Nanophotonics (Berlin, Germany)最新文献

We re-examine real-time holography for all-optical structuring of light and optical computation using a contemporary material: a subwavelength-thick, spatially unstructured film of indium tin oxide (ITO). When excited by spatially structured light at epsilon-near-zero frequencies, the film acts as an efficient and reconfigurable diffractive optical platform for all-optical modulation of light such as spatial structuring and optical computations. We demonstrate a few percent of absolute diffraction efficiency over greater than 300-nm-bandwidth around telecom wavelengths using a film four orders of magnitude thinner than and up to six orders of magnitude faster than standard holographic materials. Our findings highlight the potential of using epsilon-near-zero-based nanostructures for efficient modulation of spatially structured light and rapid prototyping without complex nanofabrication processes.

Recent advancements of anisotropic phonon polaritons (PhPs) in low-dimensional van der Waals (vdW) materials enable efficient control of long-wavelength light at nanoscale with ultrahigh confinement and low loss. The theoretical analysis based on the two-dimensional (2D) surface conductivity model has been widely exploited, for its simplicity, to understand fundamental phenomena at the surface of vdW slabs, which, however, neglects the intrinsic higher-order waveguide modes excited therein. Here, we report a generalized surface conductivity model which can allow us to include all waveguide modes, by taking into account the out-of-plane dimensions. In doing so, we can separate and examine each individual waveguide mode in vdW slabs with 2D models, and to further clarify the contribution of each polaritonic mode in near-field light matter interactions. As a concrete example, we examine the enhancement of photonic local density of states by PhPs in the α-phase molybdenum trioxide and hexagonal boron nitride plates and show that higher-order waveguide PhPs, instead of fundamental ones, surprisingly dominate the enhancement of light-matter interactions close to the surface. Our findings provide fundamentally relevant insights into anisotropic polaritons in vdW materials and beyond, important in near-field energy and information transport and other nanophotonic phenomena.

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.

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.

Optical metasurfaces are widely studied due to their unprecedented wavefront modulation capabilities for multiple polarization channels. Current studies predominantly focus on complete polarization conversion. Recent progress indicates that the phases of quadruplex polarization channels can be independently modulated under incomplete polarization conversion conditions. However, these four-channel phase modulation operations are limited to circular or linear polarization states and neglect amplitude modulation. Here, a strategy is proposed to achieve four-channel phase modulation and flexible energy distribution of arbitrary orthogonal polarization states under incomplete polarization conversion conditions. Wavefront modulations for quadruplex channels of arbitrary orthogonal polarization states (circular, linear, elliptical, and first-order cylindrically vectorial), such as orbital angular momentum manipulation, Bessel beam generation, deflection, and holography, are numerically demonstrated based on this strategy. Furthermore, the energy distribution of the quadruplex polarization channels is achieved by varying the polarization conversion efficiency. These operations are implemented through all-dielectric free-standing bilayer metasurfaces. The proposed design strategy extends the application of metasurfaces in multichannel optical field modulation.

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.

Broadband directional thermal emitters have attracted significant attention due to their potential applications in infrared camouflage and radiative cooling. However, existing broadband directional thermal emission (BDTE) multilayer structures rely heavily on the Berreman modes of epsilon-near-zero (ENZ) materials, usually requiring a substantial number of stacked ENZ thin films for broader spectral coverage. Moreover, the lack of optimized thicknesses fails to achieve the optimal figure of merit (FOM) of BDTE. Here, we have realized a high-FOM BDTE structure with a reduced number of ENZ layers based on Bayesian optimization. By coupling epsilon-near-pole (ENP) resonance with the Brewster effect of the dielectric spacer, we extend the BDTE bandwidth by 2 μm (from 7.9-12 to 7.9-14 μm). The optimized structure shows unprecedented performance, achieving an average directional emissivity of 0.94 and an FOM of 8.087, which are also validated by experimental measurements. Notably, by integrating our emitter with low-emissivity covers, we develop a series of patterned devices for infrared information encryption and deception applications, which exhibit angle-dependent distinct, even contradictory, infrared information. This work not only provides theoretical guidance for the design and optimization of BDTE structures but also paves the way for their applications in infrared information technologies.

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.

Manipulating propagating waves (PWs) and surface waves (SWs) in desired manners is important in photonics, but controlling these two electromagnetic modes usually requires separate devices, which is unfavorable for integration optics applications. Recently, although metasurfaces capable of controlling both PWs and SWs have been proposed, they typically rely on dynamically varying the helicities of incident circularly polarized (CP) light, causing complexities in practical applications. In this work, we propose an alternative scheme for designing metasurfaces encoded with both resonance and geometric phases that can simultaneously control PWs and SWs through the co- and cross-polarized output channels under the excitation of a CP wave with a particular helicity. We experimentally prove this concept by realizing two microwave metadevices that can convert normally incident beams with left circular polarization (LCP) into PWs and SWs with predetermined wavefronts. Additionally, we numerically demonstrate how to design metadevices with predetermined energy distributions within these two functional output channels. Our work paves the road to tailor both far- and near-field electromagnetic waves using a single ultra-compact platform, which can find many applications in integrated optics.