Microwave photonic technologies, which upshift the carrier into the optical domain, have facilitated the generation and processing of ultra-wideband electronic signals at vastly reduced fractional ...bandwidths. For microwave photonic applications such as radars, optical communications and low-noise microwave generation, optical frequency combs are useful building blocks. By virtue of soliton microcombs, frequency combs can now be built using CMOS-compatible photonic integrated circuits. Yet, currently developed integrated soliton microcombs all operate with repetition rates significantly beyond those that conventional electronics can detect, preventing their use in microwave photonics. Access to this regime is challenging due to the required ultra-low waveguide loss and large dimensions of the nanophotonic resonators. Here, we demonstrate soliton microcombs operating in two widely employed microwave bands, the X-band (~10 GHz, for radar) and the K-band (~20 GHz, for 5G). Driven by a low-noise fibre laser, these devices produce more than 300 frequency lines within the 3 dB bandwidth, and generate microwave signals featuring phase noise levels comparable to modern electronic microwave oscillators. Our results establish integrated microcombs as viable low-noise microwave generators. Furthermore, the low soliton repetition rates are critical for future dense wavelength-division multiplexing channel generation schemes and could significantly reduce the system complexity of soliton-based integrated frequency synthesizers and atomic clocks.Nanophotonic microwave synthesizers in the X-band (10 GHz, for radar) and K-band (20 GHz, for 5G), based on integrated soliton microcombs driven by a low-noise fibre laser, link the fields of microwave photonics and integrated microcombs.
Low-loss photonic integrated circuits and microresonators have enabled a wide range of applications, such as narrow-linewidth lasers and chip-scale frequency combs. To translate these into a ...widespread technology, attaining ultralow optical losses with established foundry manufacturing is critical. Recent advances in integrated Si
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photonics have shown that ultralow-loss, dispersion-engineered microresonators with quality factors Q > 10 × 10
can be attained at die-level throughput. Yet, current fabrication techniques do not have sufficiently high yield and performance for existing and emerging applications, such as integrated travelling-wave parametric amplifiers that require meter-long photonic circuits. Here we demonstrate a fabrication technology that meets all requirements on wafer-level yield, performance and length scale. Photonic microresonators with a mean Q factor exceeding 30 × 10
, corresponding to 1.0 dB m
optical loss, are obtained over full 4-inch wafers, as determined from a statistical analysis of tens of thousands of optical resonances, and confirmed via cavity ringdown with 19 ns photon storage time. The process operates over large areas with high yield, enabling 1-meter-long spiral waveguides with 2.4 dB m
loss in dies of only 5 × 5 mm
size. Using a response measurement self-calibrated via the Kerr nonlinearity, we reveal that the intrinsic absorption-limited Q factor of our Si
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microresonators can exceed 2 × 10
. This absorption loss is sufficiently low such that the Kerr nonlinearity dominates the microresonator's response even in the audio frequency band. Transferring this Si
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technology to commercial foundries can significantly improve the performance and capabilities of integrated photonics.
The last decade has witnessed the remarkable research progress of lanthanide‐doped upconversion nanocrystals (UCNCs) at the forefront of promising applications. However, the future development and ...application of UCNCs are constrained greatly by their underlying shortcomings such as significant nonradiative processes, low quantum efficiency, and single emission colors. Here a hybrid plasmonic upconversion nanostructure consisting of a GNR@SiO2 coupled with NaGdF4:Yb3+,Nd3+@NaGdF4:Yb3+,Er3+@NaGdF4 core–shell–shell UCNCs is rationally designed and fabricated, which exhibits strongly enhanced UC fluorescence (up to 20 folds) and flexibly tunable UC colors. The experimental findings show that controlling the SiO2 spacer thickness enables readily manipulating the intensity ratio of the Er3+ red, green, and blue emissions, thereby allowing us to achieve the emission color tuning from pale yellow to green upon excitation at 808 nm. Electrodynamic simulations reveal that the tunable UC colors are due to the interplay of plasmon‐mediated simultaneous excitation and emission enhancements in the Er3+ green emission yet only excitation enhancement in the blue and red emissions. The results not only provide an upfront experimental design for constructing hybrid plasmonic UC nanostructures with high efficiency and color tunability, but also deepen the understanding of the interaction mechanism between the Er3+ emissions and plasmon resonances in such complex hybrid nanostructure.
The plasmon‐mediated selective excitation and emission enhancement on the blue, green, and red emissions of Er3+ in a rationally designed hybrid plasmonic upconversion (UC) nanostructure enables achieving enhanced UC luminescence and tunable UC color.
The past decade has witnessed major advances in the development and system-level applications of photonic integrated microcombs, that are coherent, broadband optical frequency combs with repetition ...rates in the millimeter-wave to terahertz domain. Most of these advances are based on harnessing of dissipative Kerr solitons (DKS) in microresonators with anomalous group velocity dispersion (GVD). However, microcombs can also be generated with normal GVD using localized structures that are referred to as dark pulses, switching waves or platicons. Compared with DKS microcombs that require specific designs and fabrication techniques for dispersion engineering, platicon microcombs can be readily built using CMOS-compatible platforms such as thin-film (i.e., thickness below 300 nm) silicon nitride with normal GVD. Here, we use laser self-injection locking to demonstrate a fully integrated platicon microcomb operating at a microwave K-band repetition rate. A distributed feedback (DFB) laser edge-coupled to a Si
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chip is self-injection-locked to a high-Q ( > 10
) microresonator with high confinement waveguides, and directly excites platicons without sophisticated active control. We demonstrate multi-platicon states and switching, perform optical feedback phase study and characterize the phase noise of the K-band platicon repetition rate and the pump laser. Laser self-injection-locked platicons could facilitate the wide adoption of microcombs as a building block in photonic integrated circuits via commercial foundry service.
Abstract
Frequency modulated continuous wave laser ranging (FMCW LiDAR) enables distance mapping with simultaneous position and velocity information, is immune to stray light, can achieve long range, ...operate in the eye-safe region of 1550 nm and achieve high sensitivity. Despite its advantages, it is compounded by the simultaneous requirement of both narrow linewidth low noise lasers that can be precisely chirped. While integrated silicon-based lasers, compatible with wafer scale manufacturing in large volumes at low cost, have experienced major advances and are now employed on a commercial scale in data centers, and impressive progress has led to integrated lasers with (ultra) narrow sub-100 Hz-level intrinsic linewidth based on optical feedback from photonic circuits, these lasers presently lack fast nonthermal tuning, i.e. frequency agility as required for coherent ranging. Here, we demonstrate a hybrid photonic integrated laser that exhibits very narrow intrinsic linewidth of 25 Hz while offering linear, hysteresis-free, and mode-hop-free-tuning beyond 1 GHz with up to megahertz actuation bandwidth constituting 1.6 × 10
15
Hz/s tuning speed. Our approach uses foundry-based technologies - ultralow-loss (1 dB/m) Si
3
N
4
photonic microresonators, combined with aluminium nitride (AlN) or lead zirconium titanate (PZT) microelectromechanical systems (MEMS) based stress-optic actuation. Electrically driven low-phase-noise lasing is attained by self-injection locking of an Indium Phosphide (InP) laser chip and only limited by fundamental thermo-refractive noise at mid-range offsets. By utilizing difference-drive and apodization of the photonic chip to suppress mechanical vibrations of the chip, a flat actuation response up to 10 MHz is achieved. We leverage this capability to demonstrate a compact coherent LiDAR engine that can generate up to 800 kHz FMCW triangular optical chirp signals, requiring neither any active linearization nor predistortion compensation, and perform a 10 m optical ranging experiment, with a resolution of 12.5 cm. Our results constitute a photonic integrated laser system for scenarios where high compactness, fast frequency actuation, and high spectral purity are required.
Abstract
The rapidly maturing integrated Kerr microcombs show significant potential for microwave photonics. Yet, state-of-the-art microcomb-based radiofrequency filters have required programmable ...pulse shapers, which inevitably increase the system cost, footprint, and complexity. Here, by leveraging the smooth spectral envelope of single solitons, we demonstrate microcomb-based radiofrequency filters free from any additional pulse shaping. More importantly, we achieve all-optical reconfiguration of the radiofrequency filters by exploiting the intrinsically rich soliton configurations. Specifically, we harness the perfect soliton crystals to multiply the comb spacing thereby dividing the filter passband frequencies. Also, the versatile spectral interference patterns of two solitons enable wide reconfigurability of filter passband frequencies, according to their relative azimuthal angles within the round-trip. The proposed schemes demand neither an interferometric setup nor another pulse shaper for filter reconfiguration, providing a simplified synthesis of widely reconfigurable microcomb-based radiofrequency filters.
Rill erosion accounts for approximately 70% of the total erosion of upland areas in China's Loess Plateau. A laboratory rainfall experiment with deionized water was conducted to examine the process ...of rill evolution and the relationship between runoff, rill evolution, and erosion rates for clay loam and loess soils given a fixed slope gradient (10°) and two rainfall intensities (1.5 and 2.0 mm min−1). The results show that rills evolved from a series of parallel drop‐pit chains along the down‐slope direction. Clay loam soil produced rills under a rainfall intensity of 1.5 mm min−1, and loess soil produced rills only under higher rainfall intensity. The temporal change in sediment concentration and erosion rate shows good consistency with the emergence of drop pits and rills. An increase in rainfall intensity had little effect on the sediment concentration and erosion rate for clay loam soil, whereas for loess soil, both increased rapidly and exceeded those of clay loam soil, with the emergence of a rill when the rainfall intensity was higher. Rills have a much greater effect on sediment concentration and erosion rate for loess soil than for clay loam soil. This study indicates that soil texture has a major impact on rill formation; clay loam soil is more subject to rill formation, but the rills formed are generally small and do not substantially increase soil loss. In contrast, the well‐developed rills in silt loam soil can result in intensive soil loss, though rills occur infrequently. Basic understanding of these results, causes, and quantification are essential for the prediction and evaluation of soil loss.
Lanthanide-doped upconversion nanocrystals (UCNCs) have recently become an attractive nonlinear fluorescence material for use in bioimaging because of their tunable spectral characteristics and ...exceptional photostability. Plasmonic materials are often introduced into the vicinity of UCNCs to increase their emission intensity by means of enlarging the absorption cross-section and accelerating the radiative decay rate. Moreover, plasmonic nanostructures (e.g., gold nanorods, GNRs) can also influence the polarization state of the UC fluorescence--an effect that is of fundamental importance for fluorescence polarization-based imaging methods yet has not been discussed previously. To study this effect, we synthesized GNR@SiO2 @CaF2 :Yb3+ ,Er3+ hybrid core-shell-satellite nanostructures with precise control over the thickness of the SiO2 shell. We evaluated the shell thickness-dependent plasmonic enhancement of the emission intensity in ensemble and studied the plasmonic modulation of the emission polarization at the single-particle level. The hybrid plasmonic UC nanostructures with an optimal shell thickness exhibit an improved bioimaging performance compared with bare UCNCs, and we observed a polarized nature of the light at both UC emission bands, which stems from the relationship between the excitation polarization and GNR orientation. We used electrodynamic simulations combined with Förster resonance energy transfer theory to fully explain the observed effect. Our results provide extensive insights into how the coherent interaction between the emission dipoles of UCNCs and the plasmonic dipoles of the GNR determines the emission polarization state in various situations and thus open the way to the accurate control of the UC emission anisotropy for a wide range of bioimaging and biosensing applications.
African swine fever (ASF)-an aggressive infectious disease caused by the African swine fever virus (ASFV)-is significantly unfavorable for swine production. ASFV has a complex structure and encodes ...150-167 proteins; however, the function of most of these proteins is unknown. This study identified ASFV MGF360-9L as a negative regulator of the interferon (IFN)-β signal. Further evidence showed that MGF360-9L interacts with signal transducer and activator of transcription (STAT) 1 and STAT2 and degrades STAT1 and STAT2 through apoptosis and ubiquitin-proteasome pathways, respectively. Subsequently, the activation of IFN-β signaling was inhibited. Naturally isolated or genetically manipulated live attenuated viruses are known to protect against the virulent parental ASFV strains. Therefore, through homologous recombination, we deleted
from the virulent ASFV CN/GS/2018 strain to construct a recombinant strain, ASFV-Δ360-9L. Compared with the parent ASFV CN/GS/2018 strain, the replication level of ASFV-Δ360-9L decreased in primary porcine alveolar macrophage cultures at 24 h postinfection, but the difference is unlikely to be biologically relevant. Notably, ASFV-Δ360-9L was partially attenuated in pigs. To our knowledge, this study is the first to uncover the function of MGF360-9L during ASFV infection. MGF360-9L inhibits IFN-β signaling through the targeted degradation of STAT1 and STAT2. Furthermore, MGF360-9L is a key virulence gene of ASFV. Our findings reveal a new mechanism by which ASFV inhibits host antiviral response; this might facilitate the development of live attenuated ASFV vaccines.
African swine fever-an acute, febrile, hemorrhagic, highly contacting, and highly lethal disease caused by African swine fever virus (ASFV)-jeopardizes the global pig industry. Understanding the mechanism ASFV employs to evade host defense during infection is essential for developing targeted drugs and vaccines against ASFV. To our knowledge, this study identifies the mechanism of innate immunity against by MGF360-9L and the effect of MGF360-9L on ASFV pathogenicity. The results showed that MGF360-9L may help ASFV escape the host immunity by degrading STAT1 and STAT2 and thus inhibiting IFN-β signaling. MGF360-9L is also an important virulence factor of ASFV. The deletion of
reduces ASFV virulence in pigs. This study explored a new mechanism of ASFV against innate immunity and identified a new ASFV virulence factor; these findings may guide the development of live attenuated ASFV vaccines.
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