Repetition rate tuning and locking of solitons in a microrod resonator.

Recently, there has been significant interest in the generation of coherent temporal solitons in optical microresonators. In this Letter, we present a demonstration of dissipative Kerr soliton generation in a microrod resonator using an auxiliary-laser-assisted thermal response control method. In addition, we are able to control the repetition rate of the soliton over a range of 200 kHz while maintaining the pump laser frequency, by applying external stress tuning. Through the precise control of the PZT voltage, we achieve a stability level of 3.9 × 10-10 for residual fluctuation of the repetition rate when averaged 1 s. Our platform offers precise tuning and locking capabilities for the repetition frequency of coherent mode-locked combs in microresonators. This advancement holds great potential for applications in spectroscopy and precision measurements.

Improving the Laser-Induced Breakdown Spectroscopy for Highly Efficient Trace Measurement of Hazardous Components in Waste Oils.

Improper disposal of waste oils containing hazardous components damages the environment and the ecosystem, posing a significant threat to human life and health. Here, we present a method of discharge-assisted laser-induced breakdown spectroscopy combined with filter paper sampling (DA-LIBS-FPS) to detect hazardous components and trace the source of polluting elements. DA-LIBS-FPS significantly enhances spectral intensity by 1-2 orders of magnitude due to the discharge energy deposition into the laser-induced plasma and the highly efficient laser-sample interaction on the filter paper, when compared to single-pulse LIBS with silica wafer sampling (SP-LIBS-SWS). Additionally, the signal-to-noise ratio and the signal-to-background ratio are both significantly increased. Resultantly, indiscernible lines, such as CN and Cr I, are well distinguished. In contrast with DA-LIBS combined with silica wafer sampling (DA-LIBS-SWS), the spectral signal fluctuations in DA-LIBS-FPS are reduced by up to 33%, because of the homogeneous distribution of the oil layer on the filter paper in FPS. Further examination indicates that the limit of detection for Ba is reduced from a several parts per million level in SP-LIBS-SWS to a dozens of parts per billion level in DA-LIBS-FPS, i.e., nearly 2 orders of magnitude enhancement in analysis sensitivity. This improvement is attributed to the extended plasma lifespan in DA-LIBS and the increasing electron density and plasma temperature in FPS. DA-LIBS-FPS provides a low-cost, handy, rapid, and highly sensitive avenue to analyze the hazardous components in waste oils with great potential in environmental and ecological monitoring.

Routing to mid-infrared microcomb via near-infrared direct pump.

Mid-infrared (MIR) microcomb provides a new way into the "molecular fingerprint" region. However, it remains rather a challenge to realize the broadband mode-locked soliton microcomb, which is often limited by the performance of available MIR pump sources and coupling devices. Here, we propose an effective approach towards broadband MIR soliton microcombs generation via a direct pump in the near-infrared (NIR) region, through full utilization of the second- and third-order nonlinearities in a thin-film lithium niobate microresonator. The optical parametric oscillation process contributes to conversion from the pump at 1550 nm to the signal around 3100 nm, and the four-wave mixing effect promotes spectrum expansion and mode-locking process. While the second-harmonic and sum-frequency generation effects facilitate simultaneous emission of the NIR comb teeth. Both the continuous wave and pulse pump sources with relatively low power can support a MIR soliton with a bandwidth over 600 nm and a concomitant NIR microcomb with a bandwidth of 100 nm. This work can provide a promising solution for broadband MIR microcombs by breaking through the limitation of available MIR pump sources, and can deepen the understanding of the physical mechanism of the quadratic soliton assisted by the Kerr effect.

Micrometer-precision absolute distance measurement with a repetition-rate-locked soliton microcomb.

The soliton microcomb has sparked interest in high-precision distance measurement, owing to its ultrahigh repetition rate and chip-integrated scale. We report absolute distance measurements based on synthetic wavelength interferometry with a soliton microcomb. We stabilized the repetition rate of 48.98 GHz through injection locking, with fluctuations below 0.25 Hz. Distance measurements up to 64 mm were demonstrated, presenting residuals below 2.7 µm compared with a referenced laser interferometer. Long-term distance measurements were made at two fixed positions of approximately 0.2 m and 1.4 m, resulting in a minimum Allan deviation as low as 56.2 nm at an average time of 0.05 s. The dynamic demonstration illustrated that the proposed system could track round-trip motion of 3 mm at speeds up to 100 mm/s. The proposed distance measurement system is, to our knowledge, the first microcomb-based synthetic wavelength interferometer and achieves a ranging precision of tens of nanometers, with potential applications in the fields of satellite formation flying, high-end manufacturing, and micro-nano processing.

Polarization-multiplexed metasurface enabled tri-functional imaging.

Diffraction-limited focusing imaging, edge-enhanced imaging, and long depth of focus imaging offer crucial technical capabilities for applications such as biological microscopy and surface topography detection. To conveniently and quickly realize the microscopy imaging of different functions, the multifunctional integrated system of microscopy imaging has become an increasingly important research direction. However, conventional microscopes necessitate bulky optical components to switch between these functionalities, suffering from the system's complexity and unstability. Hence, solving the problem of integrating multiple functions within an optical system is a pressing need. In this work, we present an approach using a polarization-multiplexed tri-functional metasurface, capable of realizing the aforementioned imaging functions simply by changing the polarization state of the input and output light, enhancing the system structure's compactness and flexibility. This work offers a new avenue for multifunctional imaging, with potential applications in biomedicine and microscopy imaging.

Suppressing grating lobes of large-aperture optical phased array with circular array design.

An optical phased array (OPA), especially a two-dimensional (2D) OPA, suffers from the trade-off among steering range, beam width, and the number of antennas. Aperiodic 2D array designs currently aimed to reduce the number of antennas and reduce grating lobes within a wide range fall short when an aperture approaches millimeter size. A circular OPA design is proposed to address this issue. The circular design substantially reduces the number of antennas while achieving the same wide steering range and narrow beam width of optimized aperiodic 2D OPA designs. Its efficient suppression of grating lobes, the key to a wide steering range with minimal number of antennas and large antenna spacing, is theoretically studied and validated by simulation. The novel, to the best of our knowledge, design allows less than 100 antennas, orders of magnitude reduction, for millimeter size aperture OPA designs. It paves the way for commercialization by significantly reducing control complexity and power consumption.

Hybrid integrated narrow-linewidth semiconductor lasers.

Integrated narrow-linewidth lasers are the key devices in compact coherent optical systems of metrology, sensing, and optical microwave generation. Here, we demonstrate a hybrid integrated laser based on an optical negative feedback scheme. The laser is composed of a commercial distributed feedback (DFB) laser diode and an on-chip micro-resonator with a Q-factor of 0.815 million. The feedback optical field is coupled back to the laser cavity through the back facet. Therefore, the laser can maintain the lasing efficiency of the DFB laser diode. The linewidth of the DFB laser diode is compressed from 2 MHz to 6 kHz, corresponding to the linewidth reduction factor of 25.2 dB. The theoretical result shows that the laser performance still has a huge improvement margin through precise control of the detuning between laser frequency and the micro-resonator, as well as the phase delay of the feedback optical field. The hybrid narrow-linewidth laser diode has wide application prospects in coherent optical systems benefitting from the low cost and volume productivity.

Experimental demonstration of optical trapping and manipulation with multifunctional metasurface.

Chip-scale optical tweezers, which are usually implemented in a planar format without using bulky diffractive optical elements, are recognized as a promising candidate to be integrated with a lab-on-a-chip system. However, traditional chip-scale optical tweezers are often static and allow for only one type of manipulation functionality since the geometrical parameters of the tweezers are fixed. Herein, we introduce a new, to the best of our knowledge, class of on-chip optical tweezers for diverse types of manipulation of micro-particles. Utilizing both the propagation phase and Pancharatnam-Berry phase, we experimentally demonstrate the spin-dependent trapping, moving, and circling of micro-particles with the transfer of optical gradient force and orbital angular momentum to particles. We further show that the spin angular momentum of the output beam provides an additional degree of freedom to control the spinning rotation of particles. This new type of optical tweezers paves the way for multifunctional and dynamical trapping and manipulation of particles with a lab-on-a-chip system.

Mid-infrared optical parametric oscillation spanning 3.4-8.2µm in a MgF2microresonator.

Mid-infrared optical parametric oscillators (OPOs) offer a compelling route for accessing the 'molecular fingerprint' region and, thus, can find intensive applications such as precision spectroscopy and trace gas detection. Yet it still remains rather a challenge to realize broadband mid-infrared OPOs within a single cavity, usually limited by strict phase-matching conditions for wide spectral coverage and available pump power for adequate frequency generation. Here, we report the mid-infrared parametric oscillation spanning from 3.4 to 8.2µm, based on four-wave mixing in a high-QMgF2microresonator with optimized dispersion. The center wavelength at 4.78µm is determined by the continuous tunable quantum cascade laser source, which contributes to effective expansion towards longer wavelength, as well as systemic miniaturization with smaller pump module. Such results could not only shed light on new ultimates of crystal and other microresonators, but also inspire explorations on their growing potentials in near future.

Effective half-wavelength pitch optical phased array design for aliasing-free 2D beam steering.

We present a method to design an optical phased array (OPA) simultaneously realizing both narrow beam width and aliasing-free 2D beam steering without the need to arrange the antennas at actual half-wavelength pitch. The method realizes an effective half-wavelength pitch in one direction formed by location projection of the antennas. The distances between the antennas in the other direction can be sufficiently large to form an effective large aperture realizing narrow beam width without needing a long grating. The presented method is proven by both theory and numerical simulations to achieve an equivalent grating-lobe-free far field of an ordinary half-wavelength pitch design. One design example exhibits 180° steering with a minimal beam width of 0.4° * 0.032° and a sidelobe suppression ratio of >13d B.

Intramolecular Partners in Asymmetric Catalysis Copolymerization: Highly Enantioselective and Controllable at Enhanced Temperatures and Low Loadings.

Asymmetric copolymerization of meso-epoxide and anhydride is a powerful strategy for preparing various isotactic polyesters with two contiguous stereogenic centers. However, the previous binary systems suffered from slow rates at low loadings, poor enantioselectivities and transesterification reactions at enhanced temperatures. Herein, we report novel dinuclear aluminium complexes with multiple chiralities and ammonium salts anchored on ligand frameworks. These bifunctional catalysts exhibit high activities and enantioselectivities for epoxides/anhydrides copolymerizations at harsh conditions via intramolecularly synergistic catalysis, affording polyesters with unprecedented molecular weights and narrow distributions. Notably, no transesterification reactions were observed, significantly different from the binary catalyst/cocatalyst pairs. This study represents a rare example regarding temperature-independent asymmetric induction for preparing chiral polymers from achiral monomers.

Precise dynamic characterization of microcombs assisted by an RF spectrum analyzer with THz bandwidth and MHz resolution.

The radio frequency (RF) spectrum of microcombs can be used to evaluate its phase noise features and coherence between microcomb teeth. Since microcombs possess characteristics such as high repetition rate, narrow linewidth and ultrafast dynamical evolution, there exists strict requirement on the bandwidth, resolution and frame rate of RF measurement system. In this work, a scheme with 1.8-THz bandwidth, 7.5-MHz spectral resolution, and 100-Hz frame rate is presented for RF spectrum measurement of microcombs by using an all-optical RF spectrum analyzer based on cross-phase modulation and Fabry Perot (FP) spectrometer, namely FP-assisted light intensity spectrum analyzer (FP-assisted LISA). However, extra dispersion introduced by amplifying the microcombs will deteriorate the bandwidth performance of measured RF spectrum. After compensating the extra dispersion through monitoring the dispersion curves measured by FP-assisted LISA, the more precise RF spectra of microcombs are measured. Then, the system is used to measure the noise sidebands and line shape evolution of microcombs within 2s temporal window, in which dynamic RF combs variation at different harmonic frequencies up to 1.96 THz in modulation instability (MI) state and soliton state are recorded firstly. Therefore, the improved bandwidth and resolution of FP-assisted LISA enable more precise measurement of RF spectrum, paving a reliable way for researches on physical mechanism of microcombs.

Demonstration of an external cavity semiconductor mode-locked laser.

Electrically pumped semiconductor mode-locked lasers (SMLs) are promising in a wide range of applications due to compact size, high energy efficiency, and low cost. However, the long gain interaction length increases the spontaneous emission noise. In this Letter, an external cavity structure is adopted to improve the SML noise performance, as well as the flexibility to adjust the repetition rate. Two external cavity SMLs with repetition rates of 255 MHz and 10 GHz are demonstrated. For the 10 GHz SML, the signal-noise-ratio and radio frequency linewidth of the fundamental frequency reach 81.1 dB and 40 Hz, respectively. The high performance makes the laser a promising light source for microwave and communication applications.

Nonlinear calibration of frequency modulated continuous wave LIDAR based on a microresonator soliton comb.

Traditional frequency modulated continuous wave (FMCW) LIDAR ranging is based on heterodyne detection, calculating unknown distance by extracting the frequency of the interference signal, while the main error source is frequency modulation (FM) nonlinearity. In this paper, a ranging system based on a microresonator soliton comb is demonstrated to correct the nonlinearity by sampling the ranging signals at equal frequency intervals, producing a ranging error lower than 20 µm, while at the range of 2 m. Advantages of fast data acquisition, light computation requirements, and a simple optical path, without long optical fiber, give this method a high practical value in precision manufacturing.

On the modelling of tropical tree growth: the importance of intra-specific trait variation, non-linear functions and phenotypic integration.

BACKGROUND AND AIMS: The composition and dynamics of plant communities arise from individual-level demographic outcomes, which are driven by interactions between phenotypes and the environment. Functional traits that can be measured across plants are frequently used to model plant growth and survival. Perhaps surprisingly, species average trait values are often used in these studies and, in some cases, these trait values come from other regions or averages calculated from global databases. This data aggregation potentially results in a large loss of valuable information that probably results in models of plant performance that are weak or even misleading. METHODS: We present individual-level trait and fine-scale growth data from >500 co-occurring individual trees from 20 species in a Chinese tropical rain forest. We construct Bayesian models of growth informed by theory and construct hierarchical Bayesian models that utilize both individual- and species-level trait data, and compare these models with models only using individual-level data. KEY RESULTS: We show that trait-growth relationships measured at the individual level vary across species, are often weak using commonly measured traits and do not align with the results of analyses conducted at the species level. However, when we construct individual-level models of growth using leaf area ratio approximations and integrated phenotypes, we generated strong predictive models of tree growth. CONCLUSIONS: Here, we have shown that individual-level models of tree growth that are built using integrative traits always outperform individual-level models of tree growth that use commonly measured traits. Furthermore, individual-level models, generally, do not support the findings of trait-growth relationships quantified at the species level. This indicates that aggregating trait and growth data to the species level results in poorer and probably misleading models of how traits are related to tree performance.

Compact 2D serpentine optical phased array.

We present a two-dimensional (2D) Si photonics optical phased array (OPA) using a serpentine design which eliminates the long directional couplers used in many 2D OPA designs. It significantly reduces the distance between the antenna benefitting far-field sidelobe reduction while maintaining high optical power use efficiency.

Conspecific negative density dependence in rainy season enhanced seedling diversity across habitats in a tropical forest.

Conspecific negative density dependence (CNDD) could be one of the most important local-scale mechanisms shaping plant species coexistence. However, the spatial and temporal changes in the strength CNDD and the implications for the plant diversity remain unknown. We used 10 years of seedling data, in a seasonal tropical rainforest, to discover how CNDD influences tree seedling survival across habitats and seasons. We also evaluated the relation between CNDD and species diversity. We found the strength of CNDD in the valley habitat was significantly stronger than in ridge habitat in rainy season, but not significantly different in dry season. Corresponding to expectations of CNDD as mechanism of diversity maintenance, seedling species diversity was significantly higher in valley habitat than in ridge habitat and significantly correlated with CNDD. Additionally, conspecific and heterospecific seedling neighbour densities positively affected the survival of tree seedlings, but heterospecific adult neighbour density had a weak effect. Our study finds that CNDD varied significantly across habitats and was correlated with local seedling diversity. Our results highlight the importance of CNDD in driving species diversity at the local scale. Recognizing the spatial and temporal variation in the strength of CNDD will aid efforts to model and understand species coexistence.

Impact of third-order dispersion and three-photon absorption on mid-infrared time magnification via four-wave mixing in Si0.8Ge0.2 waveguides.

We investigate the influence of third-order dispersion of dispersive elements, three-photon absorption and free-carrier effects on mid-infrared time magnification via four-wave mixing (FWM) in ${{\rm Si}_{0.8}}{{\rm Ge}_{0.2}}$Si0.8Ge0.2 waveguides. It is found that the magnified waveform is seriously distorted by these factors, and conversion efficiency is decreased, mainly because of nonlinear absorption. A time lens based on FWM in ${{\rm Si}_{0.8}}{{\rm Ge}_{0.2}}$Si0.8Ge0.2 waveguides is proposed for time magnification of mid-infrared ultrashort pulses, in which the low-distortion, high-magnification in the time domain could be obtained by optimizing system parameters. These results make it possible to analyze the transient dynamic process through oscilloscopes and detectors with gigahertz bandwidth and have important applications in ultrafast process analysis, optical pulse sampling, and optical communications.

Comprehensive characterization of immune- and inflammation-associated biomarkers based on multi-omics integration in kidney renal clear cell carcinoma.

BACKGROUND: Kidney renal clear cell carcinoma (KIRC) is the most common type of kidney cancer in adults, and it is responsible for approximately 90-95% of cases. Although extensive evidence has suggested that many immune- and inflammation-related genes could serve as effective biomarkers in KIRC, the potential associations among immune-, inflammation- and KIRC-related genes has not been sufficiently understood. METHODS: Here, we integrated multiple levels of data to construct an immune-, inflammation- or KIRC-directed neighbour network (IIKDN network) and a KIRC-related gene-directed network (KIRCD network). RESULTS: Our analysis suggested that immune- and inflammation-related genes in the network have special topological characteristics and expression patterns related to KIRC. We further identified five core clusters that showed a tighter network structure and stronger correlation of expression from the KIRCD network. Specifically, multiple-level molecular characteristics were systematically portrayed, including somatic mutation, copy-number variant and DNA methylation for the genes in five core clusters. We discovered that the genes showed strong correlation with respect to the expression and methylation levels in these five core clusters. These five core clusters could become special prognostic biomarkers for KIRC, and functional analysis showed that they were associated with activation of the immune and inflammation systems and cancer progression. CONCLUSIONS: Our findings highlighted the novel role of the immune and inflammation genes in KIRC.

Influences of high-order dispersion on temporal and spectral properties of microcavity solitons.

We theoretically and numerically investigate the effects of high-order dispersion (HOD) on microcavity solitons, both in time and frequency domain with an extended normalized Lugiato-Lefever equation (LLE). The observed temporal drift of bright and dark solitons is shown to originate from high-odd-order dispersion, while the sign determines the direction of soliton movement and the amplitude decides the drift speed. HOD can also be introduced to stabilize the breathing bright and dark cavity solitons. In spectral domain, the nonlinear symmetry breaking is mainly introduced by third-order dispersion, whereas both third- and fourth-order dispersion can introduce dispersive wave accompanied by soliton tail oscillation. This work could give insight for exploring detailed intracavity pulse dynamics and spectral characteristics of Kerr combs influenced by HOD, as well as provide a viable route to delicate control of Kerr comb generation through tailoring the dispersion parameters.