Flat optical metasurfaces are transforming photonics research by enabling new ways to control light in ultrathin, versatile photonic devices. The rise of quasi-bound states in the continuum (qBIC) metasurfaces has enabled tailored high-quality (Q) factor resonances in subwavelength nanostructured thin films, analogous to traditional optical cavities. In this perspective, we explore the emergence of cavity quantum electrodynamics (QED) in optical qBIC metasurfaces, specifically those constructed from van der Waals (vdW) layered materials. Because of their remarkable properties, vdW metasurfaces can support intrinsic optical resonances within the same active material hosting luminescent species, such as excitons or defects, leading to optimal light-matter coupling. This approach of self-hybridizing the cavity-emitter system into a single platform effectively overcomes limitations in on-chip integration of conventional cavities. Combining vdW materials with optically engineered qBIC metasurfaces opens exciting possibilities for exploring nanoscale light-matter interactions. Moreover, the distinctive features of vdW materials, from vertical heterostructures to twist-angle-dependent properties, offer a unique platform bridging the condensed matter physics of 2D materials and engineered nanophotonics. We propose that harnessing strong light-matter coupling in vdW-integrated qBIC metasurfaces will pave the way for next-generation nanoscale polaritonic devices.
The inherently weak nonlinear optical response of bulk materials remains a fundamental limitation in advancing photonic technologies. Nanophotonics addresses this challenge by tailoring the size and morphology of nanostructures to manipulate the optical near field, thus modulating the nonlinear response. Here, we explore a complementary strategy based on engineering the electronic band structure in the mesoscopic regime to enhance optical nonlinearities. Specifically, we demonstrate an increase in second-harmonic generation (SHG) from crystalline silver films as their thickness is reduced down to just a few atomic monolayers. Operating at the boundary between bulk and two-dimensional systems, these ultra-thin films exhibit a pronounced enhancement of SHG with decreasing thickness. This enhancement stems from quantum confinement effects that modify the interaction between electronic states and incident light, which we explain based on quantum-mechanical calculation. Our atomically-thin crystalline silver films provide a new means to overcome the small interaction volumes inherent to nanophotonic platforms, enabling efficient nanoscale nonlinear optics with potential applications in photonics, sensing, and quantum technologies.
A spherulite is a radially symmetric, microscale crystalline aggregate formed by molecular self-assembly, typically exhibiting concentric birefringent textures under polarized light, which is highly sought after for optical applications, especially in structured light generation and modulation. In this work, we exploit the optical properties of spherulites formed by 7OCB molecules. Radially aggregated needle-like 7OCB crystals result in a strong anisotropic transmittance with respect to radial and azimuthal orientations due to scattering loss over a wide range. Thus, polychromatic generation of cylindrical vector optical vortex beams across a broad spectrum from visible to near infrared, as well as a noncoherent white light optical vortex beam, is realized via spin-to-orbital angular momentum conversion from the spherulite. This approach opens promising opportunities for employing spherulites in structured-light generation and in the modulation of both polarization and angular momentum.
Metasurfaces enable diverse applications by controlling light's amplitude, phase, and polarization. Although deep learning-based inverse design has revolutionized metasurface design, current models are limited by fixed operating conditions and lack universality, often requiring retraining for new wavelengths, polarizations, or application scenarios. To address this, we introduce MetasurfaceViT (Metasurface Vision Transformer), a generic AI model for inverse design. Our solution leverages a large dataset of Jones matrices, significantly expanded via physics-informed data augmentation. By pretraining through masking wavelengths and polarization channels, MetasurfaceViT can reconstruct full-wavelength Jones matrices, which are then used by a fine-tuning model for inverse design. This versatility allows one-shot structure design for arbitrary wavelength, polarization, and application requirements. We demonstrate MetasurfaceViT's capabilities in designing multiplexed printings and holograms and broadband achromatic metalenses. Prediction accuracy exceeds 99% for physically realistic designs, showcasing a significant step toward a universal optical inverse design paradigm.
Smart optical solar reflectors (OSRs) with temperature-adaptive radiative emission around room temperature are highly desirable for passive thermal management in spacecraft. This work demonstrates a smart and flexible metasurface-based OSR, or meta-OSR, consisting of an optimized W:VO2-based metasurface and a low emissivity solar reflector. The fabricated smart meta-OSR overcomes long-standing challenges by combining a solar absorption (α) of 0.22, high-temperature emissivity (ε hot) of 0.8, infrared emissivity contrast (Δε) of 0.33 and a transition temperature (T MIT) of 30°C. In addition, through the use of nanoimprint lithography and a low-temperature W:VO2 process, the smart meta-OSR is demonstrated over an area of 10 × 10 cm2 on space-grade polyimide, achieving significant weight reduction and easy integration on satellite surfaces. The fabricated devices successfully passed various space qualification tests, including thermal cycling, proton and electron radiation, adhesion, bending and humidity resistance, showing negligible performance degradation. The smart meta-OSRs in this work are production-ready and hold promise as next-generation thermal control solution for ultralight spacecraft and small satellites.
Skyrmionic patterns of optical fields have recently emerged across diverse photonic platforms. Here, we show that such textures also arise in the polarization eigenstates of light propagation through flat dielectric devices with an engineered, space-dependent optic axis orientation. We focus on two-dimensional periodic structures, where propagation through multiple devices maps onto quantum dynamics on a synthetic optical lattice. Adopting the condensed-matter framework, a spatial period defines an effective Brillouin zone, and polarization eigenstates can be grouped in two bands, with the role of energy played by the opposite phase delay. When such eigenstates exhibit skyrmionic textures, the corresponding lattice model shows the topology of a Chern insulator. We validate these concepts in a system of three tunable liquid-crystal metasurfaces. Using machine learning, polarization eigenmodes are reconstructed over one spatial period. We identify configurations of the devices' parameters that lead to topologically nontrivial bands, where we directly observe skyrmionic eigenpolarization textures. We also extract local observables of lattice models, such as the Berry curvature and the quantum metric. We finally report a numerical simulation of an all-optical quantum Hall effect emerging when light propagates through a sequence of such devices, arranged to mimic the effect of an external force on the lattice.
Non-Hermiticity has introduced new physical mechanisms into sensing, with approaches based on exceptional points and non-Hermitian skin effects demonstrating potential sensitivity enhancements over conventional sensing technologies. By monitoring the frequency shifts of specific eigenmodes, previous studies on non-Hermitian sensors have revealed extraordinary sensitivity to local perturbations. In contrast, the influence of global perturbations such as noise and disorder, which generally involve complex spectra and may even suppress these eigenmodes, seems largely incompatible with the current non-Hermitian sensing framework and has received far less attention. Here, motivated by recent theoretical advances on pseudospectra theory, we investigate the possibility of employing maximum transient growth to probe the level of global perturbations in non-Hermitian skin-effect sensors. Using discrete-time light walks in synthetic photonic lattices, we experimentally evaluate the performance of a non-Hermitian photonic lattice under static global phase noise. Remarkably, we demonstrate that the sensitivity grows exponentially with lattice size, manifesting in the maximum transient growth rather than the spectral shifts of previous non-Hermitian skin-effect sensors. Furthermore, numerical simulations reveal that this exponential sensitivity is preserved under dynamical perturbations. Our results highlight the limits as well as the potential of non-Hermitian systems to tackle a wide range of sensing requirements for next-generation ultrasensitive sensors.
The super-resolution technique based on random laser (RL) achieve the spectra that break through the frequency resolution limit of the original spectrometer. However, the speed of super-resolution spectrometer methods based on RL is limited by the time-consuming need to record many thousands of sub-resolution sparse spectral frames. Here, we propose a deep learning super-resolution spectrometer based on fiber random laser with ultrahigh spectral purity, obtaining super-resolution images from up to an 80% reduction in reconstruction time compared with what is usually needed. By coupling to a nested fiber microcavity, the decay rates of RL quasi-modes broaden, resulting in an excellent micro-nano light source for a super-resolution spectrometer showing high spectral purity, good directivity, and a miniature size. Based on this micro-nano light source, the sparse frames for reconstructing super-resolution spectra decreased threefold compared with that reported before. Furthermore, a convolutional neural network is demonstrated to recover the super-resolution spectra from an 80% smaller number of raw frames or an 80% smaller density of localizations. The drastic reduction in the acquisition time of the super-resolution spectrometer promotes the development of integrated, low-cost, high-resolution spectroscopy with a small footprint.
The collective interactions of nanoparticles arranged in periodic structures give rise to high- Q in-plane diffractive modes known as surface lattice resonances. Although these resonances and their broader implications have been extensively studied within the framework of classical electrodynamics and linear response theory, a quantum optical theory capable of describing the dynamics of these structures, especially in the presence of material nonlinearities beyond ad hoc few-mode approximations, is largely missing. To this end, we consider a lattice of metallic nanoparticles coupled to the electromagnetic field and derive the quantum input-output relations within the electric dipole approximation. As applications, we analyze coupling between the nanoparticle array and external quantum emitters, and show how the formalism extends to molecular optomechanics, where the high Q -factors of SLRs enable coupling to collective vibrational modes. We further consider arrays composed of saturable excitonic emitters, demonstrating how emitter nonlinearities can be used to switch the SLR condition between electronic transitions. Using a perturbative approach that accounts for population dynamics, we show how these effects can be probed in pump-probe experiments and give rise to nonlinear phase-matching phenomena. Our work provides a microscopic framework for modeling SLRs interacting with quantum emitters without phenomenological descriptions of the electromagnetic environment.
Irregular-shaped perfect vector vortex beams (IPVVBs), as a novel form of structured light for optical field manipulation, have attracted significant attention due to their combined properties of spatial vectorization, orbital angular momentum control, and polygonal symmetry. Compared with traditional circularly symmetric vortex beams, IPVVBs offer notable advantages in mode control and freedom expansion, providing new possibilities for high-dimensional optical field encoding, optical manipulation, and information transmission. In this paper, using an all-dielectric metasurface designed with pure geometric phases, we achieve the generation and spatial polarization control of integer and fractional order irregular-shaped perfect vector vortex beams on the hybrid Poincaré sphere by introducing a cross-phase distribution. The proposed IPVVBs exhibit unique topological properties and stable propagation characteristics. Moreover, the designed metasurface exhibits excellent broadband performance, enabling efficient generation of IPVVBs across multiple wavelengths. Furthermore, we experimentally demonstrate the edge imaging capability of IPVVBs, achieving a resolution of up to 3.1 μm. This work opens up new research directions in cutting-edge fields such as modern optical imaging, microscopic manipulation, and quantum communication.
Exciton dissociation in semiconducting nanostructures is crucial for optoelectronic applications, especially when free-carrier generation is required. Despite considerable research, the question of whether and how such generation occurs in strongly excitonic systems remains elusive. Here, we use one-dimensional precision graphene nanoribbons (GNRs) as a model system to investigate exciton dissociation. We systematically explore the interplay between ribbon length (l), excitation energy, and band dispersion in various precision GNRs. Ultrafast Terahertz conductivity measurements reveal that hot exciton dissociation dominates carrier generation, with ribbon length significantly influencing free carrier lifetimes. We identify a critical Bjerrum length (RB) of approximately 20 nm that determines whether photoexcited hot carriers in GNRs can dissociate before forming tightly bound excitons. For shorter ribbons (l < 2RB), rapid ~ps exciton formation prevails. Furthermore, the charge-carrier band dispersion in GNRs plays a critical role in determining dissociation efficiency. Long GNRs with strongly dispersed bands, and consequently low effective carrier masses, exhibit higher mobilities that promote efficient hot-exciton dissociation. These results advance fundamental understanding of dimensionality, energetics, and electronic structure in excitonic materials, providing design principles for optoelectronic devices based on excitonic materials.
Surface phonon polaritons (SPhPs) enable nanoscale manipulation of mid-infrared light via deeply subwavelength topological vector textures, such as skyrmions. Achieving dynamic, real-time control over these topological features remains challenging. Here, we theoretically propose and numerically demonstrate an actively tunable platform on a silicon carbide membrane that creates lattices of diverse topological textures, including skyrmions, merons, and skyrmion bags. By exploiting the sublinear SPhP dispersion, we dynamically adjust the excitation wavelength to tune the topological character of these lattices. This enables tunability between bubble-type and Néel-type configurations, controlling field confinement and topology for topological textures in the electric field and the spin angular momentum. Furthermore, we identify a novel singularity-type meron arising from the interplay of electric and magnetic spin components. This texture exhibits topological charge conservation in moiré superlattices and a spatially confined spin reversal with tunable lateral sizes as low as λ SPhP / 29 and skyrmion number density confinements as low as λ SPhP / 64 . These findings provide a versatile framework for on-chip, reconfigurable topological photonic devices with potential applications in high-resolution imaging and precision metrology in the mid-infrared. The results can be readily extended to other topological systems, where similar dispersion relations hold.
In the Research Article (DOI: 10.1002/nap2.70000), Yang Hu, Xiuquan Huang, Pablo Alonso-González, and co-workers investigated near-field radiative heat transfer between two separated twisted α-MoO3 bilayers and found that the heat flux can be enhanced by simply increasing the interlayer twist angle. This modulation is attributed to the emergence of topological transitions, shifting from open (hyperbolic) to closed (elliptical) polaritonic dispersions. This work offers theoretical insights into the modulation of NFRHT using twistoptics, representing a significant step toward the advancement of twisted thermotics.
Spectroscopic single-molecule localization microscopy (sSMLM) simultaneously acquires both spatial and spectral information from fluorescent molecules, facilitating molecular characterization analysis and multicolor imaging. However, this technique poses a fundamental dilemma: a finite photon budget must be split between localization and spectroscopy, limiting the performance of both. To alleviate this trade-off, we propose orthogonally dispersed sSMLM (ODsSMLM). By modulating single-molecule emission spectra through an orthogonal structure, ODsSMLM allows all photons to be used for both localization and spectral characterization. Crucially, this approach provides isotropic lateral localization precision, effectively removing the inherent dispersion-dependent localization artifacts of other methods. Using simulated data, we demonstrate that under a 3000-photon budget, ODsSMLM attains a localization precision of 10 nm and a spectral precision of 1.1 nm. Moreover, in dual-color imaging experiments of microtubules and clathrin, ODsSMLM achieved isotropic lateral resolution of 27 nm.
The rapid progress of microwave imaging technology has made conventional camouflage materials with fixed absorption performance ineffective. As the imaging band expands, camouflage materials capable of broadband operation, especially in the S and the C band, dynamic modulation are required to hide targets in complex environments. Here, we propose a dynamically modulated camouflage metasurface employing deep-subwavelength slots to enhance multiband modulation capability. By varying the vertical displacement of the structure, reflectivity can be modulated from below -10 dB to near 0 dB over 2.7-19.1 GHz (150.4% relative bandwidth), while maintaining insensitivity to the incidence angle and polarization. An equivalent interface-impedance model is established to reveal the mechanism of slot-enhanced low-frequency resonance. The laser processing parameters are optimized to reduce the slot width to 25 μm (λ max/4440), enabling broadband dynamic modulation, as experimentally verified. Benefiting from its broadband dynamic modulation performance extending to the S and the C band, the proposed camouflage metasurface demonstrates potential for countering emerging microwave imaging technologies.
The image shows an artistic depiction of the out-of-plane electric field component of a moiré skyrmion superlattice. This lattice harbors skyrmion bags as complex multi-skyrmion topological excitations. The field distribution is obtained by interfering surface phonon polariton waves on a silicon carbide membrane. On this platform, the topological character of the skyrmion bags can be tuned between bubble- and Néel-type, due to the fully accessible sublinear dispersion of the surface phonon polaritons. More details can be found in the Research Article by Julian Schwab and co-workers (DOI: 10.1002/nap2.70015).
Optical neural networks leverage the inherent parallelism of light to multiplex across various degrees of freedom including wavelength, polarization, and modes. Among these, orbital angular momentum (OAM), possessing a theoretically infinite number of orthogonal mode dimensions, holds significant potential for constructing optical neural networks. However, OAM conversion and multiplexing on integrated photonic chips remain challenging. Here, we present an on-chip OAM mode converter and multiplexer device based on inverse design. The OAM mode converter achieves maximum up-conversion efficiency of 88.68% ( OAM - 1 → - 2 ), maximum down-conversion efficiency of 88.04% ( OAM - 3 → - 1 ), and maximum modulation depth of 4.07 dB ( OAM + 1 → + 3 ). Besides, the OAM ± 1 , ± 2 multiplexer achieves maximum conversion efficiency of 98.29% and maximum modulation depth of 20.69 dB. Subsequently, we demonstrate an OAM-encoded hybrid optical convolutional neural network built using this device, achieving 98.0% accuracy on MNIST handwritten digit recognition and 86.1% accuracy on Fashion-MNIST classification. This device provides a novel approach for on-chip OAM conversion and multiplexing while also enabling on-chip optical convolution operations by using OAM mode. This work offers a practical pathway for integrating OAM with on-chip optical neural networks.
Bound states in the continuum (BICs) are waves exhibiting theoretically infinite quality factors, offering a powerful mechanism for extreme light confinement in photonic structures. Although breaking vertical structural symmetry in BICs-supporting systems can induce asymmetric radiation, the radiated power typically remains partitioned between opposing half-spaces. Furthermore, achieving arbitrary control over the amplitude ratio and phase difference of these counter-propagating beams presents a significant challenge, thereby limiting sophisticated beam manipulation within a single half-space. In this work, we delve into BICs within the superwavelength regime, where photonic structures inherently support multiple diffraction orders. We systematically investigate the far-field polarization states and associated topological properties of these individual diffraction channels. Critically, by engineering a configuration that supports two co-propagating diffraction orders directed into the same half-space, we demonstrate comprehensive and continuous control over the resulting unidirectional guided resonances (UGRs). Full tunability of both the directionality (spanning from -1 to 1) and the relative phase difference (spanning from -π to π) between these two co-propagating beams is achieved. This versatile manipulation of multiple beams radiating concertedly into a specific direction opens new avenues for various advanced applications.
Fermi-arc metals, unconventional semi-metals featuring cylindrical Fermi surfaces formed by Fermi arcs, have recently attracted extensive attention for realizing a novel metallic phase that retains chiral anomaly responses yet suppresses quantum oscillations. Although it was proposed that spatially twisting a superlattice of thin Weyl metals can form a Fermi-arc metal, previous local-approximation analyses are valid only for slowly varying systems and cannot capture all rich physics in such systems. Here, we report an optical realization of such a phase in a natural magnetized plasma subjected to a helically modulated magnetic field. Unlike previous studies on artificial heterostructure platforms, we admit a fully analytical, nonperturbative treatment that tracks a complete evolution of Weyl node. In the slowly varying regime, our platform faithfully realizes and manipulates the Fermi-arc metal state in a real system. As the modulation rate increases, Fermi-arcs inheriting opposite chiralities start to hybridize. Remarkably, in the deep nonperturbative limit, chirality vanishes, not through the conventional Weyl point annihilations, but via Fermi arc recombination, resulting in a chirality-free uniaxial optical medium. These findings unveil global topological transitions in nonuniform Weyl systems and open routes toward photonic devices based on engineered Fermi-arc dynamics.