Zhongzhu Liang

Bound states in the continuum (BIC) have been extensively studied, as they facilitate multi-band resonance. However, current research lacks the distinction of the individual contributions of different symmetry-breaking mechanisms. Specifically, how translational symmetry, point-group symmetry, and the coupling strength respectively achieve the excitation and regulation of quasi-BIC (QBIC), this issue still requires a clear understanding. This study addressed this issue by designing a series of different geometric structures and analyzing the resonant peaks and electromagnetic field images they generated. We designed a metasurface composed of Ge square pillars. Through a single geometric parameter, the symmetry of the structure can be controlled. The physical mechanism of symmetry-breaking was systematically elucidated. The study showed that translational symmetry determines the spectral framework of the modes, point-group symmetry controls the selection of the modes and the field distribution, and coupling strength independently regulates the broadening and interaction of the modes. Based on this collaborative regulation model, the resonances of multiple QBIC modes can be adjusted. Additionally, by utilizing the differences in the electromagnetic field distribution of each mode, highly specific and multi-parameter sensing of environmental refractive index, temperature, and adsorption layer thickness was achieved.

Improving absorption, broadening bandwidth, and enhancing polarization sensitivity are central objectives in current research. We propose a long-wave infrared metamaterial absorber based on a ring-grating composite structure that provides broadband absorption and high polarization sensitivity. The absorber is functionally designed with a top resonator and a bottom reflector. The underlying continuous metal layer is replaced with an anisotropic metal grating to enable polarization-sensitive reflection. The top adopts a geometrically symmetrical ring resonant structure to broaden the absorption bandwidth. The maximum absorptance under TM polarized light incidence is greater than 99.9%, and the absorptance under TE polarized light incidence is less than 3%, with a maximum extinction ratio of 56. We also demonstrate stable performance under oblique incidence. This design presents a novel approach for broadband polarization-sensitive absorbers.

The advancement of compact and wearable optical systems is critically limited by the lack of high‐performance, integrable solutions for managing stray light, particularly in the mid‐infrared regime. Traditional approaches relying on bulky baffles or cryogenic cooling hinder miniaturization and flexibility. Herein, we report a large‐area, flexible metamaterial film based on a Ti/Al ₂ O ₃ /Fe ₃ O ₄ /Ti heterostructure that functions as an ultra‐broadband infrared extinction layer. By introducing a lossy Fe ₃ O ₄ interlayer, our design achieves an exceptional average absorptivity of 97.1% across the 3–5 µm atmospheric window, with a total thickness below 1 µm. This “loss engineering” strategy effectively broadens the absorption bandwidth and smoothens the spectral response compared to conventional metal‐insulator‐metal(MIM) absorbers. The film is fabricated on a flexible polyimide substrate via scalable lithography, demonstrating remarkable mechanical robustness. More importantly, we integrate it into a practical optical system as a cylindrical baffle, where it suppresses stray light intensity to a mere 0.6% after three reflections, significantly enhancing imaging contrast. This work presents not merely a high‐performance absorber, but a scalable, flexible material platform that paves the way for next generation miniaturized and flexible optical devices.

Optical metasurface sensors play a significant role in fields such as biochemical sensing and environmental monitoring. Bound states in the continuum (BIC) is a commonly used method to achieve high quality (Q) factors in recent years. However, how to maximize the Q value in the actual structure remains a key challenge. Here, we propose a mid-infrared all-dielectric metasurface sensor based on asymmetric "internally cut four-hole" cylindrical meta-atoms. This structure creates a composite optical resonator with ultra-high quality factor and optical localization capability by fusing photonic crystal plates with cylindrical resonators. We successfully excite dual-band narrowband resonance, and systematically compare different symmetry-breaking strategies. Research has demonstrated that by exciting the magnetic dipole (MD) mode and adopting a superior symmetry-breaking scheme, higher Q value and high sensitivity can be achieved. The simulation and multipole analysis results confirmed the existence of MD and electric quadrupole (EQ) modes, ultimately achieving a Q factor of approximately 1.8 × 10⁵, sensitivity (S) of 1110 nm/RIU and 1478 nm/RIU, and excellent figure of merit (FOM) of 3500 RIU -1 and 6000 RIU⁻¹. This research provides an effective solution for the development of high-performance mid-infrared sensing chips.

With the improvement of precision in modern optical systems, the demand for the ability to eliminate stray light in the system is also increasing. However, traditional methods for eliminating stray light either utilize complex mechanical structures and black coatings, or reduce the emission of stray light through refrigeration, which hinders the miniaturization and lightweighting of the system, especially in infrared systems. To address this challenge, we demonstrate a large-area infrared broadband flexible extinction film designed with an ultra-thin structure, which can achieve 97.1% absorption in 3-5μm atmospheric windows, with a total film thickness not exceeding λ/6. This device achieves broadband absorption with a simple structure, enabling it to be integrated on large-area flexible substrates. It demonstrates excellent extinction performance, feasibility and repeatability of large-area processing, and can be applied in fields such as eliminating stray light, infrared stealth, and electromagnetic shielding.

Zoom lenses are essential for optical imaging applications. The development of metasurfaces offers an approach to overcoming the complexities and bulkiness of conventional zoom systems. Most current tunable zoom metalenses only adjust focus in axial or transverse directions and lack multi-dimensional light field adjustment capabilities. In this study, a dual-polarization responsive three-dimensional zoom metalens based on the Moiré lens effect was designed. The metalens can provide continuous three-dimensional control of the focal point by adjusting the rotation angles of the three metasurfaces, achieving micrometer-level positioning accuracy across the entire spatial range. Furthermore, the metalens exhibits phase modulation characteristics associated with chirality. Specifically, when the incident light is excited in different circular polarization states (right-handed and left-handed), it produces a focal field distribution that depends on the polarization state. This is important for acquiring multi-dimensional information and enhancing target features in complex scenes. The metalens achieves axial zoom ranges of 1–6.5× for right handed circularly polarized light and 1–5.7× for left-handed circularly polarized light, with lateral deflection angles of ±12.5° and ±15.4°, respectively. The focusing efficiencies reach 65.2% and 67.1% for right- and left-handed circularly polarized light. This dual-polarization three-dimensional zoom metalens shows great promise for machine vision, microscopic imaging, and dynamic three-dimensional tracking, advancing multifunctional integrated optical systems.

Vibrational strong coupling (VSC) has promising applications in chemical reactions, molecular spectroscopy, and biochemical sensing. VSC can be achieved using plasma nanostructures. However, effective coupling between plasma nanostructures and molecules is often hindered by the metal materials used. Dielectric metasurfaces offer significant advantages and can effectively excite VSC, but the implementation of VSC through dielectric metasurfaces has not been widely investigated. Here, a mid-infrared all-dielectric metasurface to realize strong coupling control driven by quasi-bound states in the continuum (QBIC) is proposed. By coupling with polymethyl methacrylate (PMMA) molecules, a significant spectral splitting occurred. A 50-nm-thick PMMA layer increases the molecular signal amplification factor to 91%. Adjusting structural asymmetry parameters and utilizing the high Q factor of the QBIC mode allows flexible modulation of the coupling state. A strong coupling phenomenon is also observed with an oscillator absorption strength (Δε) 0.02 and a 5 nm PMMA thickness. Refractive index sensing analysis indicates a sensitivity of 2118 nm RIU−1, with a maximum figure of merit of 4089 RIU−1. This study highlights the potential of vibrational strong coupling for advancing biochemical sensing and polaritonic chemistry applications.

Zoom metalenses operating in the ultraviolet band have high resolution and flexibility, which can achieve accurate imaging and detection of tiny objects. It is useful for applications requiring high-intensity ultraviolet light, such as photolithography in semiconductor manufacturing, cell imaging in biomedical field, ultraviolet imaging and detection, ultraviolet catalysis, etc. However, most zoom systems need double-layer structure or complex mechanical tuning mode, which makes it difficult to achieve miniaturization due to its large volume. Here, an all-dielectric single-layer zoom metalens in the ultraviolet band is designed by changing the polarization state of the incident light. The focal length, focal depth, and focusing efficiency of the metalens are discussed when different polarized light sources are incident. The metalens uses (AlxGa1−x)2O3 material to achieve continuous focal length control at the wavelength of 365 nm, and the focusing efficiency is maintained at about 80%. The zoom metalens has the advantages of small volume, compact surface, flexible control, and fine adjustment. It is widely used in small mobile devices, precision medical systems, advanced optical components, etc.

Optics metasurfaces have been utilized for research into computer-generated holography imaging and encryption due to their exceptional ability to manipulate fundamental properties of light waves, including polarization, amplitude, and phase. In this study, we proposed a dual-polarization channel (DPCs) meta-pixel to achieve infrared polarization-multiplexed meta-holography. By leveraging the Pancharatnam–Berry phase metasurface, we constructed and imaged the holographic phase information of “NENU” and the school badge at an infrared wavelength of 10.6 μm in the far field. The proposed meta-pixel, consisting of left-handed (LPC) and right-handed (RPC) circularly polarized channels, is designed to control the wavefront. The independence of the DPCs meta-pixel enables a single polarization channel to produce independent imaging. Furthermore, based on polarization decomposition and composition, the imaging intensity of the LPC and RPC reflects the ellipsometric properties of the polarization state. The relative phase and polarization conversion efficiency between LPC and RPC meta-atoms were carefully designed to enable full-polarization meta-holographic imaging. The results demonstrate that DPCs meta-pixels can operate independently or synergistically to achieve infrared polarization meta-holography. This work highlights the potential of infrared meta-holography, utilizing polarization information for enhanced security, and offers promising applications in infrared camouflage, information security, and communication.

Polarization is one of the fundamental properties of electromagnetic waves, and polarization devices based on metasurfaces have a wide range of potential applications in detection, communication, and other fields. Based on the phase in the orthogonal direction and rotation angle of the meta-atom and the metal grating embedded in the substrate, a universal method is proposed to control the polarization of the metasurfaces. Among them, the orthogonal phase provides the parameter of the diagonal position of the Jones matrix, and the rotation angle provides the parameter of the rotation matrix. The integration of embedded metal gratings simplifies the transmission matrix, further enabling arbitrary polarization adjustment. The metasurface integrating polarization selection, control, and multiplexing achieves simultaneous control and multiplexing of linear, circular, and elliptical polarizations. This research proposes an innovative approach to create highly integrated multifunctional metasurfaces and holds promise for polarization imaging and detection applications.