The authors comment on a recent significant advancement in developing a chiral sensor that is both sensitive and robust.

Optical vortices, characterized by their infinite orthogonal eigenmodes—such as orbital angular momentum (OAM) and cylindrical vector beam (CVB) modes—offer unprecedented opportunities for advancing optical communication systems. The core components of these systems—mode (de)modulation, mode processing, and mode transmission—are fundamental to the construction and networking of OAM/CVB mode-based communication networks. They significantly influence signal encoding, enhance channel capacity, and facilitate signal interconnection and transmission. We explore the historical development and recent advancements in optical vortex-based communication systems from these three critical perspectives. We systematically summarize the normative definitions and research progress related to key concepts such as mode multiplexing and routing. We also demonstrate the performance of these systems in terms of communication capacity, bit error rate, and more. Furthermore, we examine the substantial challenges and future prospects in this field, with the aim of offering cutting-edge insights that will facilitate the advancement and practical implementation of optical communication networks leveraging optical vortex modes.

Spatial photonic Ising machines (SPIMs) are promising computation devices that can be used to find the ground states of different spin Hamiltonians and solve large-scale optimization problems. The photonic architecture leverages the matrix multiplexing ability of light to accelerate the computing of spin Hamiltonian via free space light transform. However, the intrinsic long-range nature of spatial light only allows for uncontrolled all-to-all spin interaction. We explore the ability to establish arbitrary spin Hamiltonian by modulating the momentum of light. Arbitrary displacement-dependent spin interactions can be computed from different momenta of light, formulating as a generalized Plancherel theorem, which allows us to implement a SPIM with a minimal optical operation (that is, a single Fourier transform) to obtain the Hamiltonian of customized spin interaction. Experimentally, we unveil the exotic magnetic phase diagram of the generalized J1-J2-J3 model, shedding light on the ab initio magnetic states of iron chalcogenides. Moreover, we observe Berezinskii-Kosterlitz-Thouless dynamics by implementing an XY model. We open an avenue to controlling arbitrary spin interaction from the momentum space of light, offering a promising method for on-demand spin model simulation with a simple spatial light platform.

Twisted optical fibers are a promising platform for manipulating circularly polarized light and orbital angular momentum beams for applications such as nonlinear frequency conversion, optical communication, or chiral sensing. However, integration into chip-scale technology is challenging because twisted fibers are incompatible with planar photonics and the achieved twist rates are limited. Here, we address these challenges by introducing the concept of 3D-nanoprinted on-chip twisted hollow-core light cages. We show theoretically and experimentally that the geometrical twisting of light cages forces the fundamental core mode of a given handedness to couple with selected higher-order core modes, resulting in strong circular dichroism (CD). These chiral resonances result from the angular momentum harmonics of the fundamental mode, allowing us to predict their spectral locations and the occurrence of circular birefringence. Twisted light cages enable very high twist rates and CD, exceeding those of twisted hollow-core fibers by more than two orders of magnitude (twist period, 90 μm; CD, 0.8 dB / mm). Moreover, the unique cage design provides lateral access to the central core region, enabling future applications in chiral spectroscopy. Therefore, the presented concept opens a path for translating twisted fiber research to on-chip technology, resulting in a new platform for integrated chiral photonics.

Optical neural networks have emerged as feasible alternatives to their electronic counterparts, offering significant benefits such as low power consumption, low latency, and high parallelism. However, the realization of ultra-compact nonlinear deep neural networks and multi-thread processing remain crucial challenges for optical computing. We present a monolithically integrated all-optical nonlinear diffractive deep neural network (AON-D2NN) chip for the first time. The all-optical nonlinear activation function is implemented using germanium microstructures, which provide low loss and are compatible with the standard silicon photonics fabrication process. Assisted by the germanium activation function, the classification accuracy is improved by 9.1% for four-classification tasks. In addition, the chip’s reconfigurability enables multi-task learning in situ via an innovative cross-training algorithm, yielding two task-specific inference results with accuracies of 95% and 96%, respectively. Furthermore, leveraging the wavelength-dependent response of the chip, the multi-thread nonlinear optical neural network is implemented for the first time, capable of handling two different tasks in parallel. The proposed AON-D2NN contains three hidden layers with a footprint of only 0.73 mm2. It can achieve ultra-low latency (172 ps), paving the path for realizing high-performance optical neural networks.

Recent progress in direct photodetection of light orbital angular momentum (OAM) based on the orbital photogalvanic effect (OPGE) provides an effective way for on-chip direct electric readout of orbital angular momentum, as well as large-scale integration focal-plane array devices. However, the recognition of OAM order from photocurrent response requires the extraction of circular polarization-dependent response. To date, the operation speed of such a detector is currently at the minute level and is limited by slow mechanical polarization modulation and low OAM recognition capability. We demonstrate that the operation speed can be greatly improved via an electrical polarization modulation strategy with a photoelastic modulator (PEM) accompanied by a phase-locked readout approach with a lock-in amplifier. We demonstrate an operation speed of up to kilohertz level with this new technology in the mid-infrared region (4 μm) on an OAM detector using multilayer graphene as photosensitive material. In principle, with a new modulation and readout scheme, we can potentially increase the operation speed to megahertz with a PEM that operates at a state-of-the-art speed. Our work paves the way toward high-speed operation of direct OAM detection devices based on the OPGE effect and pushes such technology to a more practical stage for focal plane array applications.

Flatbands are of significant interest due to their potential for strong energy confinement and their ability to facilitate strongly correlated physics such as unconventional superconductivity and fractional quantum Hall states. When topology is incorporated into flatband systems, it further enhances flatband mode robustness against perturbations. We present the first realization of doubly degenerate topological flatbands of edge states in chiral-symmetric strained graphene. The flatband degeneracy stems from the merging of Dirac points, achieved by tuning the coupling ratios in a honeycomb lattice with newly discovered twig boundary conditions. The topology of these modes is characterized by the nontrivial winding number, which ensures their robustness against disorder. Experimentally, two types of topological edge states are observed in a strained photonic graphene lattice, consistent with numerical simulations. Moreover, the degeneracy of the topological flatbands doubles the density of states for zero-energy modes, facilitating the formation of compact edge states and providing greater control over edge states and light confinement. Our findings underscore the interplay among lattice geometry, symmetry, and topology in shaping doubly degenerate topological flatbands. This work opens new possibilities for advancements in correlated effects, nonlinear optical phenomena, and efficient energy transfer in materials science, photonic crystals, and quantum devices.

Metalenses have exhibited significant promise across various applications due to their ultrathin, lightweight, and flat architecture, which allows for integration with microelectronic devices. However, their overall imaging capabilities, particularly in microscopy, are hindered by substantial off-axis aberrations that limit both the field of view (FOV) and resolution. To address these issues, we introduce a meta-microscope that utilizes a metalens doublet incorporated with annular illumination, enabling wide FOV and high-resolution imaging in a compact design. The metalens-doublet effectively mitigates off-axis aberrations, whereas annular illumination boosts resolution. To validate this design, we constructed and tested the meta-microscope system, attaining a record resolution of 310 nm (for metalens image) with a 150 μm FOV at 470 nm wavelength. Moreover, by utilizing the integration of metasurface, we implemented a compact prototype achieving an impressive 1-mm FOV with a resolution of 620 nm. Our experimental results demonstrate high-quality microscopic bio-images that are comparable to those obtained from traditional microscopes within a compact prototype, highlighting its potential applications in portable and convenient settings, such as biomedical imaging, mobile monitoring, and outdoor research.

Lightweight augmented reality (AR) eyeglasses have been increasingly integrated into human daily life for navigation, education, training, healthcare, digital twins, maintenance, and entertainment, just to name a few. To facilitate an all-day comfortable wearing, AR glasses must have a small form factor and be lightweight while keeping a sufficiently high ambient contrast ratio, especially under outdoor diffusive sunlight conditions and low power consumption to sustain a long battery operation life. These demanding requirements pose significant challenges for present AR light engines due to the relatively low efficiency of the optical combiners. We focus on analyzing the power consumption of five commonly employed microdisplay light engines for AR glasses, including micro-LEDs, OLEDs, liquid-crystal-on-silicon, laser beam scanning, and digital light processing. Their perspectives and challenges are also discussed. Finally, adding a segmented smart dimmer in front of the AR glasses helps improve the ambient contrast ratio and reduce the power consumption significantly.

The femtosecond laser direct writing technique is a highly precise processing method that enables the rapid fabrication of three-dimensional (3D) micro- and nanoscale photonic structures in transparent materials. By focusing ultrashort laser pulses into transparent optical materials, such as crystals and glasses, it is possible to efficiently modify specific optical properties, including refractive indices and ferroelectric domains, at the laser focus. By carefully designing and optimizing the movement trajectory of the femtosecond laser, one can achieve periodic modulation of the optical features of these materials in 3D space. The resulting changes in material properties are closely linked to both the processing parameters of the femtosecond laser and the types of materials used. Through ongoing optimization of these parameters, desired periodic photonic structures can be created in specific transparent optical materials, leading to the development of 3D nonlinear photonic crystals (NPCs) and 3D waveguide arrays. Femtosecond laser direct writing breaks through the limitations of traditional techniques to fabricate 3D NPCs [e.g., 3D lithium niobate (LiNbO3) NPCs] and complex waveguide arrays (e.g., 3D helical waveguide arrays), realizing a paradigm shift in the fabrication of complex periodic photonic structures. To date, femtosecond-laser-written 3D NPCs and waveguide arrays have found extensive applications in integrated photonics, nonlinear optics, quantum optics, and topological photonics. We highlight recent advancements in femtosecond-laser-written 3D NPCs and waveguide arrays, such as pivotal breakthroughs in the fabrication of nanoscale-resolution 3D NPCs in LiNbO3. Finally, several potential research directions, such as the formation mechanism of domain wall and inducing millimeter-scale domain inversion with femtosecond Bessel beam, have been proposed at the end of this article.

Lead halide perovskites have started a new era for solar cells. However, the toxicity of lead poses a challenge for their practical applications. Replacing lead with tin provides a feasible way to reduce the toxicity of lead perovskites and can further promote the applications of perovskites. Due to their reduced toxicity with advantageous optical and electronic properties compared to their lead counterparts, tin (II) perovskites (TiPes) have attracted significant interest in recent years, not only for pursuing high-performance solar cells but also in other application fields. We aim to provide a comprehensive overview of recent advances in TiPes, covering fundamental crystal structure, optoelectronic properties, fabrication methods, and applications. A detailed comparison with lead perovskites is included, emphasizing TiPes’ unique strengths while presenting their application challenges. Finally, potential solutions to the challenges are proposed, along with a vision for their future development and potential.

The rapid advancement of renewable energy technologies is essential for combating global climate change and achieving energy sustainability. Among the various renewable sources, solar energy stands out, with silicon playing a pivotal role in solar energy conversion. However, traditional silicon-based devices often face challenges due to high surface reflectance, which limits their efficiency. The emergence of black silicon (b-Si) offers a transformative solution, thanks to its micro- and nanoscale structures that provide ultra-low reflectivity and enhanced light absorption. This makes b-Si an ideal candidate for improving solar energy devices. Beyond solar energy applications, b-Si has drawn notable interest in photonics, including applications in photodetectors, surface-enhanced Raman scattering, and imaging. This review explores b-Si comprehensively, discussing its fabrication processes, distinctive properties, and contributions to both solar energy conversion and photonic technologies. Key topics include its roles in solar cells, photoelectrochemical systems, solar thermal energy conversion, and advanced photonic devices. Furthermore, the review addresses the challenges and future directions for optimizing b-Si to facilitate its practical deployment across a range of energy and photonic applications.

Metasurface modeling, designs, and applications using computational approaches are by now well established as an essential pillar in photonics, physics, and materials science. The past years have witnessed tremendous advances in methodologies and technologies to unearth the intricate light–matter interaction and promote adaptive metadevices. They have pushed the studies of metasurfaces from early passive, reconfigurable modalities to the next generation of intelligent metasurfaces. In this review, we elaborate general architecture for intelligent metasurfaces, constructed by the algorithm layer, tunable metasurface layer, and application layer. We first discuss a variety of deep learning models, ranging from the fundamental neural networks inspired by computer science to sophisticated algorithms embedded with physical specialty, highlighting their potential in the forward prediction, inverse design, and spectral correlation of metasurfaces. We then discuss adaptive metadevices in the main applications of invisibility cloaks, smart vision, intelligent sensing, and wireless communication. Finally, we pinpoint current challenges and future perspectives to embrace the coming era of intelligent metasurfaces.

Photonic devices that exhibit both sensitivity and robustness have long been sought; yet, these characteristics are thought to be mutually exclusive; through sensitivity, a sensor responds to external stimuli, whereas robustness embodies the inherent ability of a device to withstand weathering by these same stimuli. This challenge stems from the inherent contradiction between robustness and sensitivity in wave dynamics, which require the coexistence of noise-immune sensitive states and modulation-sensitive transitions between these states. We report and experimentally demonstrate a subwavelength phase singularity in a chiral medium that is resilient to fabrication imperfections and disorder while remaining highly responsive to external stimuli. The combination of subwavelength light confinement and its robustness lays the foundation for the development of hitherto unexplored chip-scale photonics devices, enabling a simultaneous development of high-sensitivity and robust devices in both quantum and classical realms.

Hyperbolic materials are highly anisotropic optical media that provide valuable assistance in emission engineering, nanoscale light focusing, and scattering enhancement. Recently discovered organic hyperbolic materials (OHMs) with exceptional biocompatibility and tunability offer promising prospects as next-generation optical media for nanoscopy, enabling superresolution bioimaging capabilities. Nonetheless, an OHM is still less accessible to many researchers because of its rarity and narrow operating wavelength range. Here, we employ first-principles calculations to expand the number of known OHMs, including conjugated polymers with multiple assembly units. Through the systematic investigation of structural and optical properties of the target copolymers, we discover extraordinary multiband hyperbolic dispersions from candidate OHMs. This approach provides a new perspective on the molecular-scale design of broadband, low-loss OHMs. It aids in identifying potential hyperbolic material candidates applicable to optical engineering and super-resolution bioimaging, offering new insights into nanoscale light–matter interactions.

Landau–Zener (LZ) tunneling, i.e., the nonadiabatic level transition under strong parameter driving, is a fundamental concept in modern quantum mechanics. With the advent of non-Hermitian physics, research interest has been paid to the LZ tunneling involving level dissipations. However, experimental demonstrations of such an interesting non-Hermitian LZ problem remain yet elusive. By harnessing a synthetic temporal lattice using a fiber-loop circuit, we report on the first real-time measurement of non-Hermitian LZ tunneling in a dissipative two-band lattice model. An innovative approach based on mode interference is developed to measure the transient band occupancies, providing a powerful tool to explore the non-Hermitian LZ tunneling dynamics in non-orthogonal eigenmodes. We find that the loss does not change the final LZ tunneling probability but can highly affect the tunneling process by modifying the typical band occupancies oscillation behaviors. We initiate exploring intriguing LZ physics and measurements beyond the standard Hermitian paradigm, with potential applications in coherent quantum control and quantum technologies.

Super-resolution microscopy techniques have revolutionized biological imaging by breaking the optical diffraction limit, yet most methods rely on fluorescent labels that provide limited chemical information. Although vibrational imaging based on Raman and infrared (IR) spectroscopy offers intrinsic molecular contrast, achieving both high spatial resolution and high chemical specificity remains challenging due to weak signal levels. We demonstrate structured illumination mid-infrared photothermal microscopy (SIMIP) as an emerging imaging platform that provides chemical bond selectivity and high-speed, widefield detection beyond the diffraction limit. By modulating fluorescence quantum yield through vibrational infrared absorption, SIMIP enables both nanoscale spatial resolution and high-fidelity IR spectral acquisition. The synergy of enhanced resolution and chemical specificity positions SIMIP as a versatile tool for studying complex biological systems and advanced materials, offering new opportunities across biomedicine and materials science.

Although predicting light scattering by homogeneous spherical particles is a relatively straightforward problem that can be solved analytically, manipulating and studying the scattering behavior of non-spherical particles is a more challenging and time-consuming task, with a plethora of applications ranging from optical manipulation to wavefront engineering, and nonlinear harmonic generation. Recently, physics-driven machine learning (ML) has proven to be instrumental in addressing this challenge. However, most studies on Mie-tronics that leverage ML for optimization and design have been performed and validated through numerical approaches. Here, we report an experimental validation of an ML-based design method that significantly accelerates the development of all-dielectric complex-shaped meta-atoms supporting specified Mie-type resonances at the desired wavelength, circumventing the conventional time-consuming approaches. We used ML to design isolated meta-atoms with specific electric and magnetic responses, verified them within the quasi-normal mode expansion framework, and explored the effects of the substrate and periodic arrangements of such meta-atoms. Finally, we proposed implementing the designed meta-atoms to generate a third harmonic within the vacuum ultraviolet spectrum. Because the implemented method allowed for the swift transition from design to fabrication, the optimized meta-atoms were fabricated, and their corresponding scattering spectra were measured.