A chiral metasurface design based on vanadium dioxide insulator-metal phase transition

Abstract

This invention discloses a chiral metasurface design based on the vanadium dioxide insulator-metal phase transition. The metasurface adopts a metal-insulator-metal configuration. When vanadium dioxide is in the metallic state, under circularly polarized light incidence, the metasurface exhibits a highly broadband circular dichroism response, achieving an extreme value of 0.95 at 4.98 THz and maintaining a stable value above 0.90 in a wide frequency range of 4.51–7.70 THz. Accompanying this strong chiral response, the structure also possesses a significant linear dichroism of 0.83. Most importantly, by thermally triggering the vanadium dioxide phase transition process, effective amplitude modulation and reliable switching control of this strong dichroism response can be achieved. This invention achieves reliable active control of the structural chirality, providing a practical approach for developing high-performance terahertz chiral photonic devices.

Description

Technical Field

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

[0002] Metasurfaces are two-dimensional periodic arrays composed of subwavelength micro- and nanostructures. By precisely controlling geometric and material parameters, key parameters such as the amplitude and phase of electromagnetic waves can be effectively manipulated. Metasurfaces based on chiral structures exhibit significantly different absorption, transmission, or scattering characteristics for left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP), thus producing the circular dichroism (CD) effect.

[0003] In the interaction between electromagnetic waves and chiral micro / nano structures, this selective response often manifests as other polarization-dependent effects such as linear dichroism. The physical basis for this lies in the unique electromagnetic coupling mechanism between chiral structures and electromagnetic waves of different polarization states, such as the relative phase and amplitude differences between electric and magnetic dipole moments.

[0004] Early research primarily focused on achieving single functions such as efficient circular dichroism (CD) or linear dichroism (LD). As research progressed, researchers began exploring the possibility of synergistically achieving multiple polarization modulation functions within the same metasurface. In 2022, Jiang et al. achieved a wide range of circular dichroism switching using GST phase-change materials. In 2024, Yang et al. achieved strong circular dichroism absorption based on graphene; Chen et al., through the synergistic effect of vanadium dioxide and graphene, achieved linear dichroism and tunable circular dichroism in the same device. In 2025, Liu et al. designed an omnidirectional bifunctional terahertz metasurface based on a multilayer composite structure, significantly expanding the terahertz wavefront modulation dimension while achieving efficient circularly polarized wave vortex generation and linearly polarized wave conversion. Despite significant progress in many aspects, achieving a single structure with wide-bandwidth, strong CD, and high LD synergistic response in the terahertz band, and possessing a wide range of continuous tuning capabilities, remains a significant challenge. Summary of the Invention

[0005] Based on the above background, the present invention provides a design method and simulation data for a chiral metasurface based on vanadium dioxide (VO2) insulator-metal phase transition, which can realize the enhancement and control of dichroism.

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

[0007] Based on a chiral metasurface design using a vanadium dioxide insulator-metal phase transition, this metasurface unit structure features a continuous gold film (Au) as the substrate, a polytetrafluoroethylene (PTFE) dielectric layer, and a top layer composed of gold and vanadium dioxide with varying heights. By thermally triggering the VO2 phase transition process, effective amplitude modulation and reliable switching control of a strong dichroic response can be achieved.

[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) Under circularly polarized light incidence, the present invention achieves a circular dichroism extremum of 0.95 at 4.98 THz and maintains a stable value above 0.90 in a wide frequency range of 3.2 THz. Accompanying this strong chiral response, the structure also exhibits a significant linear dichroism of 0.83.

[0011] (3) This invention almost completely suppresses left-handed circularly polarized light at 4.98 THz and significantly enhances circular dichroism. This achievement provides effective support for chiral optical information processing, biomedical detection and treatment, the development of novel chiral materials and devices, and stealth technology in the field of national defense and security.

[0012] (4) This invention provides an innovative design idea for developing high-performance, tunable terahertz chiral photonic devices, and is expected to promote the practical application of terahertz polarization modulation technology in imaging, communication and other fields. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a chiral metasurface design structure based on the vanadium dioxide insulator-metal phase transition.

[0014] Figure 2 The diagram shows the absorption rate and circular dichroism of the invented structure when circularly polarized light is incident.

[0015] Figure 3 The diagram shows the absorption rate and linear dichroism of the invented structure when linearly polarized light is incident.

[0016] Figure 4 The graph shows the effect of different electrical conductivities of vanadium dioxide on the circular dichroism of the invented structure.

[0017] Figure 5 The graph shows the effect of different electrical conductivities of vanadium dioxide on the linear dichroism of the invented structure. Detailed Implementation

[0018] To better understand the present invention, the present invention will be further explained and described below with reference to the embodiments and accompanying drawings. The following embodiments are only for illustrative purposes and are not intended to limit the present invention.

[0019] like Figure 1 As shown in (a), a chiral metasurface design based on vanadium dioxide insulator-metal phase transition consists of a continuous gold film reflective layer, a polytetrafluoroethylene dielectric layer, and a gold-vanadium dioxide composite resonator, arranged from bottom to top.

[0020] like Figure 1 As shown in (b), the thickness h of the underlying gold film Au The thickness of the polytetrafluoroethylene dielectric layer is h2, designated as "h1-h2". The gold and vanadium dioxide layers on the top layer have different heights, designated as h4 and h3 respectively.

[0021] like Figure 1 As shown in (c), P represents the period of the metasurface unit structure, the lengths of the metal arms of the cross structure are L1 and L2, and the width is w3. The inner radius of the gold open ring is R, and the ring width is w2.

[0022] like Figure 2 As shown, at a frequency of 4.98 THz, the absorptivity of RCP light is as high as 0.976, while that of LCP light is only about 0.026. Meanwhile, in a wide frequency range from 4.51 to 7.70 THz, the CD value is greater than 0.9, reaching a maximum of 0.95 at 4.98 THz.

[0023] like Figure 3 As shown, the LD reaches a peak value of 0.83 at 3.22 THz, where the absorptivity of x-polarized light is much higher than that of y-polarized light. This chiral structure exhibits significant polarization modulation capability for incident light with different linear polarization states. Its mechanism stems from the asymmetric coupling effect of the metasurface unit structure on different electric field components of linearly polarized light, i.e., the selective enhancement or suppression of electric field components in specific polarization directions.

[0024] like Figure 4 As shown, when VO2 is in a metallic state (e.g., 2×10⁻⁶), 5 At a conductivity of 100 S / m, the metasurface exhibits strong circular dichroism, with a CD value of 0.95 at 4.98 THz, and CD values ​​exceeding 0.9 across a wide bandwidth of 4.51–7.70 THz. Conversely, the CD value gradually decreases with decreasing conductivity, dropping to near zero in the insulating state with a conductivity of 100 S / m. This confirms that effective amplitude modulation and reliable active switching control of the circular dichroism response can be achieved by altering the conductivity of VO2 (i.e., triggering its phase transition between the insulating and metallic states).

[0025] like Figure 5As shown, the conductivity of VO2 also dominates the distribution characteristics of LD when x / y polarized light is incident. When the conductivity is 2 × 10⁻⁶... 5 At S / m, the maximum LD value can reach 0.83, and overall, the LD value decreases as the conductivity decreases.

[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 chiral metasurface design based on vanadium dioxide insulator-metal phase transition, characterized in that: The unit structure, from bottom to top, consists of a continuous gold reflective layer, a polytetrafluoroethylene (PTFE) dielectric layer, and a gold-vanadium dioxide composite resonator. The period P of the metasurface unit structure is fixed at 16 μm; the thickness "h1-h2" of the bottom gold film is fixed at 0.4 μm; the thickness h2 of the PTFE dielectric layer is fixed at 6 μm; the height h4 of the top gold layer is fixed at 1 μm; the height h3 of the top vanadium dioxide open ring is fixed at 0.5 μm; the lengths L1 and L2 of the metal arms of the cross-shaped structure are fixed at 8 μm and 6 μm, respectively; the width w3 is fixed at 0.8 μm; the inner radius R of the gold open ring is fixed at 6 μm; the ring width w2 is fixed at 1.5 μm; the ring parameter w1 is fixed at 1.9 μm; and the opening ring angle parameters α and β are fixed at 100° and 95°, respectively.

2. The chiral metasurface design based on vanadium dioxide insulator-metal phase transition according to claim 1, characterized in that: The substrate in the structure is made of gold with a fixed height of 0.4 μm, and the period P of the unit structure is fixed at 16 μm.

3. The chiral metasurface design based on vanadium dioxide insulator-metal phase transition according to claim 1, characterized in that: The dielectric layer in the structure is made of polytetrafluoroethylene with a fixed height of 6 μm, and the period P of the unit structure is fixed at 16 μm.

4. The chiral metasurface design based on vanadium dioxide insulator-metal phase transition according to claim 1, characterized in that: The height of the top gold layer is fixed at 1 μm; the lengths of the metal arms of the cross structure are fixed at 8 μm and 6 μm, and the width is fixed at 0.8 μm; the inner radius of the gold open ring is fixed at 6 μm; the ring width is fixed at 1.5 μm; and the angle parameters of the open ring are fixed at 100° and 95°.

5. The chiral metasurface design based on vanadium dioxide insulator-metal phase transition according to claim 1, characterized in that: The height of the top vanadium dioxide open ring is fixed at 0.5 μm, and the ring width is fixed at 0.4 μm.

Images