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Quantum photonic integrated circuits are reshaping quantum networks and sensing by providing compact, efficient platforms for practical quantum applications. Despite continuous breakthroughs, integrating entangled registers into photonic devices on a CMOS-compatible platform presents significant challenges. Herein, we present single electron-nuclear spin entanglement and its integration into a silicon-carbide-on-insulator (SiCOI) waveguide. We demonstrate the successful generation of single divacancy electron spins and near-unity spin initialization of single 13C nuclear spins. Both single nuclear and electron spin can be coherently controlled and a maximally entangled state with a fidelity of 0.89 has been prepared under ambient conditions. Based on the nanoscale positioning techniques, the entangled quantum register has been further integrated into SiC photonic waveguides for the first time. We find that the intrinsic optical and spin characteristics of the register are well preserved and the fidelity of the entangled state remains as high as 0.88. Our findings highlight the promising prospects of the SiCOI platform as a compelling candidate for future scalable quantum photonic applications. Silicon-carbide-on-insulator is a promising platform for scalable quantum photonic circuits. Here the authors demonstrate the integration of a single electron-nuclear spin register into silicon-carbide-on-insulator waveguides, which is an important step toward CMOS-compatible quantum photonic devices. [ABSTRACT FROM AUTHOR]

Savannas are widespread biomes with highly valued ecosystem services. To successfully manage savannas in the future, it is critical to better understand the long-term dynamics of their productivity and phenology. However, accurate large-scale gross primary productivity (GPP) estimation remains challenging because of the high spatial and seasonal variations in savanna GPP. China's savanna ecosystems constitute only a small part of the world's savanna ecosystems and are ecologically fragile. However, studies on GPP and phenological changes, while closely related to climate change, remain scarce. Therefore, we simulated savanna ecosystem GPP via a satellite-based vegetation photosynthesis model (VPM) with fine-resolution harmonized Landsat and Sentinel-2 (HLS) imagery and derived savanna phenophases from phenocam images. From 2015 to 2018, we compared the GPP from HLS VPM (GPPHLS-VPM) simulations and that from Moderate-Resolution Imaging Spectroradiometer (MODIS) VPM simulations (GPPMODIS-VPM) with GPP estimates from an eddy covariance (EC) flux tower (GPPEC) in Yuanjiang, China. Moreover, the consistency of the savanna ecosystem GPP was validated for a conventional MODIS product (MOD17A2). This study clearly revealed the potential of the HLS VPM for estimating savanna GPP. Compared with the MODIS VPM, the HLS VPM yielded more accurate GPP estimates with lower root-mean-square errors (RMSEs) and slopes closer to 1:1. Specifically, the annual RMSE values for the HLS VPM were 1.54 (2015), 2.65 (2016), 2.64 (2017), and 1.80 (2018), whereas those for the MODIS VPM were 3.04, 3.10, 2.62, and 2.49, respectively. The HLS VPM slopes were 1.12, 1.80, 1.65, and 1.27, indicating better agreement with the EC data than the MODIS VPM slopes of 2.04, 2.51, 2.14, and 1.54, respectively. Moreover, HLS VPM suitably indicated GPP dynamics during all phenophases, especially during the autumn green-down period. As the first study that simulates GPP involving HLS VPM and compares satellite-based and EC flux observations of the GPP in Chinese savanna ecosystems, our study enables better exploration of the Chinese savanna ecosystem GPP during different phenophases and more effective savanna management and conservation worldwide. [ABSTRACT FROM AUTHOR]

The manipulation of light has become the focus of various modern optical technologies. The emergence of bound states in the continuum (BICs) offers an alternative platform for controlling light, including the confinement and manipulation of polarization, amplitude, and phase. Currently, research on photonic BICs is maturing, with extensive exploration of methods for achieving BICs and their various applications, including lasing, sensing, and enhanced light‐matter interaction. In this review, an overview of photonic BICs is provided. Specifically, the unique properties of BICs are first presented, followed by their state‐of‐the‐art applications in passive systems, ranging from sensing to waveguiding, beam shaping, and chirality. The paradigm‐shifting developments in active systems resulting from the hybridization of BICs with active and novel materials are then highlighted. Finally, some of the challenges facing photonic BICs are discussed, along with future directions in terms of physics, design, fabrication, engineering, and tunability. [ABSTRACT FROM AUTHOR]

We introduce a new paradigm for generating high-purity vortex beams with metasurfaces. By applying optical neural networks to a system of cascaded phase-only metasurfaces, we demonstrate the efficient generation of high-quality Laguerre-Gaussian (LG) vortex modes. Our approach is based on two metasurfaces where one metasurface redistributes the intensity profile of light in accord with Rayleigh-Sommerfeld diffraction rules, and then the second metasurface matches the required phases for the vortex beams. Consequently, we generate high-purity LGp,l optical modes with record-high Laguerre polynomial orders p = 10 and l = 200, and with the purity in p, l and relative conversion efficiency as 96.71%, 85.47%, and 70.48%, respectively. Our engineered cascaded metasurfaces suppress greatly the backward reflection with a ratio exceeding −17 dB. Such higher-order optical vortices with multiple orthogonal states can revolutionize next-generation optical information processing. The authors demonstrate an efficient way to generate high-purity vortex beams by applying optical neural networks to cascaded phase-only metasurfaces. Specifically, they present record-high-quality Laguerre-Gaussian (LGp,l) optical modes with polynomial orders p = 10 and l = 200 with purity in p, l and relative conversion efficiency of 96%, 85%, and 70%, respectively. [ABSTRACT FROM AUTHOR]

The on‐chip meta‐lenses consisting of subwavelength slot arrays with lateral gradients have shown great potential for parallel signal processing and optical computing. The dynamic tuning mechanisms which are necessary steps toward exploiting the applications of the on‐chip meta‐system have been rarely mentioned yet. Here, a free‐form functional microheater via topology design is proposed to manipulate the refractive index distribution, allowing for flexible optical wavefront shaping. For a proof‐of‐concept, wide range of dynamic focusing and beam steering are demonstrated via a tunable meta‐lens on silicon photonic platform. The continuous scanning of the focused beam is experimentally achieved with a maximum travel range of 100 µm in the longitudinal direction (≈95 nm mW−1) and 25 µm in the lateral direction (≈20 nm mW−1). The thermal‐optic tuning elements can response the electrical control within ≈41.2 µs. A waveguide array at the focal plane is used to characterize the device. The on‐chip loss of the tunable meta‐lens is measured to be <1 dB including the coupling loss from slab to single‐mode waveguide. The proposed tunable meta‐lenses are fabricated via a standard silicon photonic process and allow for arbitrarily two dimensional (2D) beam steering. It offers great versatility for on‐chip meta‐systems with a wider scope of functionalities and applications. [ABSTRACT FROM AUTHOR]

Diffractive gratings are crucial elements for optical systems but suffer from rapid power drop at large angles. Recently, metagratings have shown their capability of deflecting light in an arbitrary direction. However, the experimental efficiency at large‐angle is still low and the zeroth‐order crosstalk is difficult to suppress. Here a new approach for large‐angle and high‐efficiency anomalous refraction in the visible spectrum is demonstrated. By introducing out‐of‐plane asymmetry, it is shown that meta‐atoms with simple configurations have similar degrees of freedom as their topologically optimized counterparts. Consequently, the slanted titanium dioxide (TiO2) metagratings can steer light to 80° with high relative efficiency (98.5%) and absolute efficiency (89.5%), which represents the ratio of the energy in target diffraction order to the total transmittance energy and to the total incident energy, respectively. Most importantly, the simple configurations make the TiO2 metagratings easy to fabricate, and the experimental efficiency for large (80°) angle of refraction is preserved at a considerably high value of 94.0% (relative) and 83.6% (absolute). This approach represents an effective route in meta‐devices and shall trigger new classes of high‐performance nanophotonic systems. [ABSTRACT FROM AUTHOR]

The quantification of large-scale leaf-age-dependent leaf area index has been lacking in tropical and subtropical evergreen broadleaved forests (TEFs), despite the recognized importance of leaf age in influencing leaf photosynthetic capacity in this biome. Here, we simplified the canopy leaves of TEFs into three age cohorts (i.e., young, mature, and old, with different photosynthesis capacities; i.e., Vc,max) and proposed a novel neighbor-based approach to develop the first gridded dataset of a monthly leaf-age-dependent leaf area index (LAI) product (referred to as Lad-LAI) at 0.25 ∘ spatial resolution over the continental scale during 2001–2018 from satellite observations of sun-induced chlorophyll fluorescence (SIF) that was reconstructed from MODIS and TROPOMI (the TROPOspheric Monitoring Instrument). The new Lad-LAI products show good performance in capturing the seasonality of three LAI cohorts, i.e., young (LAI young ; the Pearson correlation coefficient of R=0.36), mature (LAI mature ; R=0.77), and old (LAI old ; R=0.59) leaves at eight camera-based observation sites (four in South America, three in subtropical Asia, and one in the Democratic Republic of the Congo (DRC)) and can also represent their interannual dynamics, validated only at the Barro Colorado site, with R being equal to 0.54, 0.64, and 0.49 for LAI young , LAI mature , and LAI old , respectively. Additionally, the abrupt drops in LAI old are mostly consistent with the seasonal litterfall peaks at 53 in situ measurements across the whole tropical region (R=0.82). The LAI seasonality of young and mature leaves also agrees well with the seasonal dynamics of the enhanced vegetation index (EVI; R=0.61), which is a proxy for photosynthetically effective leaves. Spatially, the gridded Lad-LAI data capture a dry-season green-up of canopy leaves across the wet Amazonian areas, where mean annual precipitation exceeds 2000 mm yr -1 , consistent with previous satellite-based analyses. The spatial patterns clustered from the three LAI cohorts also coincide with those clustered from climatic variables over the whole TEF region. Herein, we provide the average seasonality of three LAI cohorts as the main dataset and their time series as a supplementary dataset. These Lad-LAI products are available at 10.6084/m9.figshare.21700955.v4 (Yang et al., 2022). [ABSTRACT FROM AUTHOR]

Metal halide perovskite single crystals are promising for diverse optoelectronic applications due to their outstanding properties. In comparison to the bulk, the crystal surface suffers from high defect density and is moisture sensitive; however, surface modification strategies of perovskite single crystals are relatively deficient. Herein, solar cells based on methylammonium lead triiodide (MAPbI3) thin single crystals are selected as a prototype to improve single‐crystal perovskite devices by surface modification. The surface trap passivation and protection against moisture of MAPbI3 thin single crystals are achieved by one bifunctional molecule 3‐mercaptopropyl(dimethoxy)methylsilane (MDMS). The sulfur atom of MDMS can coordinate with bare Pb2+ of MAPbI3 single crystals to reduce surface defect density and nonradiative recombination. As a result, the modified devices show a remarkable efficiency of 22.2%, which is the highest value for single‐crystal MAPbI3 solar cells. Moreover, MDMS modification mitigates surface ion migration, leading to enhanced reverse‐bias stability. Finally, the cross‐link of silane molecules forms a protective layer on the crystal surface, which results in enhanced moisture stability of both materials and devices. This work provides an effective way for surface modification of perovskite single crystals, which is important for improving the performance of single‐crystal perovskite solar cells, photodetectors, X‐ray detectors, etc. [ABSTRACT FROM AUTHOR]

As a fundamental building block for photonic integrated circuits, waveguide crossing is playing an essential role for routing the increasingly complex network on chip. Driven by the demands for carrying a large capacity of data per waveguide, wavelengths and guiding modes are emerging as important degrees of freedom for optical multiplexing to embrace the advantages of signal parallelism. Although various waveguide crossing structures are proposed to either support broad spectra of wavelengths or a large number of modes, none of these are simultaneously achieved. Here, an ultra‐broadband multimode waveguide crossing based on subwavelength transmitarray (SWTA) is proposed. The SWTA is well designed for high transmittance in the propagation direction and excellent confinement in its orthogonal direction by creation of a bound state. A three‐mode crossing is designed and fabricated on silicon on insulator with a compact footprint of only 5.05 µm × 5.05 µm. The crossing is able to operate over a large bandwidth from 1.4 to 2.1 µm with an excess loss of less than 0.77 dB. For a proof‐of‐concept demonstration of the structure scalability, the crossing is predicted to support up to ten modes. The ultra‐broadbandwidth and compactness of this multimode crossing make it possible to densely cross connect the waveguides with large data capacity via wavelength and mode division multiplexing. [ABSTRACT FROM AUTHOR]

Optical computing has a series of advantages over its electronic counterpart, e.g., low energy consumption, high speed, and intrinsic parallelism. Diffraction deep neural networks (D2NNs) are a prominent example capable of processing images directly without addressing the spatial locations of each element. Despite the great successes, the D2NNs typically utilize the multilayer framework and face the severe challenge of misalignment in the optical region. Herein, a single metasurface‐based optical‐electronic hybrid neural network (OENN) is proposed and experimentally demonstrated. The OENN is composed of a titanium dioxide (TiO2) metasurface and a fully‐connected electronic layer. The combination of nonlocal neural layer and nonlinear transformation has significantly expanded the neural network capacity. Consequently, the classification accuracy on handwritten digits recognition can still be as high as 98.05% without employing the architecture of cascaded metasurfaces. The OENN shall shed light on the practical applications of optical computing in the visible spectrum. [ABSTRACT FROM AUTHOR]

Many breakthroughs in technologies are closely associated with the deep understanding and development of new material platforms. As the main material used in microelectronics, Si also plays a leading role in the development of integrated photonics. The indirect bandgap, absence of χ(2) nonlinearity and the parasitic nonlinear absorptions at the telecom band of Si imposed technological bottlenecks for further improving the performances and expanding the functionalities of Si microcavities in which the circulating light intensity is dramatically amplified. The past two decades have witnessed the burgeoning of the novel material platforms that are compatible with the complementary metal-oxide-semiconductor (COMS) process. In particular, the unprecedented optical properties of the emerging materials in the thin film form have resulted in revolutionary progress in microcavity photonics. In this review article, we summarize the recently developed material platforms for integrated photonics with the focus on chip-scale microcavity devices. The material characteristics, fabrication processes and device applications have been thoroughly discussed for the most widely used new material platforms. We also discuss open challenges and opportunities in microcavity photonics, such as heterogeneous integrated devices, and provide an outlook for the future development of integrated microcavities. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) lasers with dynamic wavelength‐tunability and high monochromaticity are crucial in a multitude of practical applications yet still remarkable challenges. Here, we show wide wavelength‐tuning of single‐mode UV lasing based on lanthanide‐doped upconversion nanoparticles (UCNPs). The rationally designed Yb3+/Er3+/Tm3+/Gd3+/Ce3+ co‐doped multilayer UCNPs, which exhibits a broad gain spectrum with the full width of half maximum of around 57 nm in the UV regime, are developed. More importantly, by taking advantages of a diffraction grating as the tuning component, stable single‐mode emission can be achieved in the UCNPs‐based external‐cavity‐extended Fabry–Pérot laser at room temperature. Specifically, the lasing threshold is around 137 µJ cm–2, which is two orders of magnitude lower than that in the previously reported articles. Precise wavelength‐tuning from 310 to 363 nm can be realized by adjusting the Littrow angle. This achievement highlights a portable alternative to continuously wideband‐tunable UV lasers and opens up new opportunities for constructing compact solid‐state UV photon sources. [ABSTRACT FROM AUTHOR]

The integration density and the system complexity of photonic integrated circuits are scaling significantly, especially for optical computing, signal processing, and other emerging applications. As is such, the quest for information multiplexing is becoming increasingly important. On-chip mode division multiplexing (MDM) is considered to be a promising solution which is capable of processing a large amount of data via intrinsic parallelism. Various device structures have been proposed for on-chip mode multiplexing while most of which either lack the scalability or occupy too much chip area. Here, a scalable and compact silicon photonic mode (de)multiplexer is proposed and experimentally demonstrated based on tilt waveguide junctions assisted with shallow-etched subwavelength slots. The number of channels can be easily scaled by cascading multiple junctions. Compared with conventional cascaded structures, the proposed shallow etched slots enable a new mode evolution scheme which significantly shrinks the device length. For a proof-of-concept demonstration, four-mode (de)multiplexer for TE0–TE3 modes is designed, fabricated, and characterized. The measured insertion losses for all four modes are below 1.29 dB, while the crosstalks are all below −14.4 dB. [ABSTRACT FROM AUTHOR]

Schizophrenia (SZ) is a severe neuropsychiatric disorder with largely unknown etiology and pathogenesis. Mounting preclinical and clinical evidence suggests that the gut microbiome is a vital player in SZ. However, the gut microbiota characteristics and its host response in elderly SZ patients are still not well understood. A total of 161 samples was collected, including 90 samples from elderly SZ patients and 71 samples from healthy controls. We explored the gut microbiota profiles targeting the V3–V4 region of the 16S rRNA gene by MiSeq sequencing, and to analyze their associations with host immune response. Our data found that bacterial β-diversity analyses could divide the SZ patients and healthy controls into two different clusters. The Linear discriminant analysis Effect Size (LEfSe) identified the compositional changes in SZ-associated bacteria, including Faecalibacterium , Roseburia , Actinomyces , Butyricicoccus , Prevotella and so on. In addition, the levels of pro-inflammatory cytokines such as IL-1β were greatly increased in SZ patients while the levels of anti-inflammatory cytokines such as IFN-γ were markedly decreased. Correlation analysis suggested that these bacteria contributed to immune disturbances in the host that could be used as non-invasive biomarkers to distinguish the SZ patients from healthy controls. Moreover, several predicted functional modules, including increased lipopolysaccharide biosynthesis, folate biosynthesis, lipoic acid metabolism, and decreased bile acid biosynthesis, fatty acid biosynthesis in SZ-associated microbiota, could be utilized by the bacteria to produce immunomodulatory metabolites. This study, for the first time, demonstrated the structural and functional dysbiosis of the fecal microbiota in Chinese elderly SZ patients, suggesting the potential for using gut key functional bacteria for the early, non-invasive diagnosis of SZ, personalized treatment, and the development of tailor-made probiotics designed for Chinese elderly SZ patients. [ABSTRACT FROM AUTHOR]

2 Multifunctionality from the pattern design Polarization [[65]], [[66]], [[67]], [[68]], [[69]], wavelength [[20], [24], [69]], [[70]], [[71]], and angle [[72]], [[73]], [[74]], [[75]] of incidence are part of a non-exhaustive list of parameters of a given light source that are usually taken advantage of as multiplexing channels for the multifunctional metasurfaces [[21]], which realize holography, structural color, and beam steering at the same time. Keywords: multifunctional; optical metasurface; reconfigurable; tunable EN multifunctional optical metasurface reconfigurable tunable 1761 1781 21 05/12/22 20220401 NES 220401 1 Introduction The ability to control the wavefront of light is fundamental to focalization and redistribution of light, enabling many applications from imaging to spectroscopy. Although only the function of holography can be tuned, the vectorial holography that relies on polarization of incident light will bring more information channels, which is vital for optical encryption. Matrix Fourier optics enables polarization multiplexing in holograms [[77]]. [Extracted from the article]

The development of multi-wavelength lasing, particularly with the wavelength tuning in a wide spectral range, is challenging but highly desirable for integrated photonic devices due to its dynamic switching functionality, high spectral purity and contrast. Here, we propose a general strategy, that relies on the simultaneous design on the electronic states and the optical states, to demonstrate dynamically switchable single-mode lasing spanning beyond the record range (300 nm). This is achieved through integrating the reversely designed nanocrystals with two size-mismatched coupled microcavities. We show an experimental validation of a crosstalk-free violet-to-red single-mode behavior through collective control of asymmetric excitation and excitation wavelength. The single-mode action persists for a wide power range, and presents significant enhancement when compared with that in the microdisk laser. These findings enlighten the reverse design of luminescent materials. Given the remarkable doping flexibility, our results may create new opportunities in a variety of frontier applications. Dual-wavelength lasers are gaining importance for photonic applications. In this work the authors demonstrate that by incorporating a lanthanidedoped material into the size-mismatched coupled microcavities, it is possible to achieve laser switch with high uniformity, long-term stability, and an extremely wide spectral range up to 300 nm [ABSTRACT FROM AUTHOR]

The atmospheric methane (CH4) concentration has increased in recent years due to natural and anthropogenic causes. Hence, it is essential to quantify the potential sources of CH4 to understand the factors responsible for its fluxes on a local to regional scale through in situ observations. Coastal wetlands, particularly the mangrove ecosystems in the tropical and subtropical coasts, are significant sources of CH4. In this study, we used an eddy covariance-based technique to measure the CH4 fluxes in a mangrove ecosystem in Pichavaram, South India. The daily mean CH4 flux ranged from 12 to 26 nmol m−2 s−1 during the wet season and from 6 to 20 nmol m–2 s–1 during the dry season. The monthly mean flux during the wet period was between 0.8 and 1.8 g CH4 m−2 month−1, and in the dry season, it was between 0.4 and 0.6 g CH4 m−2 month−1. The visual correlogram and structural equation modelling technique revealed that air temperature, creek water dissolved oxygen, soil organic carbon, and redox potential are important factors that control the CH4 fluxes. The results suggest that the Pichavaram mangrove wetland acts as a source for CH4. Our results also indicate that tidal inundation and seasonal variations in atmospheric temperature and water salinity are key factors affecting the CH4 flux in the Pichavaram mangrove ecosystem. [ABSTRACT FROM AUTHOR]

Kerr optical frequency comb as a novel microcomb source has found a variety of key applications from fundamental research to engineering applications. Generation of such microcombs require resonator platforms with small mode volumes and high quality factors, where the interaction of light and matter is resonantly enhanced. In these platforms, other nonlinear photonic effects can be simultaneously excited and interact with Kerr frequency combs. In this review, the focus is on recent progresses on the microcomb development involving its interaction with Raman, Brillouin scattering, and second‐order nonlinear processes such as second harmonic generation (SHG). The resulting transfer of Kerr frequency combs into other spectral windows as referred to Kerr–Raman, Kerr–Brillouin, Kerr–SHG combs is introduced. Additionally, other emerging novel microcombs in microresonators with second‐order nonlinearity including electro‐optical modulation microcombs and quadratic microcombs are reviewed. Challenges and opportunities brought along are also discussed. [ABSTRACT FROM AUTHOR]

Subtropical forests are important ecosystems globally due to their extensive role in carbon sequestration. Extreme climate events are known to introduce disturbances in the ecosystem that cause long‐term changes in carbon balance and radiation reflectance. However, how these ecosystem function changes contribute to global warming in terms of radiative forcing (RF), especially in the years following a disturbance, still needs to be investigated. We studied an extreme snow event that occurred in a subtropical evergreen broadleaved forest in south‐western China in 2015 and used 9 years (2011–2019) of net ecosystem CO2 exchange (NEE) and surface albedo (α) data to investigate the effect of the event on the ecosystem RF changes. In the year of the disturbance, leaf area index (LAI) declined by 40% and α by 32%. The annual NEE was −718 ± 128 g C m−2 as a sink in the pre‐disturbance years (2011–2014), but after the event, the sink strength dropped significantly by 76% (2015). Both the vegetation, indicated by LAI, and α recovered to pre‐disturbance levels in the fourth post‐disturbance year (2018). However, the NEE recovery lagged and occurred a year later in 2019, suggesting a more severe and lasting impact on the ecosystem carbon balance. Overall, the extreme event caused a positive (warming effect) net RF which was predominantly caused by changes in α (90%–93%) rather than those in NEE. This result suggests that, compared to the climate effect caused by forest carbon sequestration changes, the climate effect of α alterations can be more sensitive to vegetation damage induced by natural disturbances. Moreover, this study demonstrates the important role of vegetation recovery in driving canopy reflectance and ecosystem carbon balance during the post‐disturbance period, which determines the ecosystem feedbacks to the climate change. [ABSTRACT FROM AUTHOR]

We conducted a three-month field experiment focusing on the physical and chemical characteristics of fog in a tropical rainforest in Xishuangbanna, Southwest China, in the winter of 2019. In general, the fog would form at midnight and persist because of the increased long-wave radiative cooling combined with the high relative humidity, gentle breeze, and a relatively low aerosol number concentration in the forest; the fog would dissipate before noon due to the increasing turbulence near the surface. This diurnal cycle is typical for radiation fog. The microphysical fog properties included a relatively low number concentration of the fog droplet, large droplet size, high liquid water content, narrow droplet number-size distribution, and high supersaturation. The chemical properties showed that the fog water was slightly alkaline with low electrical conductivity, whereas the highest proportions of anions and cations therein were Cl− and Ca2+, respectively; the chemical components were enriched in small fog droplets. In addition, we indirectly calculated the fog supersaturation according to the κ-Köhler theory. We found that condensation broadens the droplet number-size distribution at relatively low supersaturation, which is positively correlated with the fog-droplet number concentration and negatively correlated with the droplet mean-volume diameter; this affects the key microphysical processes of fog. [ABSTRACT FROM AUTHOR]

Over the past years, broadband achromatic metalenses have been intensively studied due to their great potential for applications in consumer and industry products. Even though significant progress has been made, the efficiency of technologically relevant silicon metalenses is limited by the intrinsic material loss above the bandgap. In turn, the recently proposed achromatic metalens utilizing transparent, high-index materials such as titanium dioxide has been restricted by the small thickness and showed relatively low focusing efficiency at longer wavelengths. Consequently, metalens-based optical imaging in the biological transparency window has so far been severely limited. Herein, we experimentally demonstrate a polarization-insensitive, broadband titanium dioxide achromatic metalens for applications in the near-infrared biological imaging. A large-scale fabrication technology has been developed to produce titanium dioxide nanopillars with record-high aspect ratios featuring pillar heights of 1.5 µm and ~90° vertical sidewalls. The demonstrated metalens exhibits dramatically increased group delay range, and the spectral range of achromatism is substantially extended to the wavelength range of 650–1000 nm with an average efficiency of 77.1%–88.5% and a numerical aperture of 0.24–0.1. This research paves a solid step towards practical applications of flat photonics. Though broadband achromatic metalens are attractive for biological applications, existing metalenses show limited performance in the biological imaging window. Here, the authors report high-efficiency broadband achromatic metalens featuring record-high aspect ratio titanium dioxide metasurfaces. [ABSTRACT FROM AUTHOR]

Polarization and mode division multiplexing are powerful tools for large-capacity parallel optical communications. Dual-polarization and mode-division multiplexed silicon photonic integrated circuit with ultra-small footprint is proposed and experimentally demonstrated. The circuits consist of a mode multiplexer, 3-dB power splitter and two demultiplexers which can simultaneously handle TE0, TE1, TM0 and TM1 mode. Compared with conventional device structure, the device footprint is scaled down via pixelated waveguide meta-structure. The mode multiplexer and the splitter have a footprint of only 6.8 μm × 6 μm and 6 μm × 5.25 μm, respectively. The fabrication tolerance on the nanohole size variations are studied, and the fabricated devices are systematically characterized. The measured insertion losses of the multiplexer and 3-dB power splitter are below 1.4 dB and 4.5 dB for all four modes within the wavelength range from 1530 nm-1570 nm. In the meantime, the measured maximum inter-mode cross talk is below -15 dB over a 30 nm bandwidth. The experimental results also indicate the power imbalance of the splitter is within 0.4 dB from 1530 nm-1570 nm. Since the demonstrated polarization and mode handling devices via pixelated meta-structures occupy significantly smaller chip area than conventional wisdoms, this work shows the potential for large scale and dense integration of polarization and mode division multiplexing system on photonic chip. [ABSTRACT FROM AUTHOR]

Structural coloration generates colors by the interaction between incident light and micro- or nano-scale structures. It has received tremendous interest for decades, due to advantages including robustness against bleaching and environmentally friendly properties (compared with conventional pigments and dyes). As a versatile coloration strategy, the tuning of structural colors based on micro- and nanoscale photonic structures has been extensively explored and can enable a broad range of applications including displays, anti-counterfeiting, and coating. However, scholarly research on structural colors has had limited impact on commercial products because of their disadvantages in cost, scalability, and fabrication. In this review, we analyze the key challenges and opportunities in the development of structural colors. We first summarize the fundamental mechanisms and design strategies for structural colors while reviewing the recent progress in realizing dynamic structural coloration. The promising potential applications including optical information processing and displays are also discussed while elucidating the most prominent challenges that prevent them from translating into technologies on the market. Finally, we address the new opportunities that are underexplored by the structural coloration community but can be achieved through multidisciplinary research within the emerging research areas. [ABSTRACT FROM AUTHOR]

Structural color, which generates vivid colors via the geometrical arrangement of resonant nanostructures, can enhance the recyclability and mechanical stability of colors; structural colors have been intensively studied in recent years, owing to their high resolution, color purity, and stability compared to colors generated by dyes and pigments. Dielectric materials, which possess a suitably high refractive index and low loss in the visible range, are ideal materials for structural colors. However, the static optical performances of most structural colors impose restrictions on their applicability. This article reviews the fundamental physics of dielectric structural color procedures based on Mie resonance; furthermore, it highlights recent progress in tunable structural colors, focusing on their operation mechanisms and practical applications, including the geometric parameters of the nanostructures, optical parameters of the building materials and environments, and properties of the optical stimuli. This article is concluded by presenting an outlook on the future potential of structural colors, as well as the challenges that remain to be addressed. [ABSTRACT FROM AUTHOR]

Silicon photonic optical phased arrays are promising solutions for solid-state LIDAR. But the nonlinear absorption significantly saturates the optical power in the waveguides at 1.5-μm wavelengths. Besides, the high refractive index contrast of silicon grating exhibits a strong diffraction strength of the antenna, which results in a limited aperture of the device. These ultimately place a limit on the detection accuracy and reach. Here, a shallow etched two-dimensional subwavelength grating structure is proposed to improve the efficiency and aperture of the waveguide antenna. A reduction of diffraction strength is achieved via nanohole structure instead of conventional grating lines. Thus, a millimeter-long optical antenna is demonstrated with a peak efficiency of 71%. The far-field diffracted beam width of 0.035° and vertical field-of-view of 17.5° are achieved within 100 nm wavelengths range from 1.95 μm to 2.05 μm. The operation at 2-μm waveband also guarantees better eye-safety and significantly reduces the nonlinear absorption in silicon waveguide compared with conventional 1.5-μm band. [ABSTRACT FROM AUTHOR]

The delicate nature of optical components requires very special handling and storage procedures to maximize their performance and lifetime. In the optical field, a long‐standing challenge is the cleaning of unavoidable contaminants during the daily use, especially for the coated elements and the biomedical diagnostic devices. Herein, the authors tackle this problem and experimentally demonstrate TiO2 based self‐cleaning optical meta‐devices with the illuminating of UV light. By arranging TiO2 nanopillars into different patterns, high‐efficiency TiO2 meta‐devices have been realized for the visible spectrum, for example, color nano‐printings, metalenses, and meta‐holograms. The TiO2 meta‐devices become hydrophilic and photoactive under UV irradiation. Consequently, the contaminants, such as, stearic acid or fingerprints have been completely cleaned. Owing to the stability of TiO2, the self‐cleaning effect and the internal nanostructures of meta‐devices are well preserved for many rounds of contamination. This research shall bring new opportunities to TiO2 metasurfaces for extreme applications. [ABSTRACT FROM AUTHOR]

With their ultrathin characteristics as well as the powerful and flexible capabilities of wavefront modulation, optical metasurfaces have brought a new understanding of the interaction between light and matter and provided a powerful way to constrain and manage light. However, the unmodifiable structures and the immutable materials used in the construction lead to the unsatisfactory applications in most functional devices. The emergence of tunable optical metasurfaces breaks the aforementioned limitations and enables us to achieve dynamic control of the optical response. The work in recent years has focused on achieving tunability of optical metasurfaces through material property transition and structural reconfiguration. In this review, some tunable optical metasurfaces in recent years are introduced and summarized, as well as the advantages and limitations of various materials and mechanisms used for this purpose. The corresponding applications in functional devices based on tunability are also discussed. The review is terminated with a short section on the possible future developments and perspectives for future applications. [ABSTRACT FROM AUTHOR]

Meta-holographic encryption is a potentially important technique for information security. Despite rapid progresses in multi-tasked meta-holograms, the number of information channels available in metasurfaces is limited, making meta-holographic encryption vulnerable to some attacking algorithms. Herein, we demonstrate a re-programmable metasurface that can produce arbitrary holographic images for optical encryption. The encrypted information is divided into two matrices. These two matrices are imposed to the incident light and the metasurface, respectively. While the all-dielectric metasurface is static, the phase matrix of incident light provides additional degrees of freedom to precisely control the eventual functions at will. With a single Si metasurface, arbitrary holographic images and videos have been transported and decrypted. We hope that this work paves a more promising way to optical information encryption and authentication.Here, the authors demonstrate a re-programmable metasurface that can produce arbitrary holographic images for optical encryption. The encrypted information is divided into two matrices and defined to the incident laser to produce arbitrary holographic images. [ABSTRACT FROM AUTHOR]

Formamidinium (CH(NH2)2, FA) lead halide perovskites exhibit excellent optoelectronic properties for the applications of light‐emitting diodes and lasers. However, the reported formamidinium lead bromide (FAPbBr3) perovskite‐based lasers mainly depend on the external feedback or Fabry–Pérot mode cavities and suffer from moderate quality (Q) factors. Herein, solution‐processed square and quasi‐circular FAPbBr3 microdisks are developed to achieve room‐temperature naturally facet‐formed whispering gallery mode (WGM) lasers. These microdisks exhibit relatively high Q factor and tunable laser modes with threshold of 10–70 µJ cm−2 under 400 nm excitation. Although the synthesized circular microdisk is not regular enough, it still shows higher Q factor of 3455 than that of square microdisk due to the less boundary wave and pesudointegrable leakage. This simple and low‐cost solution processed method can tackle the complicated and expensive conventional preparation techniques of circular microdisks. Power dependent photoluminescence decay transients indicate that the band edge emission of the FAPbBr3 microdisks originates from free carrier recombination. In addition, these microdisks show high photostability and that room temperature lasing can sustain over 50 min. These results suggest that FAPbBr3 microdisks can serve as promising WGM lasers with excellent light emission capability and stability toward practical optoelectronic applications. [ABSTRACT FROM AUTHOR]

Integration of microcavity‐based coherent light sources and waveguides is of central importance for building optical networks and photonic circuits. However, such combined devices face severe challenges in distributing the generated signals to designed ends despite that the significant advances are accomplished in emission modulation and controlling. Herein, dynamically all‐optical control of the outputs from the microcavity by employing parity‐time (PT) symmetry is demonstrated. By exploiting the interplay between gain and loss in a waveguide‐connected microsquare cavity, the mode field distributions can be strongly modified when the non‐Hermitian system enters PT‐symmetry breaking phase. Numerical calculations and the corresponding Husimi projections unambiguously show the PT‐symmetry‐induced mode localization and output redistributions in microsquare cavity. Notably, the intensity ratios of the lights collected by the two channels can be directly tuned over two orders of magnitude with the increase of pumping strength. These findings will be essential for understanding the fundamentals of non‐Hermitian optics and advancing the application potentials of microcavity system in integrated photonics. [ABSTRACT FROM AUTHOR]

Lenses are the most important components of portable and integrable optical systems. Due to the inherent limitation of system sizes, external accessories are required for realizing additional functions such as close‐up or telegraph imaging, making the entire system complicated and cumbersome. Herein, based on the developments of metalenses, a spin angular momentum controlled multifunctional camera system is reported. Two types of metalens with high efficiencies are designed and fabricated for circularly polarized and nonpolarized light, respectively. By combining them into a doublet, multiple functions are realized beyond a camera lens. For left‐handed circular polarization light, the doublet works as a compound microscope with a magnification factor of 20 and a resolution of 1.07 µm. The system switches to a Galileo telescope when the incident light turns to be right‐handed circularly polarized. This research shall extend and strengthen the practical applications of metasurfaces in portable imaging systems as well as the integrated sensing terminals. [ABSTRACT FROM AUTHOR]

The achievement of structural color has shown advantages in large-gamut, high-saturation, high-brightness, and high-resolution. While a large number of plasmonic/dielectric nanostructures have been developed for structural color, the previous approaches fail to match all the above criterion simultaneously. Herein we utilize the Si metasurface to demonstrate an all-in-one solution for structural color. Due to the intrinsic material loss, the conventional Si metasurfaces only have a broadband reflection and a small gamut of 78% of sRGB. Once they are combined with a refractive index matching layer, the reflection bandwidth and the background reflection are both reduced, improving the brightness and the color purity significantly. Consequently, the experimentally demonstrated gamut has been increased to around 181.8% of sRGB, 135.6% of Adobe RGB, and 97.2% of Rec.2020. Meanwhile, high refractive index of silicon preserves the distinct color in a pixel with 2 × 2 array of nanodisks, giving a diffraction-limit resolution. Here, the authors fabricate a metasurface with high brightness and large gamut structured colors by combining a silicon metasurface with a refractive index matching layer. The experimentally demonstrated gamut is 181.8% of sRGB, 135.6% of Adobe RGB, and 97.2% of Rec.2020. [ABSTRACT FROM AUTHOR]

While black phosphorus has shown excellent optoelectronic properties in many aspects, the environmental instability ultimately places limits on its practical applications. Black arsenic–phosphorus (b‐AsP), an alloy of black phosphorus with arsenic atoms, has emerged as a new 2D material with better stability. Recently, the heterostructure via integration of 2D material with nanophotonic waveguides is opening an avenue for many on‐chip applications of phosphorene. However, the thermo‐optic (TO) properties, which are widely used for waveguide heaters, are not studied on b‐AsP yet. Herein, the TO effects of a b‐AsP/silicon van der Waals heterostructure are first investigated and its application as a transparent waveguide heater is demonstrated. A high efficiency of 0.74 nm mW−1 is achieved with a nonresonant and broadband heater based on 20 nm thick b‐AsP, which eliminates the need for enhancement by cavity‐assisted light–matter interaction, and thus allows for compact footprint, broadband operation, and low latency. [ABSTRACT FROM AUTHOR]

An ultra-compact and efficient 3-dB power splitter for mode division multiplexing is proposed and demonstrated experimentally in this letter. The device is realized via pixelated meta-structure with a small footprint of only $4\times 4.5\,\,\mu \text{m}^{2}$. The measured results show that the insertion losses and inter-mode crosstalk are lower than 1.5 dB and −15 dB for TE0, TE1 and TE2 modes across the wavelength band of 1530–1570 nm. The measured power imbalance between the two output ports are within 0.35 dB. The tolerances to the fabrication errors and temperature variations are also investigated. The demonstrated three-mode power splitter can directly split the mode multiplexed signals without the need of demultiplexing. Such an integrated functional element helps to significantly increase integration density of photonic integrated circuits. [ABSTRACT FROM AUTHOR]

An ultra-compact mode multiplexer for TE0, TE1, TE2 and TE3 modes is proposed and demonstrated experimentally. The device is realized via pixelated waveguides with a footprint of only $5.4\times 6~\mu \,\,\text{m}^{2}$. The measured insertion loss of the multiplexer is less than 1.5 dB. The inter-mode crosstalk is ~−20 dB at 1550 nm and below −14.6 dB from 1510 nm – 1570 nm. The fabrication and temperature tolerance of the device are investigated. The device can well tolerate the nanohole diameter variation of ±10 nm and the temperature variation of 100 K. The compactness of the proposed mode multiplexer enables potential applications in densely integrated multimode photonic circuits. [ABSTRACT FROM AUTHOR]

The land use change from tropical forests to rubber plantations has had a great influence on ecosystem‐level carbon (C) exchange and soil C dynamics. This study aimed to assess the variation of soil respiration and its components in rubber plantations of different stand age. A trenching method was used to partition soil respiration (RS) into autotrophic respiration (RA) and heterotrophic respiration (RH) for 3 years in 12, 24, 32 and 49‐year‐old rubber plantations. Our results showed that RS changed significantly among rubber plantations, with the highest RS in the old‐growth rubber plantation (49‐year plantation, 147.30 ± 6.91 mg CO2‐C m−2 hr−1) followed by the mature (137.16 ± 7.68 and 108.10 ± 4.83 in 24‐year and 32‐year plantations, respectively) and the young (12‐year plantation, 78.43 ± 3.84 mg CO2‐C m−2 hr−1) rubber plantations. RS was significantly and exponentially related to soil temperature (p < .0001) rather than soil water content, which led to higher RS in the rainy season than in the dry season. The contribution of RA to RS was higher in the mature rubber plantation than in the young (27%) and the old‐growth (20%) rubber plantations. The sensitivity of RS to increasing temperature (Q10) was higher in 32‐ and 49‐year plantations than in 12‐ and 24‐year rubber plantations. The largest Q10 value of RH and RA was found in the old‐growth (49‐year plantation, 2.95) and the mature (32‐year plantation, 8.01) rubber plantations, respectively. Our results highlight the importance of environmental factors in determining the variation in RS in rubber plantations with different stand age. However, further studies are still required to elucidate the mechanisms impacting stand age‐related effects on soil respiration, such as the differences in photosynthesis in rubber plantations. Highlights: Soil respiration (RS) in four rubber plantations of different stand age was examined.RS tended to increase with the increasing stand age.The contribution of autotrophic respiration (RA) to RS was higher in the mature stands.Q10 values of heterotrophic respiration (RH) and RA were higher in old‐growth and mature stands, respectively. [ABSTRACT FROM AUTHOR]

Questions: In the changing climate scenario, the decline in precipitation is expected to alter water availability for plants, which in turn affects plant community structure and composition. The responses of community composition and structure to declines in precipitation are well documented in other biomes but remain understudied in water‐limited savannas. Location: A savanna ecosystem in southwest China. Methods: We used a four‐year (2014–2017) precipitation manipulation experiment to examine changes in herbaceous community composition and structure across the species, functional group and community levels under precipitation reduction. Results: Precipitation reduction significantly decreased the average height and percentage cover of the herbaceous community, while increasing species richness and the Pielou evenness index. Precipitation reduction significantly decreased average height, percentage cover and relative abundance of graminoids and perennials, but increased those of forbs and annuals. Precipitation reduction prompted a shift in the dominant species of the herbaceous community towards Fimbristylis monostachya. Conclusions: The results show that precipitation reduction changed the composition and structure of the herbaceous community of this savanna. Furthermore, they provide strong evidence that changes in herbaceous community structure and composition in response to the intensity and duration of precipitation reduction in this savanna exhibited relatively low thresholds, which suggests that the herbaceous community's response to a decline in precipitation was essentially nonlinear. These findings imply that even relatively small declines in precipitation may stimulate shifts in plant community structure and composition and affect the function and stability of savanna ecosystems. [ABSTRACT FROM AUTHOR]