Nature Photonics最新文献

Understanding the impact of spatial heterogeneity on the behaviour of two-dimensional materials represents one of the grand challenges in applying these materials in optoelectronics and quantum information science. For transition metal dichalcogenide heterostructures in particular, direct access to heterogeneities in the dark-exciton landscape with nanometre spatial and ultrafast time resolution is highly desired but remains largely elusive. Here we report how ultrafast dark-field momentum microscopy can spatio-temporally resolve dark-exciton formation dynamics in a twisted WSe₂/MoS₂ heterostructure with a time resolution of 55 fs and a spatial resolution of 480 nm. This enables us to directly map spatial heterogeneity in the electronic and excitonic structure, and to correlate this with the dark-exciton formation and relaxation dynamics. The advantage of the simultaneous ultrafast nanoscale dark-field momentum microscopy and spectroscopy reported here is that it enables spatio-temporal imaging of the photoemission spectral function that carries energy- and momentum-resolved information on the single-particle band structure, many-body interactions and correlation phenomena.

Optically bistable materials respond to a single input with two possible optical outputs, contingent on excitation history. Such materials would be ideal for optical switching and memory, but the limited understanding of intrinsic optical bistability (IOB) prevents the development of nanoscale IOB materials suitable for devices. Here we demonstrate IOB in Nd³⁺-doped KPb₂Cl₅ avalanching nanoparticles, which switch with high contrast between luminescent and non-luminescent states, with hysteresis characteristic of bistability. We elucidate a non-thermal mechanism in which IOB originates from suppressed non-radiative relaxation in Nd³⁺ ions and from the positive feedback of photon avalanching, resulting in extreme, >200th-order optical nonlinearities. The modulation of laser pulsing tunes the hysteresis widths, and dual-laser excitation enables transistor-like optical switching. This control over nanoscale IOB establishes avalanching nanoparticles for photonic devices in which light is used to manipulate light.

Integrated photonic chips hold substantial potential in optical communications, computing, light detection and ranging, sensing, and imaging, offering exceptional data throughput and low power consumption. A key objective is to build a monolithic on-chip photonic system that integrates light sources, processors and photodetectors on a single chip. However, this remains challenging due to limitations in materials engineering, chip integration techniques and design methods. Perovskites offer simple fabrication, tolerance to lattice mismatch, flexible bandgap tunability and low cost, making them promising for hetero-integration with silicon photonics. Here we propose and experimentally realize a near-infrared monolithic on-chip photonic system based on a perovskite/silicon nitride photonic platform, developing nano-hetero-integration technology to integrate efficient light-emitting diodes, high-performance processors and sensitive photodetectors. Photonic neural networks are implemented to perform photonic simulations and computer vision tasks. Our network efficiently predicts the topological invariant in a two-dimensional disordered Su–Schrieffer–Heeger model and simulates nonlinear topological models with an average fidelity of 87%. In addition, we achieve a test accuracy of over 85% in edge detection and 56% on the CIFAR-10 dataset using a scaled-up architecture. This work addresses the challenge of integrating diverse nanophotonic components on a chip, offering a promising solution for chip-integrated multifunctional photonic information processing.

Leveraging the entire space of complex dielectric permittivity, non-Hermitian photonics has fundamentally altered wave propagation with complex optical potentials and has ushered in a host of new photonic applications. Through parity–time symmetry and its breaking—a delicate interplay between gain and loss—even the interaction between just two entities becomes counter-intuitive and intriguing. Here we realize, through hybrid III–V/Si integration, a scalable non-Hermitian switching network on a two-layer integrated photonic chip. Our platform is a hybrid, with a bottom silicon layer and a top InGaAsP layer that provides optical gain. By tuning the gain level in the top layer, vertically coupled waveguides operate below or above the exceptional point, where light is switched across two layers, among different input–output ports. For a single switching unit, the switching dynamics are ultrafast, on the order of 100 ps. In a large switching network, non-blocking and other diverse connectivities are established in single-wavelength and wavelength-selective switching, with high extinction ratios. Our approach adds scalable non-Hermitian switching to photonic design toolkits to simultaneously boost the switching time and bandwidth density to cutting-edge levels, therefore paving the way for compact and ultrafast monolithic integrated silicon photonics in next-generation optical information networks.

Applications of waves in communications, information processing and sensing need a clear understanding of how many strongly coupled channels or degrees of freedom exist in and out of volumes of space and how the coupling falls off for larger numbers. Numerical results are possible, and some heuristics exist, but there has been no simple physical picture and explanation for arbitrary volumes. By considering waves from a bounding spherical volume, we show a clear onset of a tunnelling escape of waves that both defines a limiting number of well-coupled channels for any volume and explains the subsequent rapid fall-off of coupling strengths. The approach works over all size scales, from nanophotonics and small radiofrequency antennas up to imaging optics. It gives a unified view from the multipole expansions common for antennas and small objects to the limiting plane and evanescent waves of large optics, showing that all such waves can escape to propagation to some degree, by tunnelling if necessary, and gives a precise diffraction limit.