理学最新文献

In photonic structures, bound states in the continuum (BICs) have recently attracted huge interest in both fundamental and applied research. Quasi-BIC leaky modes resulting from in-plane symmetry breaking in metasurfaces are particularly relevant to applications, due to their high quality factor, which scales as the squared inverse of the asymmetry parameter. Here, we theoretically propose an innovative approach to switch on quasi-BICs on sub-picosecond timescales via optically induced symmetry breaking in semiconductor metasurfaces. The desired effect is granted by exploiting the spatial inhomogeneities in the distribution of photo-excited hot carriers at the single meta-atom nanometric scale. In our simulations, the quasi-BIC state manifests itself as an ultra-sharp dip in transmission, emerging upon pump arrival, and disappearing completely within the carriers’ diffusion timescale. Our strategy allows to envision reconfigurable platforms with switchable high-Q resonances, with ultrafast recovery beyond the limits of carrier relaxation, typical of previous approaches.

Kerr soliton microcombs have the potential to disrupt a variety of applications such as ultra-high-speed optical communications, ultra-fast distance measurements, massively parallel light detection and ranging (LiDAR) or high-resolution optical spectroscopy. Similarly, ultra-broadband photonic-electronic signal processing could also benefit from chip-scale frequency comb sources that offer wideband optical emission along with ultra-low phase noise and timing jitter. However, while photonic analogue-to-digital converters (ADC) based on femtosecond lasers have been shown to overcome the jitter-related limitations of electronic oscillators, the potential of Kerr combs in photonic-electronic signal processing remains to be explored. In this work, we demonstrate a microcomb-based photonic-electronic ADC that combines a high-speed electro-optic modulator with a Kerr comb for spectrally sliced coherent detection of the generated optical waveform. The system offers a record-high acquisition bandwidth of 320 GHz, corresponding to an effective sampling rate of at least 640 GSa/s. In a proof-of-concept experiment, we demonstrate the viability of the concept by acquiring a broadband analogue data signal comprising different channels with centre frequencies between 24 GHz and 264 GHz, offering bit error ratios (BER) below widely used forward-error-correction (FEC) thresholds. To the best of our knowledge, this is the first demonstration of a microcomb-based ADC, leading to the largest acquisition bandwidth demonstrated for any ADC so far.

Graphene’s unique photothermoelectric (PTE) effect, combined with its compatibility for on-chip fabrication, promises its development in chip-integrated photodetectors with ultralow dark-current and ultrafast speed. Previous designs of on-chip graphene photodetectors required external electrical biases or gate voltages to separate photocarriers, leading to increased power consumption and complex circuitry. Here, we demonstrate a nonvolatile graphene p–i–n homojunction constructed on a silicon photonic crystal waveguide, which facilitates PTE-based photodetection without the need for electrical bias or gate voltages. By designing an air-slotted photonic crystal waveguide as two individual silicon back gates and employing ferroelectric dielectrics with remnant polarization fields, the nonvolatile p–i–n homojunction with a clear gradient of Seebeck coefficient is electrically configured. Hot carriers in the graphene channel generated from the absorption of waveguide evanescent field are separated by the nonvolatile p–i–n homojunction effectively to yield considerable photocurrents. With zero-bias and zero-gate voltage, the nonvolatile graphene p–i–n homojunction photodetector integrated on the optical waveguide exhibits high and flat responsivity of 193 mA W⁻¹ over the broadband wavelength range of 1560–1630 nm and an ultrafast dynamics bandwidth of 17 GHz measured in the limits of our instruments. With the high-performance on-chip photodetection, the nonvolatile graphene homojunction directly constructed on silicon photonic circuits promises the extended on-chip functions of the optoelectronic synapse, in-memory sensing and computing, and neuromorphic computing.

Fourier ptychography (FP) offers both wide field-of-view and high-resolution holographic imaging, making it valuable for applications ranging from microscopy and X-ray imaging to remote sensing. However, its practical implementation remains challenging due to the requirement for precise numerical forward models that accurately represent real-world imaging systems. This sensitivity to model-reality mismatches makes FP vulnerable to physical uncertainties, including misalignment, optical element aberrations, and data quality limitations. Conventional approaches address these challenges through separate methods: manual calibration or digital correction for misalignment; pupil or probe reconstruction to mitigate aberrations; or data quality enhancement through exposure adjustments or high dynamic range (HDR) techniques. Critically, these methods cannot simultaneously address the interconnected uncertainties that collectively degrade imaging performance. We introduce Uncertainty-Aware FP (UA-FP), a comprehensive framework that simultaneously addresses multiple system uncertainties without requiring complex calibration and data collection procedures. Our approach develops a fully differentiable forward imaging model that incorporates deterministic uncertainties (misalignment and optical aberrations) as optimizable parameters, while leveraging differentiable optimization with domain-specific priors to address stochastic uncertainties (noise and data quality limitations). Experimental results demonstrate that UA-FP achieves superior reconstruction quality under challenging conditions. The method maintains robust performance with reduced sub-spectrum overlap requirements and retains high-quality reconstructions even with low bit sensor data. Beyond improving image reconstruction, our approach enhances system reconfigurability and extends FP’s capabilities as a measurement tool suitable for operation in environments where precise alignment and calibration are impractical.

The generation of tunably focused light at remote locations is a critical photonic functionality for a wide range of applications. Here, we present a novel concept in the emerging field of Metafibers that achieves, for the first time, fast, alignment-free, fiber-integrated spatial focus control in a monolithic arrangement. This is enabled by 3D nanoprinted intensity-sensitive phase-only on-fiber holograms, which establish a direct correlation between the intensity distribution in the hologram plane and the focus position. Precise adjustment to the relative power between the modes of a dual-core fiber generates a power-controlled interference pattern within the hologram, enabling controlled and dynamic focus shifts. This study addresses all relevant aspects, including computational optimization, advanced 3D nanoprinting, and tailored fiber fabrication. Experimental results supported by simulations validate the feasibility and efficiency of this monolithic Metafiber platform, which enables fast focus modulation and has transformative potential in optical manipulation, high-speed laser micromachining, telecommunications, and minimally invasive surgery.

Owing to its unique ability to capture volumetric tomographic information with a single light flash, optoacoustic (OA) tomography has recently demonstrated ultrafast imaging speeds ultimately limited by the ultrasound time-of-flight. The method’s scalability and the achievable spatial resolution are yet limited by the narrow bandwidth of piezo-composite arrays currently employed for OA signal detection. Here we report on the first implementation of high-density spherical array technology based on flexible polyvinylidene difluoride films featuring ultrawideband (0.3–40 MHz) sub mm² area elements, thus enabling real-time multi-scale volumetric imaging with 22–35 µm spatial resolution, superior image fidelity and over an order of magnitude signal-to-noise enhancement compared to piezo-composite equivalents. We further demonstrate five-dimensional (spectroscopic, time-resolved, volumetric) imaging capabilities by visualizing fast stimulus-evoked cerebral oxygenation changes in mice and performing real-time functional angiography of deep human micro-vasculature. The new technology thus leverages the true potential of OA for quantitative high-resolution visualization of rapid bio-dynamics across scales.

The canine gut microbiome plays a vital role in overall health and well-being by regulating various physiological functions, including digestion, immune responses, energy metabolism, and even behavior and temperament. As such, a comprehensive understanding of the diversity and functional roles of the canine gut microbiome is crucial for maintaining optimal health and well-being. In healthy dogs, the gut microbiome typically consists of a diverse array of bacterial phyla, including Firmicutes, Bacteroidetes, Actinobacteria, Fusobacteria, and Proteobacteria. These microbial communities form a complex ecosystem that interacts with the host to support canine health and homeostasis. A well-balanced microbiome, known as eubiosis, represents an optimized microbial composition that enhances host health and metabolic functions. Eubiosis is shaped by interactions between host physiology and environmental factors. However, dysbiosis, a disruption of eubiosis, can contribute to various health issues, such as weight fluctuations, metabolic disorders, and behavioral changes. Maintaining eubiosis in the canine gut microbiome requires customized management strategies that consider both physiological traits and environmental influences. In this review, we explored the structure and function of the canine gut microbiome, with particular emphasis on its role in health and the key factors that influence and support its maintenance.

Background: Tryptophan is essential for nutrition, immunity and neural activity, but cannot be synthesized endogenously. Certain natural products influence host health by modulating the gut microbiota to promote the production of tryptophan metabolites. Sanguinarine (SAN) enhances broiler immunity, however, its low bioavailability and underlying mechanisms remain unclear. This study aimed to decode the mechanisms by which sanguinarine enhances intestinal immune function in broilers.

Methods: Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was employed to identify the main metabolites of sanguinarine in the intestine. Subsequently, equal concentrations of sanguinarine and its metabolites were separately added to the diets. The effects of sanguinarine and its metabolites on the intestinal immune function of broiler chickens were evaluated using 16S rRNA gene amplicon sequencing and tryptophan metabolomics approaches.

Results: We determined that dihydrosanguinarine (DHSA) is the main metabolite of sanguinarine in the intestine. Both compounds increased average daily gain and reduced feed efficiency, thereby improving growth performance. They also enhanced ileal villus height and the villus-to-crypt (V/C) ratio while decreasing crypt depth and upregulating the mRNA expression of tight junction proteins ZO-1, occludin and claudin-1. Furthermore, both compounds promoted the proliferation of intestinal Lactobacillus species, a tryptophan-metabolizing bacterium, stimulated short-chain fatty acid production, and lowered intestinal pH. They regulated tryptophan metabolism by increasing the diversity and content of indole tryptophan metabolites, activating the aryl hydrocarbon receptor (AhR) pathway, and elevating the mRNA levels of CYP1A1, CYP1B1, SLC3A1, IDO2 and TPH1. Inflammatory cytokines IL-1β and IL-6 were inhibited, while anti-inflammatory cytokines IL-10 and IL-22, serum SIgA concentration, and intestinal MUC2 expression were increased. Notably, DHSA exhibited a more pronounced effect on enhancing immune function compared to SAN.

Conclusions: SAN is converted to DHSA in vivo, which increases its bioavailability. DHSA regulates tryptophan metabolism by activating the AhR pathway and modulating immune-related factors through changes in the gut microbiota. Notably, DHSA significantly increases the abundance of Lactobacillus, a key tryptophan-metabolizing bacterium, thereby enhancing intestinal immune function and improving broiler growth performance.

Luminescence quenching in aqueous environments poses a challenge for practical applications. Lanthanide-doped up-conversion nanoparticles (UCNPs), representative of near-infrared (NIR)-emitting phosphors, typically utilize Yb³⁺ ions as sensitizers, requiring 980 nm light. This wavelength coincides with the transitions of water molecules, interfering with population dynamics, and continuous irradiation causes unintended heating. Although Nd³⁺ ions, which absorb at 800 nm, serve as alternative sensitizers, their practical use is limited by low quantum yield (Q.Y.). In this study, we developed water-insensitive down-shifting nanoparticles (WINPs) functioning within the NIR-I range (700–900 nm) to avoid water interference. Characterization through single-particle-level spectroscopy demonstrated water-insensitive properties, with identical powers density and lifetime profiles under both dry and water conditions. The WINPs achieved a high Q.Y. of 22.1 ± 0.9%, allowing operation at a detection limit power 15-fold lower than UCNPs, effectively eliminating background noise and enhancing overall performance. To assess diagnostic potential, we validated WINP-based lateral flow immunoassay (LFA) for detecting avian influenza viruses (AIVs) in 65 opaque clinical samples, achieving 100% sensitivity and an area under the curve (AUC) of 1.000 at only 100 mW cm⁻². These findings highlight the potential of WINPs as water-insensitive NIR phosphors that can operate at low power, even in water-rich environments.

The MINFLUX concept significantly improves the localization properties of single-molecule localization microscopy (SMLM) by overcoming the limit imposed by the fluorophore’s photon counts. Typical MINFLUX microscopes localize the target molecule by scanning a zero-intensity focus around the molecule in a circular trajectory, with smaller trajectory diameters yielding better localization uncertainties for a given number of photons. Since this approach requires the molecule to be within the scanned trajectory, MINFLUX typically relies on an iterative scheme with decreasing trajectory diameters. This iterative approach is prone to misplacements of the trajectory and increases the system’s complexity. In this work, we introduce ISM-FLUX, a novel implementation of MINFLUX using image-scanning microscopy (ISM) with a single-photon avalanche diode array detector. ISM-FLUX provides a precise MINFLUX localization within the trajectory while maintaining a conventional photon-limited uncertainty outside it. The robustness of ISM-FLUX localization results in a larger localization range and greatly simplifies the architecture, which may facilitate broader adoption of MINFLUX.