Angularly Tunable Circular Dichroism in a Bilayer Plasmonic Metasurface via Interlayer Coupling

Abstract

We present a theoretical and computational study of a bilayer scythe-shaped metasurface designed to enhance chiroptical responses in the near-infrared region. The structure demonstrates pronounced differences in transmittance for left- and right-circularly polarized (LCP and RCP) light, directly related to the interlayer rotation angle. We show that circular dichroism (CD) increases with this rotation angle, reaching a maximum at 24°, indicating a significant enhancement of the chiral light–matter interaction at this specific geometry. Detailed analysis of the electric field distribution reveals distinct patterns for LCP and RCP light, providing insight into the underlying mechanism of the enhanced chiroptical response. Specifically, LCP light exhibits a stronger electric field intensity along the edges of the scythe meta-atoms compared to RCP light. Furthermore, the CD value increases as the interlayer distance decreases, highlighting the crucial role of interlayer coupling in enhancing the chiroptical performance. These results demonstrate that the chiroptical response of the bilayer and synthetic metasurface can be precisely controlled through its geometric parameters. This control enables the design of novel metasurfaces with potential applications in advanced nanophotonics, chiral sensing, and polarization control. The ability to tailor the chiroptical response by adjusting the metasurface configuration opens new avenues for developing compact and efficient optical devices.

Introduction

Chirality, the fundamental property of an object that lacks mirror symmetry, is pervasive across diverse scales from the molecular realm of DNA and amino acids to macroscopic structures such as galaxies. In optics, this handedness manifests as a differential interaction with left- and right-circularly polarized (LCP and RCP) light. − This leads to phenomena such as circular dichroism (CD), the differential absorption or extinction of LCP and RCP light, and optical rotation (OR), the rotation of the plane of polarization. ,,,, The ability to harness and enhance chiroptical effects is of paramount importance for a myriad of applications, including enantiomer discrimination, advanced polarization control, the engineering of materials with exotic optical properties, and optical sensing. −

Metasurfaces, two-dimensional arrays of subwavelength meta-atoms, have emerged as a transformative platform for manipulating light’s fundamental properties, including phase, amplitude, and polarization. − Precise design of meta-atom geometry and arrangement allows metasurfaces to achieve optical functionalities that surpass the limitations of conventional optical components. ,, Chiral metasurfaces, in particular, are engineered to exhibit strong chiroptical responses by breaking mirror symmetry either within the meta-atom itself or in its arrangement. ,− Compared to bulk chiral materials, metasurfaces offer significant advantages, including miniaturization, enhanced light–matter interactions due to their resonant nature, and unprecedented design flexibility. ,−

Chirality in metasurfaces can be realized through either intrinsic asymmetry, arising from the inherent three-dimensional or two-dimensional shape of the meta-atoms, or extrinsic asymmetry, resulting from the asymmetric arrangement of meta-atoms (which may themselves be achiral) with respect to the direction of incident light. ,,− A key challenge in the field is achieving strong chirality, quantified by high CD values, to enable practical applications. Researchers have explored various strategies to enhance chiroptical effects, including tailoring plasmonic resonances, utilizing low-loss dielectric materials, and employing complex three-dimensional or multilayer architectures. ,− Remarkably, the DNA double helix already serves as a model for strong chiral interactions. − The right-handed helical shape that provides DNA its intrinsic chirality is created by the stacked DNA base pairs with a continuous rotation of around 36° between each step. ,,,,−

Multilayer metasurfaces, where vertically stacked meta-atom layers interact through near-field coupling, provide a powerful approach to significantly boost chiroptical responses. − The interlayer interaction, controlled by parameters such as interlayer distance and relative rotation angle, can lead to hybridization of resonances and a substantial enhancement of CD compared to single-layer structures. ,,− This approach also enables precise control over the spectral position and magnitude of the chiroptical response. Specifically, the relative rotation between successive layers is a critical parameter that can dramatically influence the chiroptical properties. Transmission in molecular systems, such as DNA, refers to supercoiling effects and helical. Motion is determined by the strand’s twist angle rather than optical transmittance. In this setting, the ability to achieve a massive chiroptical response through simple geometric control is quite desirable.

Here, we present a design and computational study of a bilayer chiral metasurface based on scythe-shaped meta-atoms. We systematically investigate the influence of the relative rotation angle between the two layers on the metasurface’s chiroptical properties in the near-infrared (NIR) region, with a focus on transmission characteristics and CD. Through finite-element method (FEM) simulations, we demonstrate that the transmission difference between LCP and RCP light, and consequently the CD, increases with the rotation angle, reaching a maximum at 24°, and decreases as the interlayer distance is decreased. We further analyze the distinct electric field distributions for LCP and RCP light to elucidate the underlying mechanisms responsible for this enhanced chiroptical response. This study provides insights into the fundamental relationship between metasurface geometry and chiroptical response and establishes a design strategy for achieving enhanced chirality in nanophotonic devices.

Methodology

Simulation Setup

The optical properties and chiroptical responses of the bilayer Scythe chiral metasurface were examined using the FEM based on COMSOL Multiphysics software 6.1. A three-dimensional (3D) model was constructed to simulate the interaction between light and the metasurface. Figure a shows the schematic of the unit cell of the proposed bilayer scythe chiral metasurface, comprising two layers of gold (Au) scythe meta-atoms separated by a silicon dioxide (SiO2) spacer layer and situated on a SiO₂ substrate. The top Au scaffold meta-atom layer is rotated counterclockwise (CCW) with respect to the bottom layer by an angle α, introducing chirality into the structure. This advance is representative of a more general approach to chiral metasurface design, which involves determining the intended CD and then iteratively optimizing geometry using numerical simulations. The geometric parameters were defined as follows: the periodicity (P) of the unit cell in both the x and y directions was 500 nm, the outer radius (R) and inner radius (r) defining the scythe shape were 120 and 90 nm, respectively, the thickness (t) of the Au meta-atoms was 100 nm, the thickness (d) of the SiO₂ spacer layer was 50 nm, and the thickness of the SiO₂ substrate was 200 nm. The refractive index of the surrounding medium was set to 1 (air), the refractive index of the SiO₂ spacer and substrate was 1.45, and the optical properties of gold were described by the Drude model. Figure b shows the simulated copolarized transmittance spectra for LCP and RCP light in the reference configuration. The maximum LCP transmittance is about 0.82, and the minimum RCP transmittance is about 0.11. Both of these happen close to the resonance wavelength of λ = 1000 nm. This significant difference in transmission between the two polarization states, which is almost 0.71 in absolute transmittance, directly shows the strong chiroptical response of the structure and leads to the parametric optimization of α and d that will be discussed in the next sections.

1.

(a) Bilayer scythe-shaped chiral metasurface schematics, which have two Au meta-atom layers separated by a SiO₂ spacer layer on a SiO₂ substrate. The metasurface is illuminated by LCP and RCP circularly polarized plane waves that move along the negative z-axis. Geometric parameters: unit cell periodicity P = 500 nm, the outer radius R = 120 nm, inner radius r = 90 nm, meta-atom layer thickness t = 100 nm, interlayer SiO₂ spacer thickness d = 50 nm, and SiO₂ substrate thickness = 200 nm. The top layer is rotated counterclockwise by angle α relative to the bottom layer. Refractive indices: SiO₂ n = 1.45, and the surrounding medium (air) n = 1.0; Au is described by the Drude model. (b) Simulated copolarized transmittance spectra (normalized, 0–1) for LCP and RCP illumination at the reference configuration (α = 24°, d = 50 nm), showing a maximum LCP transmittance of ∼0.82 and a minimum RCP transmittance of ∼0.11 at the resonance wavelength λ = 1000 nm. This shows how well the chiral metasurface responds to different polarizations.

Boundary Conditions and Meshing

Periodic boundary conditions (PBCs) were applied along the x and y directions to simulate an infinite array of metasurface structures. Perfectly matched layers (PMLs) were implemented at the top and bottom boundaries along the z direction to absorb scattered light and prevent reflections, mimicking an open-boundary scenario. The mesh was generated using a physics-controlled mesh setting with the “Extremely fine” element size option to ensure accuracy, particularly around the scythe meta-atoms where field enhancement is expected. Convergence tests were undertaken to ensure that the numerical results were reliable in terms of mesh density. Beyond the conventional meshing and parameter sweeps, optimization approaches such as topology optimization and machine learning can significantly speed up the design process. Recent research has demonstrated that deep learning models (such as convolutional neural networks and generative adversarial networks) can predict ideal meta-atom shapes for target chiroptical responses. While not implemented here, these ideas are a significant future extension for getting stronger CD at a lower computational cost.

Excitation and Calculation

The metasurface was illuminated by a circularly polarized plane wave propagating along the negative z-axis. Two separate simulations were conducted: one for LCP light and one for RCP light incidence. The electric field components for LCP and RCP light were defined as E_LCP and E_RCP, respectively. The simulations were performed over a frequency range corresponding to the near-infrared spectrum. The CD was determined from the difference in transmittance between LCP and RCP light using the formula CD = $\frac{|T_{\mathrm{L}\mathrm{C}\mathrm{P}}-T_{\mathrm{R}\mathrm{C}\mathrm{P}}|}{|T_{\mathrm{L}\mathrm{C}\mathrm{P}}+T_{\mathrm{R}\mathrm{C}\mathrm{P}}|}|$ . The electric field distributions on the surface of the meta-atoms and in the surrounding region were also calculated to understand the underlying physical mechanisms of the chiroptical response.

Mathematical Formalism

The scythe structure of the meta-atoms is asymmetric and lacks rotational symmetry, which ensures that it responds differently to the LCP and RCP light. The transmission matrices from the linear to the circular polarization are given below

$$\mathbf{T}=\left[\begin{array}{ll}{t}_{++}& t_{+-}\\ t_{-+}& t_{--}\end{array}\right]=\frac{1}{2}\left[\begin{array}{ll}{t}_{xx}+t_{yy}+\mathrm{i}(t_{xy}-t_{yx})& t_{xx}-t_{yy}-\mathrm{i}(t_{xy}+t_{yx})\\ t_{xx}-t_{yy}+\mathrm{i}(t_{xy}+t_{yx})& t_{xx}+t_{yy}-\mathrm{i}(t_{xy}-t_{yx})\end{array}\right]=M^{-1}TM$$ 1

where t _xy is the transmission coefficient for x-polarized incident light to y-polarized transmitted light. M = $\frac{1}{\sqrt{2}}\left(\begin{array}{cc}1& 1\\ i& -i\end{array}\right)$ is the Cartesian to circular transformation matrix, and t _+– represents LCP incidence and RCP transmission.

Transformation is thus important to understand the chiral nature of the scythe chiral metasurface. Therefore, the conversion of linear to circular polarization captures the chiroptical characteristics in the scythe chiral metasurface. CD difference in absorption between the LCP and RCP light

$$\mathrm{C}\mathrm{D}=\frac{|T_{\mathrm{L}\mathrm{C}\mathrm{P}}-T_{\mathrm{R}\mathrm{C}\mathrm{P}}|}{|T_{\mathrm{L}\mathrm{C}\mathrm{P}}+T_{\mathrm{R}\mathrm{C}\mathrm{P}}|}|$$ 2

The transmittance values are given as absolute normalized transmittance (0:1), which is the ratio of the transmitted power flux to the incident power flux integrated over the exit port boundary.

Results

Transmission Spectra

The transmittance spectra in the scythe-shaped chiral metasurface are crucial because it indicates how they modify the incident light. Co-polarized transmittance refers to the light that has passed but preserves its polarization, whereas cross-polarized transmittance refers to the light that has changed polarization during transmission. This discrepancy is significant when studying chiral metasurfaces, which have chiral properties that change depending on the polarization of incident light. In this study, we used copolarized transmittance to scrutinize the chiroptical response of the metasurface.

The transmittance spectra of the scythe-shaped bilayer chiral metasurface were assessed in the NIR band for several rotation angles (22°, 23°, and 24°). The primary objective of this evaluation was to ascertain the impact of the geometric rotation on the optical characteristics of the scythe metasurface. The rotation angle between the two layers of the meta-atom is critical because it controls how the layers interact with each other, which influences the overall chiroptical response of the scythe-shaped chiral metasurface.

The transmittance values indicate the metasurface selectivity at certain wavelengths, as shown in (Figure b). Remarkably, it can be seen that the LCP and RCP light exhibited divergent transmittance values. This is evidenced by the peaks and troughs that align with the resonance modes for the 2 by 2 unit cell arrangement (Figure b). This asymmetry in the transmittance spectra shows that the metasurface has a pronounced chiroptical response, signifying that it transmits light depending on the incident light’s handedness. The transmittance value at a 24° rotation angle showed a unique response compared to the other rotation angles, signifying a substantial dependence of the scythe shape bilayer chiral metasurface on the rotation angle.

2.

Schematics of the 2 × 2 bilayer scythe-shaped unit cell array that shows LCP and RCP illumination. The rotation angle α and the thickness of the Au layer t are also shown. (b) Simulated copolarized transmittance spectra (absolute normalized transmittance, 0–1) for LCP (solid lines) and RCP (dotted lines) illumination at rotation angles α = 22°, 23°, and 24° (d = 50 nm, t = 100 nm). The LCP transmittance reaches a maximum of ∼ 0.82 near λ = 1000 nm, while the RCP transmittance reaches a minimum of ∼0.11 at the same wavelength, with the LCP–RCP separation increasing progressively with α, consistent with the enhanced CD reported in Figure .

Circular Dichroism

Description and Significance of CD

Circular dichroism measures how differently chiral structures absorb LCP and RCP light, playing a crucial role in elucidating the chiroptical response of the chiral metasurface. CD is more than measuring the optical properties of the metasurface; it also distinctly indicates the asymmetry in the metasurface’s interaction with polarized light, revealing the chiroptical aspects of the metasurface structure. Thus, examining CD is crucial for improving and comprehending the design and functionality of chiral metasurfaces in advanced photonics applications such as detection of enantiomer chirality in chemical analysis and enhancing the performance of photonic devices, where the precise control of light is vital.

CD Analysis

Figure illustrates that the CD value displayed significant peaks in the NIR region, attributed to the unique configuration of the bilayer scythe-shaped chiral metasurface (Figure a).

3.

Chiroptical response of the chiral metasurface as a function of the rotation angle. (a) Top view of the unit cell arrangement demonstrating the counterclockwise rotation angle α in between the top and bottom layers, defined relative to the dashed reference axis. (b) Maximum CD as a function of rotation angle α (5°–30°), extracted at λ = 1000 nm. The curve shows a well-defined peak at α = 24° (CD = 0.74), with monotonic rise and decline on either side. The peak CD value as a function of α and interlayer distance is summarized in Figure .

Figure b illustrates the examination of the CD value of the metasurface at various rotation angles, specifically the 5° to 30° counterclockwise (CCW) rotations of the top layer with respect to the bottom layer while maintaining the other parameters constant. The CD value progressively increased with the rotation angle, rising from approximately 0.5 at 5° to 0.72 at 23° and ultimately reaching its maximum of 0.74 at 24° (Figure b). To thoroughly delineate the dependence of CD on the rotation angle, we expanded the parametric sweep from α = 5° to α = 30°. The CD vs α curve (Figure a–c), taken at λ = 1000 nm, shows a clear and well-defined maximum at α = 24° (CD = 0.74). This is a 47% increase over the near-aligned configuration at α = 5° (CD = 0.50). The CD rises steadily from 5° to 24° and then falls steadily to 0.68 at α = 30°. This proves that the peak is a real maximum and not an artifact of limited sampling, Figure b. This value is associated with the interaction between the two layers and the positioning of the meta-atoms. ,

The maximum at α = 24° comes from the shape of the scythe itself. The blade tip of the top layer moves toward the arc body of the bottom layer as α goes up. At α ≈ 24°, the two layers are at their highest geometric overlap. In this setup, the blade tip makes a very localized near-field that connects asymmetrically with the arc body when lit by LCP and RCP. This is shown directly by the different hotspot distributions in Figure , where blade-tip enhancement is stronger under RCP and arc-end enhancement is stronger under LCP. When the blade tip goes beyond 24°, it moves past the arc body, which reduces the geometric overlap and weakens the asymmetric coupling. This is what causes the CD to go down. At the resonance frequency, the CD value exhibited a clear proportionality to the rotation angle. Hence, fine-tuning the geometric parameters offers an effective strategy to amplify the chiroptical response of the scythe-shaped chiral metasurface, resulting in an optimized higher CD value.

5.

Electric field norm distribution |E| (V/m) of the bilayer scythe-shaped chiral metasurface at the peak CD resonance wavelength λ = 1000 nm, (a) LCP and (b) RCP light, at the optimized rotation angle (α = 24°), d = 50 nm, t = 100 nm. Color scale: 0 to 1.0 V/m (identical for both panels), where 1.0 V/m equals the incident plane wave amplitude E ₀.

In contrast to symmetric structures, such as cylindrical or spherical chiral metasurfaces, the configuration of the scythe structure demonstrated an enhanced chiroptical response. C4 symmetric structures, such as cylindrical and gammadion meta-atoms, exhibited limited CD due to their symmetrical interactions. In contrast, the scythe-shaped chiral metasurface broke the rotational symmetry, resulting in an enhanced chiroptical response. The results indicate that the bilayer scythe-shaped chiral metasurface effectively enhances the chiroptical response, rendering it suitable for polarization control and biosensing applications.

Figure shows the CD response as a function of the two main geometric parameters that were measured at a peak resonance wavelength of λ = 1000 nm. Figure a shows the full rotation angle sweep from α = 5° to 30°. The CD steadily rises from 0.50 at α = 5°, where the layers are almost perfectly aligned, and geometric chirality is low, to a sharp, well-defined maximum of 0.74 at α ≈ 24°, which is a 47% increase. After the peak, the CD steadily drops to 0.68 at α = 30°, which shows that the peak is real and that there is no higher CD at larger angles. (Figure b) The distance between layers changes from d = 50 to 150 nm at the best angle (α = 24°). The CD drops linearly from 0.74 at d = 50 nm to 0.70, 0.65, and 0.60 at 75, 100, and 125 nm, respectively, and finally to 0.55 at d = 150 nm. This is a 26% decrease over the range that was sampled. This steady decay is a direct result of the fact that near-field coupling between the two Au layers is only temporary. As d gets bigger, the field overlap gets weaker, which lowers the LCP/RCP coupling asymmetry that causes the chiroptical response.

4.

Parametric dependence of peak CD on geometric parameters, evaluated at λ = 1000 nm. (a) CD as a function of the interlayer rotation angle α (5°–30°) at fixed d = 50 nm, showing a well-defined maximum of CD = 0.74 at α ≈ 24° with a confirmed decline to 0.68 at α = 30°. (b) CD as a function of interlayer distance d (50–150 nm) at fixed α = 24°, showing a monotonic decrease from 0.74 at d = 50 nm to 0.55 at d = 150 nm.

As summarized in Figure , the CD reaches a maximum of 0.74 at α = 24° and decreases monotonically with increasing interlayer distance, with both trends evaluated at λ = 1000 nm.

Electric Field Distribution

The assessment of the electric field distribution elucidated the mechanism underlying the enhanced chiroptical response in the scythe-shaped chiral metasurface. The electric field distribution at various rotation degrees matched the intensity variation in the field coupling between the meta-atom layers induced by alterations in the rotation angle. This study examined the role of interlayer rotation angles in enhancing field coupling to optimize the chiroptical response in the metasurface, building upon prior investigations of geometrical parameters such as shape, interlayer spacing, and orientation. By assessing the field distribution at various rotation angles between the layers, we interpreted the effect of geometric parameters on identifying the optimal design and CD. The field distribution for the LCP and RCP light at the maximum chiroptical response showed the critical areas of field enhancement and localization, as shown in Figure .

This field localization that depends on polarization is quite similar to the intrinsic chiroptical behavior of the strand illuminated by the LCP and RCP conditions, with one polarization coupling more effectively to the helical structure than the other. These changes are evident as quantifiable CD, driven by selective near-field enhancements. The scythe-shaped chiral metasurface reproduces the principle on a nanophotonic platform, wherein the designed shape dictates asymmetric hot-spot localization akin to the chiral field concentrations found in biomolecular helices.

At the maximum chirality, the field distribution for the RCP light exhibited a significant concentration of the electric field at the tips and edges of the scaffold structure, as illustrated in Figure . The plasmonic resonance in these areas was notably significant, leading to enhanced interactions with the incident CPL. The scythe-shaped bilayer structure of the metasurface prompted the electric field to localize uniquely for the LCP and RCP light, as shown in Figure . Under ideal chiroptical response conditions (α = 24, t = 100 nm, and d = 50 nm), the scythe-shaped chiral metasurface exhibited significantly enhanced and more localized field intensities. This was pronounced in the edges of the scythe shapes, where the field concentration was high. The enhanced localization of fields in the meta-atoms enabled more robust interactions with the incident circular polarized light, hence augmenting chirality. These findings indicate that the scythe-shaped chiral metasurface enhanced the overall field distribution and optimized the electromagnetic interactions necessary for effective chiroptical applications. The enhanced electric field distribution is essential for attaining heightened sensitivity and performance in practical devices utilizing chiral metasurfaces. As the rotation angle changed from 22° to 24°, the localization of the electric field at the scythe edge increased, resulting in heightened electric field concentration in areas that amplified the chiroptical response.

The chiroptical response exhibited an increase as the rotation angle progressed from 22° to 24°, resulting in a more pronounced difference between the electric field of the left circularly polarized light (ELCP) and right circularly polarized light (ERCP) throughout the meta-atom structure. At reduced rotation angles, the overlap of the fields between layers diminished, resulting in weak plasmonic coupling and lower chiroptical response. The increased rotation angle of 24° resulted in the bilayer scythe-shaped chiral metasurface enhancing near-field coupling, which in turn led to intense electric field localization and significantly improved CD.

Discussion

This study investigated the chiroptical properties of a scythe-shaped chiral metasurface using theoretical and computational methods. The results demonstrate that the optical response, particularly the transmission characteristics and CD, is strongly dependent on the geometric parameters, specifically the relative rotation angle between the layers and the interlayer distance, as illustrated in Figures and b, respectively.

The significant finding is the difference in transmission between LCP and RCP light, which accounts for the observed CD. The differential interaction with LCP and RCP light was adjustable through the rotation angle. Simulations indicated that an increase in the rotation angle correlates with a progressive rise in the CD value, achieving a maximum exceeding 0.74 at a rotation angle of 24°. The CD response may diminish beyond this optimal angle, although this study concentrated on the peak. The significant CD value, exceeding 0.74 at a 24° rotation angle, underscores the potential of this structure for applications necessitating robust chiroptical effects, including advanced biosensing platforms, polarization-sensitive detectors, and optical filtering where selective interaction with CPL is essential. − ,− Our scythe-shaped chiral metasurface achieves maximum CD at approximately 24° rather than 36°. This analogy is conceptually important as both systems illustrate that chiral strength arises from discrete angular rotation among stacked layers.

The analysis of the electric field distribution demonstrated distinct patterns for the LCP and RCP incident light. The results demonstrated a more pronounced enhancement and distinct localization to the electric field along the edges of the she-scythe-shaped structure for one polarization relative to the other, especially at resonance. The difference in the electric field distribution for LCP and RCP light is directly linked to differential transmission and the pronounced chiral response, thereby validating that structural chirality results in a notable chiroptical effect at the nanoscale. The scythe chiral metasurface emulated this natural behavior in an engineered format: one handedness yields enhanced near-field localization and coupling compared with the other. This parallel reinforces the assertion that bioinspired angular stacking serves as an effective design principle for nanophotonic chirality.

The scythe-shaped bilayer chiral metasurface design is compatible with both bottom-up and top-down approaches. For bottom-up approaches, DNA origami scaffolding offers precise positional control for assembling chiral plasmonic configurations with defined twist angles, directly analogous to the interlayer rotation mechanism studied here. ,, Block copolymer directed self-assembly provides an additional scalable route for large-area bilayer patterning. For top-down fabrication, the structure can be realized via two aligned electron-beam lithography (EBL) steps with Au deposition and lift-off, separated by PECVD SiO₂ spacer deposition. , The 500 nm periodicity and 120 nm feature sizes are well within the standard EBL capability. While the present metasurface operates at λ = 1000 nm, visible range operation is achievable by scaling the geometric parameters by a factor of 0.55 to 0.65×, scaling down the periodicity to P ≈ 275–325 nm and the outer radius to 66–78 nm. Replacing Au with Ag or Al would further improve resonance quality by cutting down on the interband. ,, Looking ahead, combining the bilayer metasurface with cholesteric liquid crystals could lead to actively tunable chiroptical devices. The electrically switchable helical pitch of the liquid crystal layer could change the CD response of the plasmonic structure in real time, which would open up new possibilities for reconfigurable chiral photonics and optical sensing applications. −

The findings demonstrate the efficacy of the bilayer scythe-shaped chiral metasurface design in producing a robust and adjustable chiroptical response. The capacity to regulate CD through the adjustment of the rotation angle, along with the pronounced variation in interaction with LCP and RCP light, evident in both transmission and electric field distribution, renders this metasurface design advantageous for the advancement of sophisticated photonic devices with customized light–matter interactions. The insight enhances the comprehension of chiral phenomena in chiral metasurfaces and facilitates potential applications in asymmetric catalysis, enantiomer sensing, and polarization optics.

Conclusion

This study investigated the chiroptical properties of a bilayer scythe-shaped chiral metasurface, focusing on the analysis of CD and electric field distributions across various parameters, including interlayer distance and rotation angles in the NIR region. Our findings demonstrated that the optimized bilayer scythe-shaped chiral metasurface yields a significant chiroptical response. It is demonstrated that these chiral metasurfaces exhibit significant CD, which is dependent on the geometric parameters. The findings indicate that the maximum CD was achieved at a rotation angle of 24°, an interlayer distance of 50 nm, and a meta-atom thickness of 100 nm, highlighting the ability to precisely adjust the chiroptical response through modifications in the geometric parameters of the chiral metasurface. A comprehensive angular sweep from α = 5° to 30° confirms that a maximum CD of 0.74 is achieved at α = 24°, with a monotonic increase up to the peak and a confirmed decline beyond it, establishing the optimality of this rotation angle for the scythe bilayer geometry. The electric field distribution enhancement difference between the LCP and RCP light of the scythe metasurface has been distinctly observed and calculated. The selective enhancement is particularly evident for the LCP, as the electric field intensity rises with rotational modifications, underscoring the significance of geometric parameters in optimizing the chiroptical response.

This study contributes to a deeper understanding of the chiroptical response and its application in modern optical devices. Our research demonstrates the capacity to enhance and regulate specific optical properties, facilitating the advancement of advanced optical devices for applications in optical filtering, sensing, and telecommunications. Future research should concentrate on the integration of these chiral metasurfaces with other photonic systems and examine the effects of varying material compositions on the observed phenomena.

S.A. designed the metasurface, performed the numerical simulation, analyzed the chiroptical phenomena, and wrote the manuscript; B.K. contributed to manuscript proofreading. D.L. supervised the project, gave conceptual guidance, and verified the theoretical explanations of this work. All authors discussed the final results and contributed to the final manuscript.

The authors declare no competing financial interest.