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 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.
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.
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.
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.
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.
The growing demand for massive and high-speed data processing within compact photonic circuits has highlighted a critical challenge: the efficient integration of high-quality ultrasmall light sources and emitters onto next-generation integration platforms. Despite notable advancements achieved through conventional and cutting-edge strategies, integration technologies utilizing the micro-transfer-printing technique-employing microstructured polymeric stamps, such as polydimethylsiloxane (PDMS)-have garnered considerable attention. This innovative approach facilitates heterogeneous integration by enabling the deterministic placement of micro- and nanoscale optical structures and materials with sub-micrometer alignment onto diverse photonic integration platforms. This review paper presents recent developments in the micro-transfer-enabled integration of light sources across four representative categories of devices and materials: microdisk and microring cavity lasers, photonic crystal nanobeam lasers, semiconductor nanowire lasers and LEDs, and quantum light sources based on semiconductor quantum dots and localized emitters in two-dimensional materials. For each category of light source integration, we analyze the application of micro-transfer-printing in relation to the overall integration configuration, the desired optical properties, device performance optimization, and resolution of challenges and limitations encountered in previous methodologies. Collectively, these demonstrations position PDMS-assisted micro-transfer-printing not merely as a fabrication technique but as an innovative integration paradigm that connects diverse material systems and device architectures.
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).
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.
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.
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.
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.
Analytical multilayers designed under quarter-wave conditions, such as antireflective coatings and distributed Bragg reflectors, generally perform effectively within narrow spectral bands but often face challenges in meeting multispectral demands. In contrast, machine learning (ML)-driven inverse design enables exploration of vast parameter spaces to realize tailored spectral responses across multiple bands. However, whether ML-optimized multilayers can outperform analytical designs under identical material and thickness constraints often remains an open question. Here, we experimentally validate the superiority of ML-driven design through a metal/dielectric multilayer cooling-window coating that simultaneously requires high average visible transmittance (AVT) and high average near-infrared reflectance (ANR). By integrating a factorization machine with simulated annealing, we discovered optimized aperiodic ZnS/Ag multilayers and benchmarked them against periodic hyperbolic metamaterial (HMM) counterparts. Under a 156 nm thickness constraint (equivalent to two ZnS/Ag pairs in a HMM), the ML design achieved 0.57 AVT and 0.98 ANR, surpassing the HMM reference (0.49 AVT, 0.83 ANR). With an extended thickness of 300 nm, the ML-optimized coating further improved to 0.79 AVT by suppressing Fabry-Perot resonances while maintaining high ANR (0.97). Furthermore, the ML-driven multilayers exhibited tunable transmitted colors spanning the full visible gamut, whereas the HMM counterparts were restricted to specific hues. Both ML and HMM designs were fabricated on glass, and measured spectra confirmed the superior optical and thermal performance of the ML approach. These findings establish ML-driven inverse design as a powerful route to ultrathin, manufacturable, and color-tunable cooling-window coatings that can contribute to urban energy savings.
Twisted layers of α-MoO3 support phonon polaritons whose propagation can be adjusted by the twist angle, a concept known as 'twistoptics'. Although emergent in the field of nano-optics, the application to heat transfer has lagged behind, particularly regarding near-field radiative heat transfer (NFRHT), which is important for thermal management in nanodevices and remains insufficiently explored. Here, we report the role of twistoptics in NFRHT, demonstrating that the heat flux between two separated twisted α-MoO3 bilayers can be monotonically increased by simply increasing the twist angle. Interestingly, this modulation is explained by the emergence of topological transitions from open (hyperbolic) to closed (elliptical) polaritonic dispersions. This phenomenon is further demonstrated by considering α-MoO3 gapped trilayers, which show greater flexibility in regulating the NFRHT due to the emergence of a wider variety of topological transitions. Based on these findings, we propose an experimental scenario where the NFRHT between a nanoparticle and a closely spaced twisted α-MoO3 bilayer can be modulated by a factor of 3 by simply adjusting the twist angle. This work provides theoretical guidance for the modulation of NFRHT using twistoptics, making an important step toward the development of twisted thermotics.
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.
Spin-orbit interaction (SOI) of tightly focused light in optical tweezers underpins diverse optomechanical applications and the interconversion of spin and orbital angular momentum. Here, we demonstrate that the transfer of the spin angular momentum of a tightly focused circularly polarized beam to an on-axis birefringent particle can indirectly generate spin in an adjacent particle, leading to exotic rotational motion reminiscent of planetary trajectories. We demonstrate simultaneous rotation and revolution of birefringent liquid crystal (LC) particles by harvesting SOI, such that its two principal governing mechanisms-the momentum-dependent Pancharatnam-Berry (PB) phase and the anisotropy-induced PB phase-become coupled. In our experiments, a centrally trapped LC particle in spherically aberrated optical tweezers spins under circularly polarized illumination, generating spin-induced microfluidic flows that drive surrounding off-axis LC particles into orbital motion. Simultaneously, interaction of the input helicity with the centrally trapped particle induces spin-to-spin conversion through extrinsic SOI. The helicity thereby generated indirectly then couples to the orbiting particles, imparting an additional rotation whose direction is determined by the birefringence of the central particle. A Mueller matrix model that incorporates tight focusing and scattering quantitatively explains these observations. Thus, SOI coupled with microfluidic effects establishes exotic rotational optomechanics and microswitch applications.
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.
Dark states of photoluminescence (PL) intermittency in colloidal quantum dots (QDs) interrupt PL emission and significantly reduce emission intensity, severely hindering QD applications. However, the origin of dark states remains ambiguous due to their extremely low intensity, which impedes the development of effective suppression strategies. In this study, we use plasmonic gold nanoparticles to significantly increase the radiative rate of excitons, and thereby enhancing the dark-state PL intensity. Calculations of radiative rate scaling based on the dark-state PL intensity and lifetime reveal that the dark states originate from band-edge carrier trapping by collectively activated nonradiative multiple recombination centers (MRCs). Transition states that accompany the dark states are frequently observed in PL trajectories, revealing the presence of a positive feedback mechanism for the activation and deactivation of nonradiative MRCs induced by the phonon kick effect. We perform a Monte Carlo simulation to model the dark and transition states and quantify the nonradiative rates involved. Understanding the origin of dark states can contribute to their suppression, optimization of synthesis, and improvement of performance in QD-based applications.
Vortex beams, known for carrying orbital angular momentum (OAM), demonstrate significant potential across LiDAR, laser communications, high-precision metrology, imaging, and quantum information. Generating vortex beam on demand is the basis and crucial for above implementations. Recently, solid-state vortex laser in eye-safe band have attracted considerable attention and been regarded as one of ideal sources for vortex beam generation, because of its advantages in high mode purity, mode selectivity, high output power, and locating in atmosphere window. In this perspective, we summarize the schemes of solid-state vortex lasers in eye-safe band, survey their potential in multi-functional LiDAR systems, and discuss prospects for future development.