This work reports that the coupling of dual-band quasi-bound states in the continuum (qBICs) in an all-dielectric metasurface composed of periodic silicon nanodisks can be tuned from the collective electromagnetically induced transparency (EIT) like effect to the Rabi splitting by adjusting the lattice period or the nanodisk diameter. These two qBIC modes are out-of-plane toroidal dipole resonance and electric dipole surface lattice resonance, which are not allowed to emit at point. When the lattice period decreases or the nanodisk diameter increases, these two qBICs experience different spectral shifts and spectrally overlap when they have larger quality factors, resulting in enhanced coupling strength that transits from the weak- to the strong-coupling regime. Specially, in the weak coupling regime, the slow-light effect accompanied with the EIT-like phenomenon can be tuned by the quality factor. Our findings open a new paradigm for regulating the coupling of qBICs, which could find applications in lasing, nonlinear optics, and biochemical sensing.

Bound states in the continuum (BICs) in periodic nanophotonic structures provide a powerful route to achieving ultrahigh-Q resonances and strong light-matter interactions. However, controllable interconversion between different classes of BICs remains challenging. Here, we propose and experimentally demonstrate a dual-lattice metasurface platform that enables the systematic conversion between symmetry-protected BICs and accidental BICs through lattice hybridization and dipolar interference. By introducing two square lattices with either a relative in-plane displacement or a controlled size detuning of the central elements, we reveal two independent yet physically equivalent pathways to tailor the interference between electric and magnetic dipolar resonances. This interference leads to the emergence of accidental BICs without requiring intricate geometric optimization, and further gives rise to electromagnetically induced transparency-like spectral features during the BIC transition. Experimental measurements show excellent agreement with numerical simulations. Our results provide clear physical insight into the origin of accidental BICs in hybridized lattices and establish a versatile strategy for engineering high-Q resonances in metasurfaces with potentials for diverse applications. (c) 2026 Chinese Laser Press

We report spatiotemporally tunable mode coupling between Fabry-Pérot (F-P) resonances and dark or bright modes in the weak- or strong-coupling regime in an all-dielectric coupled system, which consists of an F-P microcavity formed by two distributed Bragg reflectors (DBR) and a metasurface made of periodic nanocavities. Simulation results show that F-P resonances can be tuned to be coupled to dark waveguide modes or a bright electric dipole Mie surface lattice resonance, depending on the microcavity height, and that the coupling strength can be manipulated between the weak- and strong-coupling regimes by varying the photon lifetime, or equivalently the quality factors (Q-factors) of F-P resonances, which can be realized by changing the number of DBR layers. We also show that the slow-light effect associated with the electromagnetically induced reflection-like window in the weak-coupling regime can also be regulated through the Q-factor. With all these findings, our study provides an alternative for manipulating light-matter interactions in coupled micro-/nano-cavities that are promising for various applications.

Fluorescence probes are the primary tools for monitoring mitochondrial membrane potential (MMP), a key indicator of mitochondrial function and cellular health. Although metasurfaces offer significant potential for enhancing fluorescence biosensing, all-dielectric metasurfaces with their inherent advantages remain largely unexplored for this application. Here, we demonstrate a fluorescence probe for MMP dynamics, significantly enhanced by an all-dielectric metasurface. Designed to support bound states in the continuum (BICs) via folded Brillouin zones, this metasurface achieves both a high quality factor and strong near-field enhancement. Experiments reveal an order-of-magnitude fluorescence intensity enhancement for cells on the metasurface compared to those off it, irrespective of forskolin stimulation. This approach enables dynamic monitoring of cellular health through MMP fluctuations at subthreshold concentrations.

Optical metasurfaces are planar arrays of engineered subwavelength nanostructures, and have emerged as a revolutionary platform for manipulating the light–matter interactions. Recently, vertical stacking of two or more metasurface layers has become a powerful and universal strategy for multifunctional optical field manipulation. By introducing additional degrees of freedom, such as interlayer spacing, twist angle, and lattice mismatch, multilayer metasurfaces enable unprecedented optical responses without altering the constituent materials or unit cell geometries. This structural versatility has significantly accelerated the advancement of multifunctional and reconfigurable photonic devices. This review provides a comprehensive overview of multilayer metasurfaces operating in the visible to near-infrared regime, with an emphasis on their physical mechanisms, structural evolution, fabrication methodologies, and applications. We summarize some recent breakthroughs across several frontier applications, including high-resolution imaging, optical information encoding, biosensing, and laser emission enhancement. In addition, we identify key challenges in material selection, inverse design, and scalable integration, and discuss future directions toward dynamic, large-area, and intelligent metasurface systems. Finally, we outline the promising role of multilayer metasurfaces in next-generation photonic platforms, smart imaging technologies, and all-optical information processing systems.

Slow light is a fascinating research area that is of fundamental interest and has enabled diverse applications. Electromagnetically induced transparency (EIT), or its analogies, and flat band are two distinct approaches to realize the slow light effect in photonic systems. Here, these two methods are combined and propose a flatband‐enhanced collective EIT‐like slow‐light effect in all‐dielectric kagome metasurfaces. The Q ‐factor, the group index, and the near‐field electric‐field enhancement can be significantly improved for the collective EIT‐like window enhanced by a flatband, compared to the one without such enhancement, are shown. The simulated transmittance spectra showing these EIT‐like windows are experimentally demonstrated. Making use of these collective transparency windows, bulk sensitivities up to 405 and 410 nm/RIU can be numerically obtained. Remarkably, by reducing the nanodisk size, an extremely large group index of 16 105 and high near‐field intensity enhancement of 8220 can be obtained for such a silicon kagome metasurface. This work is expected to provide a new direction for realizing strong slow light effect in metasurfaces with promising applications in biochemical sensing, nanolasing, and nonlinear optics.

The coupling between dual-band or multi-band quasi-bound states in the continuum (q-BICs) is of great interest for their rich physics and promising applications. Here, we report tunable collective electromagnetic induced transparency-like (EIT-like) phenomenon due to coupling between dual-band collective electric dipolar and magnetic quadrupolar q-BICs, which are supported by an all-dielectric metasurface composed of periodic tilted silicon quadrumers. We show that this collective EIT-like phenomenon with a strong slow light effect can be realized by varying the nanodisk diameter or the tilt angle and that the transparency window wavelength, the quality factor, and the group index can all be tuned by changing the nanodisk size. We further find that as the nanodisk size decreases, the slow light effect becomes stronger, and higher sensitivity can be obtained for the refractive index sensing. Interestingly, the sensitivity first increases exponentially and then reaches a plateau as the nanodisk size decreases, or equivalently as the group index increases. We, therefore, expect this work will advance the understanding of the collective EIT-like effect due to coupling between q-BICs, and the findings will have potential applications in slow-light enhanced biochemical sensing.

The metasurface analogue of electromagnetically induced transparency (EIT) provides a chip-scale platform for achieving light delay and storage, high Q factors, and greatly enhanced optical fields. However, the literature relies on the coupling between localized and localized or localized and collective resonances, limiting the Q factor and related performance. Here, we report a novel approach for realizing collective EIT-like bands with a measured Q factor reaching 2750 in silicon metasurfaces in the near-infrared regime, exceeding the state of the art by more than 5 times. It employs the coupling between two collective resonances, the Mie electric dipole surface lattice resonance (SLR) and the out-of-plane/in-plane electric quadrupole SLR (EQ-SLR). Remarkably, the collective EIT-like resonance can have diverging Q factor and group delay due to the bound state in the continuum characteristics of the in-plane EQ-SLR. With these findings, our study opens a new route for tailoring light flow in metasurfaces.

All-Dielectric Metasurface for Biosensing Applications All-dielectric metasurfaces support high-Q resonances, and they are free from heating and thus analyte damaging suffered from plasmonic counterparts, but have relatively low sensitivities due to large energy confinement within the high-index materials. In article number 2400425, Guangyuan Li and Yunhui Liu propose a new type of all-dielectric metasurface supporting nonlocal quasi-bound states in the continuum formed from the destructive interference of Mie surface lattice resonances. The authors demonstrate the suitability of this metasurface for biosensing applications due to the significantly and homogeneously enhanced near fields over large volumes.

We experimentally demonstrate the tuning of accidental bound states in the continuum (A-BICs) in silicon nanodisk arrays. The A-BIC emerges of the destructive interference of multipoles, which are the dominating out-of-plane electric dipole and in-plane magnetic dipole, and weak electric quadrupole and magnetic quadrupole. We further show that the spectral and angular position of the A-BIC can be conveniently tuned by varying the nanodisk size or the lattice period. Remarkably, the angular position can be tuned even to 0°, suggesting an interesting transition of the A-BIC from an off-Γ-BIC to an at-Γ-BIC. Our work provides a new strategy for light trapping with high quality factors, and the obtained tunable A-BICs can find potential applications in low-threshold lasing, enhanced nonlinear optics, and optical sensing.

We propose and demonstrate a single-pixel imaging method based on deep learning network enhanced singular value decomposition. The theoretical framework and the experimental implementation are elaborated and compared with the conventional methods based on Hadamard patterns or deep convolutional autoencoder network. Simulation and experimental results show that the proposed approach is capable of reconstructing images with better quality especially under a low sampling ratio down to 3.12%, or with fewer measurements or shorter acquisition time if the image quality is given. We further demonstrate that it has better anti-noise performance by introducing noises in the SPI systems, and we show that it has better generalizability by applying the systems to targets outside the training dataset. We expect that the developed method will find potential applications based on single-pixel imaging beyond the visible regime.

Collective lattice resonances (CLRs) and bound states in the continuum (BICs) are two exciting approaches for achieving high quality factors in metasurfaces. BICs emerging from CLRs have raised great interest for not only the ultrahigh quality factors but also the nonlocal field enhancement. However, experimental demonstrations remain insufficient due to the material absorption or the inappropriate parameter design. Here we experimentally demonstrate dual-band symmetry-protected BICs emerging from Mie CLRs in all-dielectric metasurfaces. We attribute these dual-band BICs to the zero emission at Γ point for the in-plane electric quadrupole and out-of-plane magnetic dipole CLRs, respectively. Such BICs feature nonlocal field enhancement and convenient spectral tunability, which are inherent to CLRs. We expect such nonlocal metasurfaces supporting BICs to find applications especially in nanolasers, nonlinear optics, and biochemical sensing.

In this paper, a high-precision frequency synchronization scheme in free space based on microwave photonic architecture is proposed, which can be used between multi-nodes in relative motion or in a motionless state. The reference frequency is modulated to high frequency through microwave photon up-conversion, and the reference signal is recovered at the receiver through photonics self-mixing technology. The experiment over free space in the laboratory in 4m, shows that the performance of Allen variance is s under the noise floor is s, and it is better than that of the electrical generation method with the Allen variance is s. The impact of system signal-to-noise ratio (SNR) on frequency stability is analyzed, and the experimental results are consistent with the theoretical value. At the same time, a functional experiment based on free space RF synchronization is conducted, compared to the direct synchronization method, the phase degradation of this method is only 0.25 rad, and the degradation of peak side lobe ratio (PLSR) of pulse compression loss is 0.29 dB. The good, coherent result further verifies the correctness of this synchronization method.

There are numerous applications of terahertz (THz) imaging in many fields. However, current THz imaging is generally based on scanning technique due to the limited intensity of the THz sources. Thus, it takes a long time to obtain a frame image of the target and cannot meet the requirement of fast THz imaging. Here, we demonstrate a single-shot direct THz imaging strategy based on a broadband intense THz source with a frequency range of 0.1~23 THz and a THz camera with a frequency response range of 1~7 THz. This THz source was generated from the laser–plasma interaction, with its central frequency at ~12 THz. The frame rate of this imaging system was 8.5 frames per second. The imaging resolution reached 146.2 μm. With this imaging system, a single-shot THz image for a target object with a size of more than 7 cm was routinely obtained, showing a potential application for fast THz imaging. Furthermore, we proposed and tested an image enhancement algorithm based on an improved dark channel prior (DCP) theory and multi-scale retinex (MSR) theory to optimize the image brightness, contrast, entropy and peak signal-to-noise ratio (PSNR).

Plasmonic nanoantennas containing nano-gaps support "hotspots" for greatly enhanced light-matter interactions, but suffer from inherent high losses, a long-standing issue that hinders practical applications. Here we report a strategy to significantly suppress the losses of plasmonic dimer nanoantennas. Specifically, by introducing the concept of cooperative near- and far-field coupling, we observed an unprecedented transition from the weak coupling of localized resonances to strong coupling of collective (nonlocal) resonances, showing robustness to the gap distance between the dimer. We develop a generalized lattice sum approximation model to describe this transition and reveal its origins: the off-diagonal element of the anisotropic polarizability tensor due to near-field coupling, and the anisotropic lattice sums due to far-field coupling. This strong coupling leads to loss-suppressed plasmonic resonances with large modulation depths and meanwhile extremely high measured quality factors up to 3120 in the near-infrared regime, exceeding the record in the near infrared regime. Additionally, high-Q and large chiroptical responses can also be induced for achiral planar dimers under the critical coupling condition. This work paves an avenue toward extremely low-loss plasmonic devices, either chiral or not, for diverse important applications.

Controllable large-scale integration of two-dimensional (2D) materials with organic semiconductors and the realization of strong coupling between them still remain challenging. Herein, we demonstrate a wafer-scale, vertically layered SnSe2/PTAA heterojunction array with high light-trapping ability via a low-temperature molecular beam epitaxy method and a facile spin-coating process. Conductive probe atomic force microscopy (CP-AFM) measurements reveal strong rectification and photoresponse behavior in the individual SnSe2 nanosheet/PTAA heterojunction. Theoretical analysis demonstrates that vertically layered SnSe2/PTAA heterojunctions exhibit stronger C-Se covalent coupling than that of the conventional tiled type, which could facilitate more efficient charge transfer. Benefiting from these advantages, the SnSe2/PTAA heterojunction photodetectors with an optimized PTAA concentration show high performance, including a responsivity of 41.02 A/W, an external quantum efficiency of 1.31 × 104%, and high uniformity. The proposed approach for constructing large-scale 2D inorganic-organic heterostructures represents an effective route to fabricate high-performance broadband photodetectors for integrated optoelectronic systems.

All-dielectric metasurfaces supporting high-Q resonances have emerged as a promising platform for sensing applications. However, the greatly enhanced near-fields are usually confined within the all-dielectric nanostructures rather than the outside analyte region, severely limiting the bulk sensitivity and the biosensing performance. Here, a silicon metasurface formed by the hybridization of two lattices with a relative displacement is designed to support nonlocal quasi-bound states in the continuum (q-BICs) featuring homogeneous and significant near-field enhancement over large volumes outside the silicon nanodisks. A high bulk sensitivity of 407 nm RIU-1 is experimentally demonstrated for the refractive index sensing applications, and a limit of detection down to 20 pg mL-1 for a protein biomarker for the early-stage breast cancer screening, which is improved by more than an order of magnitude over the state of the art. It is expected that the nonlocal q-BICs open new opportunities for realizing greatly enhanced light-matter interactions over large volumes in applications beyond biochemical sensing. Silicon metasurface supports nonlocal bound state in the continuum featuring homogeneous and significant near field enhancement in the analyte region, leading to ultra-low limit of detection down to 20 pg mL-1 for breast cancer biomarker, which is more than an order of magnitude lower than the state of the art. image

Plasmonic Metasurfaces with Quality Factors Up to 790 in the Visible Regime In article number 2301205, Guangyuan Li and co-workers demonstrate that by adopting short nanorods, plasmonic metasurfaces supporting lattice resonances under oblique incidence have significantly enhanced quality factors and near fields extending over large volumes, providing an exciting platform for ultrastrong light-matter interactions in diverse applications.

准连续域束缚态(Quasi-BIC)是超表面中一种特殊共振模,具有极高的品质因子,可以极大地提高光与物质的相互作用,在荧光增强、纳米激光、光传感以及非线性光学等领域均有重要应用.本文基于我们前期对quasi-BIC产生的理论,研究quasi-BIC介质超表面在折射率传感方面的应用.本文给出了传感系统的基本结构,利用电子束光刻技术结合注塑工艺完成了样品光流控结构的制备,并初步测试性能.研究结果表明,得益于产生quasi-BIC的新方法,该超表面具有两个高Q值quasi-BIC共振峰(1.523 μm和 1.570 μm,品质因子分别为 3069和 4071).以四种折射率溶液(n分别为1.450/1.462/1.470/1.480)为样品的测试实验表明,两个共振峰均能完成折射率检测,灵敏度S分别为452 nm/RIU、428 nm/RIU,性能评价指标FOM分别为376.7、372,优于现有文献;共振波长和折射率之间线性度良好,展现了quasi-BIC超表面在折射率传感中的应用潜力.

Plasmon metasurfaces supporting surface lattice resonances (SLRs) have emerged as an exciting platform for manipulating nanoscale light‐matter interactions in expanding applications. Although great progress has been achieved, the quality factors of plasmonic metasurfaces remain quite limited especially in the visible regime, hindering practical applications. This study reports an SLR‐based plasmonic metasurface with an ultrahigh quality factor that reaches 1427 in theory and 790 in experiments at 712 nm, a 240% increase over the state of the art. The quality factor of the out‐of‐plane SLR in periodic gold or silver nanorods is augmented by an order of magnitude through reducing the nanorod height from 100 to 50 nm. With these findings, this work is expected to pave the way for realizing high‐performance nanolasers, nonlinear frequency converters, and biosensors based on ultrahigh‐ Q plasmonic metasurfaces.