrier temperature-sensitive properties of InSb to achieve broadband reflective linear polarization conversion from 1.21 to 1.92 THz. In 2026, Ma et al. proposed a five-layer cascaded VO2-metal composite metasurface, achieving ultra-wideband absorption in the metallic state and high-efficiency polarization conversion in the insulating state, with overlapping functional frequency bands, eliminating the defect of functional band separation. Despite significant progress in many areas of research, achieving broadband circular polarization conversion and strong circular dichroism absorption in a single structure in the terahertz band remains a major challenge. Summary of the Invention

[0005] Based on the above background, the present invention provides a design method and simulation data for a reconfigurable chiral terahertz metasurface based on vanadium dioxide phase transition modulation, which can realize broadband circular polarization conversion and strong circular dichroism absorption.

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

[0007] A reconfigurable chiral terahertz metasurface design based on vanadium dioxide phase transition modulation is presented. The metasurface unit structure has a continuous gold film (Au) as the substrate, a polyimide (PI) material as the intermediate layer, and a top layer composed of gold and vanadium dioxide. Through the two-phase switching of VO2, the same physical structure can achieve two completely independent functions, realizing dual-mode reconfigurable control of the device.

[0008] Compared with the prior art, the present invention has the following advantages:

[0009] (1) The present invention is based on a single material phase change mechanism, which not only avoids complex external control structures, but also significantly improves the integration and reliability of the device.

[0010] (2) In the VO2 insulating state, the device of the present invention achieves ultra-wideband circular polarization conversion in the frequency band of 4.23~9.30 THz, and the PCR is higher than 0.9 (with a peak value of 0.999) throughout the entire working frequency band, demonstrating excellent broadband polarization manipulation capability; after phase transition to the metallic state, a CD value of 0.93 is obtained at 7.06 THz, realizing chiral selective absorption.

[0011] (3) Based on the classic MIM architecture, this invention simplifies the device structure while ensuring high-performance output, and achieves a better balance between design simplicity, functional integration and core performance indicators, showing good application potential.

[0012] (4) This invention provides an effective path for synergistically realizing broadband polarization control and chiral absorption in a single metasurface structure, and has important reference significance in terahertz information modulation and multifunctional integrated device design. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the design and operating mode of a reconfigurable chiral terahertz metasurface structure based on vanadium dioxide phase transition regulation.

[0014] Figure 2 Reflectance curves of the invented structure under two circularly polarized incident conditions when vanadium dioxide is in the insulating state.

[0015] Figure 3 Polarization conversion rate spectral curves of the invented structure under two circularly polarized incident conditions when vanadium dioxide is in the insulating state.

[0016] Figure 4 The reflectance curve of the invented structure when it is in the metallic state of vanadium dioxide.

[0017] Figure 5 The absorption rate and circular dichroism curves of the invented structure when it is in the metallic state of vanadium dioxide. Detailed Implementation

[0018] To better understand the present invention, the following description and explanation are provided in conjunction with the embodiments and accompanying drawings. The embodiments described below are for illustrative purposes only and are not intended to limit the present invention.

[0019] like Figure 1 As shown in (a), a reconfigurable chiral terahertz metasurface based on vanadium dioxide phase transition modulation has a substrate of a continuous gold film with a thickness of H1 for reflecting terahertz waves; an intermediate layer made of polyimide with a thickness of H2; and a top layer composed of gold and vanadium dioxide, with two L-shaped structures asymmetrically arranged along the x and y axes, each with a thickness of H3. The period of the metasurface unit structure is P, and the lengths of the two gold arms are L1 and L2, and the widths are W1 and W4. Similarly, the lengths and widths of the vanadium dioxide arms are L3 and L4, W2 and W3.

[0020] like Figure 1 As shown in (b), when VO2 is in an insulating state (i.e., conductivity) When the polarization ratio is 20 S / m, the electromagnetic response of the device is mainly dominated by the coupling effect between the Au resonator arm and the MIM cavity mode, and the overall performance is characterized by efficient broadband circular polarization conversion.

[0021] like Figure 1 As shown in (c), when VO2 is excited to the metallic state, the conductivity is =2×10 5 The S / m and VO2 arms exhibit metallic conductivity, forming a composite chiral resonant structure together with the Au arm. This excites a strong spin-selective absorption effect, and the device switches to a high circular dichroism operating mode.

[0022] like Figure 2 As shown, in the ultra-wideband of 4~9THz, cross-polarized reflectivity dominates, while co-polarized reflectivity is suppressed, confirming that most of the energy of the incident circularly polarized light undergoes spin chirality reversal after reflection by the metasurface.

[0023] like Figure 3 As shown, the device's PCR efficiency is above 0.9 in the 4.23~9.3THz frequency band, with a working bandwidth of 5.07 THz and a peak efficiency of 0.999. Meanwhile, the absorption rate in this frequency band remains at a low level, indicating that the electromagnetic energy is mainly used for polarization state conversion with minimal loss, and the device has excellent polarization control performance.

[0024] like Figure 4 As shown, under RCP incident light, the total reflectivity in the mid-to-high frequency band remains at a low level, and most of the electromagnetic energy is absorbed by the device; while under LCP incident light, the total reflectivity is high, and energy is difficult to couple into the structure.

[0025] like Figure 5As shown, the absorption rate of the device is significantly higher when RCP is incident than when LCP is incident, and the absorption difference between the two reaches its maximum at 7.06 THz, corresponding to a CD peak of 0.93, which shows strong chiral selective absorption.

[0026] The above-described embodiments are merely illustrative of the present invention and are not intended to limit the scope of the present invention. Any equivalent modifications or improvements made by those skilled in the art to the technical solutions of the present invention without departing from the principles of the present invention shall be deemed to be within the protection scope of the present invention.

Claims

1. A reconfigurable chiral terahertz metasurface design based on vanadium dioxide phase transition modulation, characterized in that: The unit structure, from bottom to top, consists of a continuous gold reflective layer, a polyimide interlayer, and a gold-vanadium dioxide composite resonator. The period P of the metasurface unit structure is fixed at 16 μm; the thickness H1 of the bottom gold film is fixed at 0.3 μm; the thickness H2 of the polyimide interlayer is fixed at 6 μm; the height H3 of the top gold and vanadium dioxide layers is fixed at 0.3 μm; the lengths L1 and L2 of the two arms of the top gold arm are fixed at 9.1 μm and 12.3 μm, respectively; the arm widths W1 and W4 are fixed at 2.1 μm and 1.2 μm, respectively; and the arm lengths L3 and L4, and the arm widths W2 and W3 of the vanadium dioxide arms are fixed at 3.5 μm, 8.6 μm, 0.6 μm, and 0.6 μm, respectively.

2. The reconfigurable chiral terahertz metasurface based on vanadium dioxide phase transition control according to claim 1, characterized in that: The substrate in the structure is made of gold with a fixed height of 0.3 μm, and the period P of the unit structure is fixed at 16 μm.

3. The reconfigurable chiral terahertz metasurface based on vanadium dioxide phase transition control according to claim 1, characterized in that: The intermediate layer in the structure is made of polyimide material with a fixed height of 6 μm, and the period P of the unit structure is fixed at 16 μm.

4. The reconfigurable chiral terahertz metasurface based on vanadium dioxide phase transition control according to claim 1, characterized in that: The height of the top gold layer is fixed at 0.3 μm; the lengths of the gold arms are fixed at 9.1 μm and 12.3 μm, and the widths are fixed at 2.1 μm and 1.2 μm, respectively.

5. The reconfigurable chiral terahertz metasurface based on vanadium dioxide phase transition control according to claim 1, characterized in that: The height of the top vanadium dioxide layer is fixed at 0.3 μm; the lengths of the vanadium dioxide arms are fixed at 3.5 μm and 8.6 μm, and the widths are fixed at 0.6 μm and 0.6 μm, respectively.

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