Search Results (74)

Strong chiral responses in planar dielectric metasurfaces are important for polarization-selective nanophotonic devices, but achieving large and reversible circular dichroism (CD) in simple dielectric structures remains challenging. This work proposes a symmetry-broken silicon metasurface that realizes near-infrared chiral response based on bound states in the continuum (BICs). The unit cell consists of a silicon nanoblock with two through-air grooves. The in-plane displacement of the air grooves breaks the C₂ rotational symmetry and splits the BIC-related polarization singularity into two circularly polarized points (C points) with opposite handedness. By further introducing out-of-plane tilting, one of the C points is shifted to the Г point, enabling spin-selective coupling between normally incident circularly polarized light and the quasi-BIC mode. Reversing the out-of-plane tilt switches the sign of CD, with values reaching −0.98 and 0.98, approaching the theoretical limits of ±1. Under oblique incidence, the structure can also exhibit near-limit CD responses. Finally, by introducing graphene, the structure achieves tunable circular-polarization-selective absorption, with the absorption of CD approaching the theoretical limits of ±0.5 for the coupled system. This work provides a new design idea for compact chiral nanophotonic materials by using symmetry breaking to control spin-selective quasi-BIC coupling and tunable chiral absorption. Full article

The interaction between light and chiral plasmonic metasurfaces provides a powerful mechanism for controlling polarization states at the nanoscale. Utilizing displacement Talbot lithography for large-area fabrication, we characterized the chiroptical response by measuring the evolution of Stokes parameters to quantify phase retardation between orthogonal polarization components. To elucidate the underlying physical mechanism, we employ a hybrid finite element method and rigorous coupled-wave analysis approach to investigate the behavior of the far-field and local-field configurations. Our results reveal that the phase shift is highly sensitive to symmetry-breaking features, where the interplay between different modes dictates the overall circular dichroism signal. Furthermore, the analysis of local field plots suggests specific contributions of plasmonic modes to the chiroptical response. We conclude that the phase shift effects, characterized via Stokes parameters and modal analysis, provide a robust metric for engineering chiroptical properties in these systems. This work establishes a fundamental framework for developing compact polarization-control elements and enhances the understanding of phase-modulated light-matter interactions in chiral plasmonic metasurfaces. Full article

We present a strategy for achieving precisely controllable circular dichroism (CD) in all-dielectric silicon metasurfaces by exploiting bound states in the continuum (BICs). By employing two topologically protected BIC modes and converting them into circularly polarized eigenstates through oblique illumination, we realize a reversal of maximum chirality without any modification to the metasurface geometry. The resulting CD exhibits opposite signs in two distinct spectral regions and can be flexibly adjusted through engineered structural perturbations. The associated quasi-BIC resonances deliver near-unity CD values (±1), ensuring highly efficient spin-selective transmission. Moreover, this platform enables substantial enhancement of multi-band chiral nonlinear optical responses, where the nonlinear emission becomes strongly dependent on the incident spin state across different frequency bands. Based on effective nonlinear efficiency, a sensitive refractive index sensor can be designed. This work offers a versatile route for tailoring extrinsic chirality in achiral metasurfaces and provides a promising foundation for multifunctional chiral photonic devices in applications such as biosensing, chemical detection, and advanced nonlinear optics. Full article

Conventional chiral metasurfaces are typically restricted to a single resonant wavelength, which limits their ability to satisfy the requirements of broadband detection and multi-channel polarization manipulation. To overcome this limitation, this study numerically proposes a chiral metasurface based on an oracle-bone-inspired geometry. By combining dislocation with rotational symmetry breaking, the proposed structure enables pronounced circular dichroism responses at three wavelengths in the long-wave infrared region, reaching 0.68@λ₁ = 10.43 μm, 0.79@λ₂ = 10.8 μm, and 0.6@λ₃ = 10.9 μm. This design overcomes the single-wavelength limitation of conventional chiral metasurfaces and establishes a new paradigm for multi-wavelength chiral light-field manipulation. This research not only broadens the design scope of chiral photonics, but also provides a promising technical path for the development of highly integrated infrared polarization devices and multi-wavelength chiral sensing systems. Full article

Multi-band circular dichroism (CD) with spectral tunability is highly desirable for chiral metasurface-based sensing and polarization control. In this work, we propose a mid-infrared (MIR) metal–insulator–metal (MIM) chiral metasurface absorber composed of gold-alumina-gold (Au-Al₂O₃-Au) layers, where chirality is introduced by symmetry breaking between two gold elliptical bars in the top layer. Finite element calculations show that the structure operates over 3.5–6.5 µm and produces dual-band CD responses with values of 0.83 and −0.81. The CD magnitude in each band can be independently tuned by adjusting the semi-major or semi-minor axis of the elliptical bars. In addition, rectangular slots inserted into the bars enable continuous redshift of the resonance wavelengths, and the tunability can be further enhanced by optimizing the slot dimensions. These results provide a practical strategy for designing tunable dual-band chiral absorbers and may be useful for future chiral sensing and polarization imaging applications. Full article

Extrinsic chiral metasurfaces offer a promising route for controlling chiroptical responses through incident angle variation, yet the simultaneous realization of strong circular dichroism and full-space polarization beam splitting remains challenging. In this work, we propose an all-dielectric extrinsic chiral metasurface that leverages obliquely incident terahertz waves to break in-plane symmetry, thereby activating out-of-plane multipoles and inducing strong spin-selective scattering. At an incident angle of 30°, the metasurface achieves efficient full-space separation of left- and right-handed circularly polarized waves, with a circular dichroism peak exceeding 0.7 near 0.48 THz. Moreover, by varying the incident angle or operating frequency, the polarization state of the reflected wave can be continuously tuned from linear to elliptical to nearly circular, as visualized on the Poincaré sphere. This angle-dependent, full-space polarization manipulation capability highlights the potential of the proposed metasurface for applications in advanced terahertz imaging, LiDAR, and integrated photonic systems. Full article

Circular dichroism is at the core of chiral spectroscopy and polarization light manipulation. However, achieving metal-based devices with high efficiency, compactness, and easy integration in the near-infrared band remains a significant challenge. Traditional metal chiral microstructures, such as broken open rings, helical lines, or waveplates–polarizers I confirm., are limited to circular dichroism values below 50% due to their inherent ohmic losses, severely restricting practical applications. To overcome this bottleneck, this paper proposes a twisted double-layer plasmonic metasurface composed of two anisotropic metal metasurfaces. This design breaks the mirror symmetry of the structure by precisely controlling the in-plane twist angle between the layers, inducing strong coupling and interference effects in the chiral optical response. Simulation results show that this device achieves excellent multi-wavelength circular dichroism control. At a wavelength of 1660 nm, the circular dichroism value reaches 0.48, and it further increases to 0.84 at 2200 nm, significantly surpassing the performance limits of traditional metal structures. This work not only provides a simple and scalable design paradigm for high-performance chiral optical devices but also opens up new avenues for advanced applications such as chiral molecular sensing, polarization coding, and quantum optics in the near-infrared band. Full article

The on-chip detection of circularly polarized light is pivotal for advancing applications in quantum optics, information processing, and spectroscopic sensing. However, conventional chiral metasurfaces often suffer from complex multilayer fabrication, material incompatibility, or modest performance, hindering their integration with photonic circuits. Here, we introduce a monolithic all-silicon metasurface that overcomes these limitations through a singular structural innovation. By strategically truncating four corners of a conventional Z-shaped meta-atom, we induce a hybridization of optical modes that profoundly enhances chiral light–matter interaction. This deliberately engineered perturbation yields a colossal circular dichroism with an extinction ratio exceeding 66 dB, a performance that surpasses existing state-of-the-art designs by approximately three orders of magnitude. Furthermore, the proposed metasurface exhibits remarkable fabrication robustness, owing to its single-layer architecture and CMOS-compatible material. We demonstrate that this exceptional metasurface can be directly integrated with a Mercury Cadmium Telluride (MCT) photodetector to form a highly efficient, compact circular polarization detector. Our work provides a simple yet powerful paradigm for creating high-performance chiral photonic devices, paving the way for their widespread adoption in integrated optoelectronics. Full article

The manipulation of vector beams (VBs) with longitudinally variant polarization states is an important research topic and has potential applications in classical and quantum fields. In this study, we propose a half-wave plate dielectric metasurface composed of two interleaved sub-metasurfaces to generate longitudinally separated dual-channel vectorial structured light fields. The propagation and Pancharatnam–Berry phases are employed to construct hyperbolic, helical, and opposite gradient phases for focusing wavefronts, generating circularly polarized (CP) vortices, and deflecting CP vortices with the same chirality in opposite directions. Consequently, dual-channel higher-order or hybrid-order Poincaré (HOP or HyOP) beams are generated along the optical axis under elliptically polarized illumination, and their polarization states evolve along an arbitrary pair of antipodal meridians on the HOP or HyOP sphere by varying the ellipticity of the incident light, the propagation-phase topological charge, and the rotation order of the meta-atom. The consistency between the theoretical and simulated results demonstrates the feasibility and practicability of the proposed method. This study is significant for compact, integrated, and multifunctional optical devices, and provides an innovative strategy to extend optical field manipulation from two-dimensional to three-dimensional space. Full article

Chiral bound states in the continuum (BIC) metasurfaces have emerged as a promising platform for enhancing light–matter interactions, which have potential applications in advanced photonic and quantum information devices. However, simultaneously achieving near-perfect circular dichroism and highly efficient nonlinear conversion with highly symmetric structures in metasurfaces remains an open challenge. In this work, we design a $C_4$-symmetric chiral metasurface composed of eight elliptical silicon nanorods on a ${\mathrm{SiO}}_2$ substrate, where monocrystalline silicon is used as the nonlinear optical material. By combining simulations and nonlinear time-domain coupled-mode theory (TCMT), we discovered that both the optimal chirality and the nonlinear conversion efficiency can be attained simultaneously due to the critical coupling between the metasurface mode and the quasi-BIC mode. Meanwhile, a near-perfect circular dichroism (CD = 0.99) and a high nonlinear conversion efficiency of $7\times {10}^{-5}$ under a radiation intensity of $5{\mathrm{kW}/\mathrm{cm}}^2$ are numerically achieved due to the robustness of bound states in the continuum. This work offers a promising route toward high-performance chiral nonlinear photonic components, which is of great importance for the development of ultra-compact optical devices such as circular polarization detectors, chiral sensors, and nonlinear photonic chips for integrated optical and quantum information systems. Our research not only contributes to the fundamental understanding of chiral metasurfaces but also provides a practical approach for achieving high-efficiency nonlinear optical devices. Full article

Mechanical properties of lead-free hybrid perovskites have attracted growing interest because of their significance in future eco-friendly optoelectronic applications. However, there are very limited studies about the intrinsic elastic properties and high-pressure structural evolution of hybrid perovskites, and the fundamental structure–mechanical property relationships are insufficiently understood. Here, we report the elastic behavior of a three-dimensional (3D) hybrid organic–inorganic perovskite, (DABCO)RbBr₃ (DABCO = triethylenediammonium), and confirm the processability through processing with chiral metasurfaces and the generation of circular dichroism. Our in situ high-pressure synchrotron X-ray diffraction experiments demonstrate that this crystal does not start to amorphize until 2.3 GPa. Density functional theory calculations reveal that its E, G and v range between 20.73 and 27.93 GPa, 8.21 and 11.62 GPa and 0.18–0.39, respectively. Additionally, due to the low elastic moduli and polar crystal structure, we fabricate a device of (DABCO)RbBr₃ composite film, which shows favorable performance for piezoelectric energy harvesting. This work utilizes (DABCO)RbBr₃ to open up new avenues for applications in manufacturing and energy harvesting. Full article

Chiral metasurfaces exhibit enormous potential in optical applications, and their integration with phase-change material vanadium dioxide (VO₂) provides a novel pathway for dynamic regulation. In this study, a chiral absorptive metasurface based on VO₂ is designed. By tuning the VO₂ conductivity around the operating frequency of 2.81 THz, the circular dichroism (CD) can be continuously adjusted from 0.06 to 0.95, realizing a high-contrast chiral switch. On this basis, the Pancharatnam–Berry (PB) phase is introduced to construct a chirality-dependent phase gradient: when the VO₂ conductivity is 200,000 S/m, only the left-handed circularly polarized (LCP) wave is subjected to periodic phase modulation, enabling controllable deflection of the reflected beam, while the right-handed circularly polarized (RCP) wave is selectively absorbed. This “chiral phase encoding” strategy simultaneously achieves absorptive CD tuning and reflective beam shaping on a single metasurface, significantly enhancing the flexible manipulation capability of circular polarization states in the terahertz band. It provides a compact and efficient solution for reconfigurable imaging, unidirectional communication, and integrated photonics systems. Full article

Although the polarization state, as a key physical dimension of light, plays an irreplaceable role in many frontier fields such as quantum communication and chiral sensing, traditional photodetectors are limited by the inherent optical isotropy of materials and thus are unable to directly distinguish circular polarization information. This paper numerically reports a miniature circular polarization photodetector based on chiral metasurfaces, which achieves an excellent extinction ratio of up to 31 dB through the collaborative regulation of geometric displacement manipulation and tilt angle operation. This device utilizes the symmetry-breaking effect to construct significantly different transmission spectral responses between left circularly polarized light (LCP) and right circularly polarized light (RCP). Our research not only provides a high-performance implementation solution for on-chip polarization detection but also opens up new paths for the future development of quantum optics, integrated sensing, and ultra-compact polarization optical systems. Full article

Vertical cavity surface emitting lasers (VCSELs) have shown great potential in high-speed communication, quantum information processing, and 3D sensing due to their excellent beam quality and low power consumption. However, generating high-purity and controllable circularly polarized light usually requires external optical components such as quarter-wave plates, which undoubtedly increases system complexity and volume, hindering chip-level integration. To address this issue, we propose a monolithic integration scheme that directly integrates a custom-designed double-layer asymmetric metasurface onto the upper distributed Bragg reflector of a chiral VCSEL. This metasurface consists of a rotated GaAs elliptical nanocolumn array and an anisotropic grating above it. By precisely controlling the relative orientation between the two, the in-plane symmetry of the structure is effectively broken, introducing a significant optical chirality response at a wavelength of 1550 nm. Numerical simulations show that this structure can achieve a near 100% high reflectivity for the left circularly polarized light (LCP), while suppressing the reflectivity of the right circularly polarized light (RCP) to approximately 33%, thereby obtaining an efficient in-cavity circular polarization selection function. Based on this, the proposed VCSEL can directly emit high-purity RCP without any external polarization control components. This compact circularly polarized laser source provides a key solution for achieving the next generation of highly integrated photonic chips and will have a profound impact on frontier fields such as spin optics, secure communication, and chip-level quantum light sources. Full article

Integrating metasurface-based polarizing filters atop photodetectors enables the expansion of detection capabilities from intensity to polarization, offering significant potential for applications requiring high-precision discrimination in scientific, industrial, and defense sectors. However, such metasurfaces often introduce optical efficiency losses. Here, we present a long-wave infrared (8.6 μm) circularly polarized photodetector capable of direct chiral discrimination, eliminating the need for additional optical components. The polarization selectivity arises from Guided-Mode resonances (GMRs) excited by two horizontally offset right-trapezoidal unit cells within a chiral metasurface. This design exhibits a pronounced transmittance contrast (~100%) between left circularly polarized light (LCP) and right circularly polarized light (RCP) while maintaining fabrication simplicity via a conventional single-step lithographic process. The proposed detector is expected to achieve high-dimensional physical characterization by resolving polarization-encoded vectorial information, demonstrating enhanced performance in complex environments. Full article