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Vascular stenosis caused by atherosclerosis instigates activation and aggregation of platelets, eventually resulting in thrombus formation. Although antiplatelet drugs are commonly used to inhibit platelet activation and aggregation, they unfortunately cannot prevent recurrent thrombotic events in patients with atherosclerosis. This is partially due to the limited understanding of the efficacy of antiplatelet drugs in the complex hemodynamic environment of vascular stenosis. Conventional methods for evaluating the efficacy of antiplatelet drugs under stenosis either fail to simulate the hemodynamic environment of vascular stenosis characterized by high shear stress and recirculatory flow or lack spatial resolution in their analytical techniques to statistically identify and characterize platelet aggregates. Here we propose and experimentally demonstrate a method comprising an

Technological advances in image-based platelet analysis or platelet morphometry are critical for a better understanding of the structure and function of platelets in biological research as well as for the development of better clinical strategies in medical practice. Recently, the advent of high-throughput optical imaging and deep learning has boosted platelet morphometry to the next level by providing a new set of capabilities beyond what is achievable with traditional platelet morphometry, shedding light on the unexplored domain of platelet analysis. This Opinion article introduces emerging opportunities in 'intelligent' platelet morphometry, which are expected to pave the way for a new class of diagnostics, pharmacometrics, and therapeutics.

Microvascular thrombosis is a typical symptom of COVID-19 and shows similarities to thrombosis. Using a microfluidic imaging flow cytometer, we measured the blood of 181 COVID-19 samples and 101 non-COVID-19 thrombosis samples, resulting in a total of 6.3 million bright-field images. We trained a convolutional neural network to distinguish single platelets, platelet aggregates, and white blood cells and performed classical image analysis for each subpopulation individually. Based on derived single-cell features for each population, we trained machine learning models for classification between COVID-19 and non-COVID-19 thrombosis, resulting in a patient testing accuracy of 75%. This result indicates that platelet formation differs between COVID-19 and non-COVID-19 thrombosis. All analysis steps were optimized for efficiency and implemented in an easy-to-use plugin for the image viewer napari, allowing the entire analysis to be performed within seconds on mid-range computers, which could be used for real-time diagnosis.

There is a global concern about the safety of COVID-19 vaccines associated with platelet function. However, their long-term effects on overall platelet activity remain poorly understood. Here we address this problem by image-based single-cell profiling and temporal monitoring of circulating platelet aggregates in the blood of healthy human subjects, before and after they received multiple Pfizer-BioNTech (BNT162b2) vaccine doses over a time span of nearly 1 year. Results show no significant or persisting platelet aggregation trends following the vaccine doses, indicating that any effects of vaccinations on platelet turnover, platelet activation, platelet aggregation, and platelet-leukocyte interaction was insignificant.

Raman optical activity (ROA) is effective for studying the conformational structure and behavior of chiral molecules in aqueous solutions and is advantageous over X-ray crystallography and nuclear magnetic resonance spectroscopy in sample preparation and cost performance. However, ROA signals are inherently minuscule; 3–5 orders of magnitude weaker than spontaneous Raman scattering due to the weak chiral light–matter interaction. Localized surface plasmon resonance on metallic nanoparticles has been employed to enhance ROA signals, but suffers from detrimental spectral artifacts due to its photothermal heat generation and inability to efficiently transfer and enhance optical chirality from the far field to the near field. Here we demonstrate all-dielectric chiral-field-enhanced ROA by devising a silicon nanodisk array and exploiting its dark mode to overcome these limitations. Specifically, we use it with pairs of chemical and biological enantiomers to show >100x enhanced chiral light–molecule interaction with negligible artifacts for ROA measurements., Raman optical activity (ROA) is useful for studying conformational structure and behavior of chiral molecules, but is limited by the weak signals. Here, the authors demonstrate 100x signal enhancement via an all-dielectric approach, using a silicon nanodisk array and exploiting its dark mode.

Mid-infrared (Mid-IR) Kerr frequency combs have great application potential in sensing and spectroscopy. To generate a Kerr frequency comb, a continuous-wave, wavelength-tunable, narrow-linewidth, low-noise laser is normally utilized to pump a high-nonlinearity micro-resonator to emit a large number of coherent and equally spaced modes. However, chip-based pump lasers in the mid-IR band, namely, quantum cascade lasers and interband cascade lasers, are usually challenging to develop with both high output powers and good wavelength tunability based on a single diode. To overcome the limitation, we theoretically study a mid-IR Kerr frequency comb generation technique based on a graphene-on-silicon micro-resonator by using a monochromatic mid-IR laser. The approach is based on the exploration of an electric-field-assisted resonance scanning technique and graphene-enhanced silicon Kerr nonlinearity. Our result shows that a soliton Kerr frequency comb with a spectral range of 3.23–5.26 μm, 3-dB bandwidth of ∼550 nm, and frequency spacing of 140 GHz could be generated under a pump wavelength of 4 μm. The study paves a promising way toward developing monolithically chip-integrated mid-IR Kerr frequency combs with cost efficiencies and ultrafast tuning speeds.

Fiber-optic sensors are an indispensable element of modern sensing technologies by virtue of their low cost, excellent electromagnetic immunity, and remote sensing capability. Optical Vernier effect is widely used to enhance sensitivity of fiber-optic sensors but requires bulky and complex cascaded interferometers. Here we propose and experimentally demonstrate an ultracompact (∼2 mm by ∼2 mm) Vernier-effect-improved sensor by only using a single microfiber-knot resonator. With the Vernier effect achieved by controlling the optical beating with the spectral ripple of a super light emitting diode (SLED), we show ∼20x sensitivity enhancement for quantitative temperature monitoring. Our sensor creates a new practical method to realize Vernier effect in fiber-optic sensors and beyond.

Transition metal dichalcogenides (TMDs), as one of the most promising two-dimensional (2D) materials, have attracted considerable attention for use in photodetection applications over the past few years due to their distinct properties, such as atomic-scale thickness, tunable direct bandgaps, and decent carrier mobilities at room temperature. Compared with pure 2D TMDs, the construction of hybrids consisting of TMDs and other low-dimensional materials can further improve the performance of photodetectors including their spectral range, responsivity and detectivity, which significantly boosts interest in the development of TMDs-based photodetectors. On the other hand, solution-phase synthesis methods provide a facile strategy for the scalable production of TMD hybrids, opening an exciting avenue to develop low-cost devices. In this review, we summarize the material synthesis, characterizations, and photodetection applications of the solution processable TMDs-based hybrids, as well as provide insights into their prospects.

Sepsis is a life-threatening condition caused by the extreme release of inflammatory mediators into the blood in response to infection (e.g., bacterial infection, COVID-19), resulting in the dysfunction of multiple organs. Currently, there is no direct treatment for sepsis. Here we report an abiotic hydrogel nanoparticle (HNP) as a potential therapeutic agent for late-stage sepsis. The HNP captures and neutralizes all variants of histones, a major inflammatory mediator released during sepsis. The highly optimized HNP has high capacity and long-term circulation capability for the selective sequestration and neutralization of histones. Intravenous injection of the HNP protects mice against a lethal dose of histones through the inhibition of platelet aggregation and migration into the lungs. In vivo administration in murine sepsis model mice results in near complete survival. These results establish the potential for synthetic, nonbiological polymer hydrogel sequestrants as a new intervention strategy for sepsis therapy and adds to our understanding of the importance of histones to this condition., Sepsis caused by the release of inflammatory mediators into the blood is a life threatening disease. Here, the authors report on the development of hydrogel nanoparticles for the capture and neutralisation of histones, major inflammatory mediators, and demonstrate sepsis treatment in a murine model.

Graphene oxide (GO) or reduced-GO offer excellent mechanical, electrical and chemical properties. Their nanocomposites have been increasingly explored for attractive applications in diverse fields. However, due to the flexible feature and weak interlayer interactions of GO sheets, flexural mechanical properties of GO-based composites especially for the bulk materials are largely restrained, which would hinder their use in real situations. Here inspired by amorphous/crystalline heterophase features within nacreous platelets, we construct a centimetre-sized GO-based bulk, the building blocks of which consist of crystalline GO and amorphous/crystalline MnO2 phases adhered by polymer-based crosslinkers. The GO/MnO2 heterophase layers are stacked and hot-pressed with further crosslinking between the layers to form bulk artificial nacre. The resultant GO/MnO2-based layered (GML) bulk exhibits the highest flexural strength (up to 203.4 MPa) among all of GO-based bulk materials. Moreover, an excellent fracture toughness, a strong impact resistance and light weight are also achieved. Mechanical and simulation analyses corroborate that the highly ordered heterophase structure together with complex crosslinking interactions across multiscale interfaces, lead to superior mechanical properties. We expect that these results provide interesting insights into the design of structural materials and allow the use of high-performance GO-based bulks in engineering and military applications.

Graphene oxide (GO) and reduced GO possess robust mechanical, electrical and chemical properties. Their nanocomposites have been extensively explored for applications in diverse fields. However, due to the high flexibility and weak interlayer interactions of GO nanosheets, the flexural mechanical properties of GO-based composites, especially in bulk materials, are largely constrained, which hinders their performance in practical applications. Here, inspired by the amorphous/crystalline feature of the heterophase within nacreous platelets, we present a centimetre-sized, GO-based bulk material consisting of building blocks of GO and amorphous/crystalline leaf-like MnO

A characteristic clinical feature of COVID-19 is the frequent incidence of microvascular thrombosis. In fact, COVID-19 autopsy reports have shown widespread thrombotic microangiopathy characterized by extensive diffuse microthrombi within peripheral capillaries and arterioles in lungs, hearts, and other organs, resulting in multiorgan failure. However, the underlying process of COVID-19-associated microvascular thrombosis remains elusive due to the lack of tools to statistically examine platelet aggregation (i.e., the initiation of microthrombus formation) in detail. Here we present a method for massive image-based profiling, temporal monitoring, and big data analysis of circulating platelets and platelet aggregates in the blood of COVID-19 patients at single-cell resolution, to provide previously unattainable insights into the disease. In fact, our analysis of the image data from 110 hospitalized patients shows the anomalous presence of excessive platelet aggregates in nearly 90% of all COVID-19 patients. Furthermore, results indicate strong links between the concentration of platelet aggregates and the severity, mortality, and respiratory condition of patients with COVID-19. Finally, high-dimensional analysis based on deep learning shows that the disease behaves as systemic thrombosis.

A characteristic clinical feature of COVID-19 is the frequent occurrence of thrombotic events. Furthermore, many cases of multiorgan failure are thrombotic in nature. Since the outbreak of COVID-19, D-dimer testing has been used extensively to evaluate COVID-19-associated thrombosis, but does not provide a complete view of the disease because it probes blood coagulation, but not platelet activity. Due to this limitation, D-dimer testing fails to account for thrombotic events which occur despite low D-dimer levels, such as sudden stroke in young patients and autopsy-identified widespread microthrombi in multiple organs. Here we report the landscape of circulating platelet aggregates in COVID-19 obtained by large-scale single-cell image-based profiling and temporal monitoring of the blood of COVID-19 patients (n = 110). Surprisingly, our analysis shows the anomalous presence of excessive platelet aggregates in nearly 90% of all COVID-19 patients, including those who were not clinically diagnosed with thrombosis and those with low D-dimer levels (≤1 µg/mL). Additionally, results indicate a strong link between the concentration of platelet aggregates and the severity and mortality of COVID-19. Finally, high-dimensional analysis and comparison with other diseases reveal that COVID-19 behaves as a product of thrombosis (localized) and infectious diseases (systemic), as a cause of systemic thrombosis.

In COVID-19 therapy with artificial lungs such as extracorporeal membrane oxygenation (ECMO) machines, platelets in the extracorporeal circulation are often activated by their contact with the artificial materials, leading to the formation of blood clots followed by serious complications such as stroke and heart attack. However, anticoagulation and antithrombotic management is challenging due to the lack of testing tools to evaluate the circulation. Here we demonstrate real-time monitoring of thrombogenesis in the circulation of an ECMO-equipped goat with an intelligent platelet aggregate characterizer (iPAC), which is based on imaging flow cytometry and deep-learning-based analysis of numerous platelet aggregates in blood.

Positioning a single quantum emitter in the vicinity of a plasmonic antenna is a fundamental step in constructing a coupling system for quantum information applications. In the strong-coupling regime, optical forces beyond perturbative Rayleigh gradient forces are dominant in positioning and trapping the quantum emitter but are rarely explored by including the electronic contribution of the quantum emitter. Here we study the optical forces induced by the strong exciton-plasmon coupling between a single quantum dot and a plasmonic nanoantenna. Interestingly, both attractive and repulsive optical forces can be generated, which are fully controllable and tunable by engineering both excitons and plasmons.

In the recent years, the emergence of metal-free surface-enhanced Raman scattering (SERS) substrates has provided promising alternatives for reliable, high-sensitivity Raman spectroscopy due to their potential to realize highly tuneable, biocompatible, and reproducible Raman enhancement. In this perspective article, we discuss recent developments and anticipate new opportunities for metal-free SERS. Specifically, we review the theory of metal-free SERS, including electromagnetic enhancement and chemical enhancement, and introduce promising substrates developed recently, including MXenes, transition metal dichalcogenides, and carbon-based substrates. Moreover, we clarify challenges, provide potential solutions, and discuss unexploited applications. This perspective provides not only a broad and detailed view of metal-free SERS at the current stage, but also a roadmap for its future advancement.

The chiroptical effect is a property that describes distinct response of matter to light with opposite handedness, which is extensively utilized in stereochemistry, analytical chemistry, metamaterials, and spin photonics. Conventionally, metallic nanostructures have been harnessed to generate a strong chiroptical effect with the assistance of surface plasmon resonance, but they usually suffer from low energy efficiency and large photothermal heat generation due to the high ohmic loss of metallic materials, which severely restricts their practical applications. Here we present a dielectric spiral nanoflower with a giant chiroptical effect produced by magnetic resonance. We theoretically predicted the giant chiroptical effect of the spiral nanoflower by numerical simulations and analyzed its underlying physics by combination of a multipole expansion method. Based on the theoretical design, we experimentally fabricated the spiral nanoflower and demonstrated its strong chiroptical effect by characterizing its circular intensity difference (CID). The largest-to-date CID of 35% is demonstrated. The magnetic quadrupole interference within the spiral nanoflower was also clarified by experimentally tailoring its magnetic quadrupole interference. Our work is expected to overcome the limitation of conventional metallic platforms and pave the way toward the development of various highly efficient and thermostable chiroptical devices and applications.

Optical assembly as a multiple optical trapping technique enables patterned arrangements of matter ranging from atoms to microparticles for diverse applications in biophysics, quantum physics, surface chemistry, and cell biology. Optical potential energy landscapes based on evanescent fields are conventionally employed for optical assembly of subwavelength particles, but are typically limited to predefined patterns and lacking in tunability. Here we present a microfiber photonic crystal cavity applicable for tunable optical assembly of subwavelength particles along a flexible path. This is enabled by excellent mechanical flexibility of the microfiber cavity as well as its broadband photonic crystal reflectors. By virtue of the broadband reflectors, the lattice constant of the assembled particles is precisely tunable via altering the wavelength of input light. Three-dimensional optical assembly is also realized by making use of the high-order transverse mode of the microfiber cavity. Moreover, the optical assembly process is detectable by simply monitoring the reflection/transmission spectrum of the microfiber cavity. The design of the microfiber cavity heralds a new way for tunable optical assembly of subwavelength particles, potentially applicable for development of tunable photonic crystals, metamaterials, and sensors.

Mid-infrared (MIR) resonators with high quality (Q) factors play crucial roles in a variety of applications in nonlinear optics, lasing, biochemical sensing, and spectroscopy by virtue of their features of long photon lifetime as well as strong field confinement and enhancement. Previously, such devices have been mainly studied on silicon integration platforms while the development of high-Q germanium resonators is still in its infancy due to quality limitations of current germanium integration platforms. Compared with silicon, germanium possesses a number of advantages for MIR applications, such as a wider transparency window (2 - 15 µm), a higher refractive index (~4), and a higher third-order nonlinear susceptibility. Here we present our experimental demonstration of two types of MIR high-Q germanium resonators, namely, a microring resonator and a photonic crystal nanobeam cavity. A maximum Q factor of ~57,000 is experimentally realized, which is the highest to date on germanium platforms. Moreover, we demonstrate a monolithic integration of the high-Q germanium resonators with suspended-membrane waveguides and focusing subwavelength grating couplers. Our resonators pave a new avenue for the study of on-chip light-germanium interactions and development of on-chip MIR applications in sensing and spectroscopy.

In the near future, single-molecule surface-enhanced Raman spectroscopy (SERS) is expected to expand the family of popular analytical tools for single-molecule characterization. We provide a roadmap for achieving single molecule SERS through different enhancement strategies for diverse applications. We introduce some characteristic features related to single-molecule SERS, such as Raman enhancement factor, intensity fluctuation, and data analysis. We then review recent strategies for enhancing the Raman signal intensities of single molecules, including electromagnetic enhancement, chemical enhancement, and resonance enhancement strategies. To demonstrate the utility of single-molecule SERS in practical applications, we present several examples of its use in various fields, including catalysis, imaging, and nanoelectronics. Finally, we specify current challenges in the development of single-molecule SERS and propose corresponding solutions.

We passively mode locked a fiber laser using SiN waveguides covered with graphene of different lengths, and observed two types of solitons, with single and multiple pulses. Grating couplers induce NPR, but graphene triggers mode-locking.

The combination of graphene and a silicon photonic crystal cavity provides an ideal structure for realizing sensitive all-optical modulation. In this paper, an all-optical tuning of a graphene-cladded photonic crystal cavity is demonstrated. A 3.5 nm resonance wavelength shift and a 20% quality factor change are observed as a 1064 nm continuous-wave control laser is focused on the cavity. The resonance wavelength shift is nearly 2 times that realized with electrical modulation and can be further improved with increasing laser power. Meanwhile, it is found that the laser power to reach the saturation absorption state of graphene is nearly 2 orders of magnitude lower than that for monolayer graphene on silica. The experimental results are attributed to optically induced transparency and hot carrier effects. This study opens up a promising way to construct a sensitive all-optical modulator, which is a necessary device in an all-optical integrated circuit, by using a graphene-cladded photonic crystal cavity.

We report the development of an isocyanide-based molecular probe for in situ characterizing the overgrowth of a second metal on silver nanocrystal seeds in solution by surface-enhanced Raman scattering (SERS). As the first demonstration, we elucidate that the vibrational frequency of 2,6-dimethylphenyl isocyanide (2,6-DMPI) can serve as a distinctive reporter for capturing the nucleation of Pt on the edges of Ag nanocubes in the aqueous solution containing a Pt precursor, ascorbic acid, and poly(vinylpyrrolidone) under ambient conditions. Our success relies on the difference in stretching frequency for the NC bond when the isocyanide group binds to the Ag and Pt atoms. Specifically, σ donation from the antibonding σ* orbital of the -NC group to the d-band of Ag would strengthen the NC bond, blue shifting the stretching frequency. In contrast, π-back-donation from the d-band of Pt to the π* antibonding orbital of the -NC group would weaken the NC bond, leading to a red shift of stretching frequency. Therefore, it is feasible to in situ characterize the outermost surface that consists of both newly deposited Pt atoms and remaining Ag atoms by following the stretching frequencies and intensities of 2,6-DMPI in real time. Because the SERS hot spots on the edges of Ag nanocubes coincide with the {110} facets preferred for the nucleation of Pt atoms, this technique is capable of resolving 27 Pt atoms being deposited on each edge of a 39 nm Ag nanocube in the original growth solution. Collectively, in situ SERS, with its consummate sensitivity to molecular structure and bonding of isocyanide-based molecular probe, could elucidate the mechanistic details involved in the seeded overgrowth of a catalytically significant metal, such as Pt, Pd, Ir, Rh, and Ru, on the surface of a Ag or Au nanocrystal seed.

Objective: Oxidative stress plays a critical role in the development of osteoporosis. Hydrogen sulfide (H2S), produces anti-oxidant effect in various biological systems. The present study found that GYY4137, a slow H2S releasing compound, stimulated both mRNA level and activity of alkaline phosphatase, the marker of osteoblast differentiation. This research aims to explore the mechanism on how GYY4137 stimulates osteoblastic cell proliferation and differentiation via an ERK1/2-dependent anti-oxidant approach. Methods: The MC3T3-E1 osteoblast-like cell line was cultured in plate. After pretreatment with GYY4137 (100 µM) for 30 min, the cells were washed twice with PBS solution and then incubated in freshly prepared low serum medium containing 400 μM H2O2 for 4 h. Cells viability was evaluated with the MTT. Cell apoptosis was evaluated by the Hoechst 33342. Then, ALP activity, NO and the superoxide dismutase (SOD) activity is determined by assay kit accordingly, ALP mRNA is identified by RT-PCR. ERK1/2 was analyzed by Western blot. The ROS production was measured with a fluorescence reader. All data was analyzed by SPSS 16.0. Results: We found in the present study that GYY4137, a slow H2S releasing compound, stimulated both mRNA level and activity of alkaline phosphatase, the marker of osteoblast differentiation. RT-PCR shows that GYY4137 stimulated the transcriptional levels of Runx2, a key transcription factor associated with osteoblast differentiation. These data suggest that GYY4137 may stimulate osteoblastic cell proliferation and differentiation. Moreover, GYY4137, which alone at 1-1000 µM had no significant effect, protected MC3T3-E1 osteoblastic cells against hydrogen peroxide (H2O2)-induced cell death and apoptosis. This was mediated by its anti-oxidant effect, as GYY4137 reversed the reduced superoxide dismutase activity and the elevated productions of reactive oxygen species and nitric oxide in the osteoblastic cells treated with H2O2. Western blotting analysis showed that the protective effects of GYY4137 were mediated by suppression of ERK1/2. Conclusions: GYY4137 stimulates osteoblastic cell proliferation and bone differentiation via an ERK1/2-dependent anti-oxidant mechanism. Our findings suggest that GYY4137 may have a potentially therapeutic value for osteoporosis.

Surface plasmon polaritons (SPPs) manipulation is of vital importance to construct ultracompact integrated micro/nano-optical devices and systems. Here we report the design, fabrication and characterization of a SPP microcavity with full transverse and longitudinal mode selection and control on the surface of gold film. The designed microcavity supports the fundamental and first-order transverse modes of Gaussian mode beam with controllable longitudinal modes, respectively. The transverse mode is determined by two holographic mirrors made from deliberately designed groove patterns via the surface electromagnetic wave holography methodology, while the longitudinal mode is determined by the length of cavity. Both numerical simulations and leaky-wave SPP mode observations confirm the realization of full mode selection in the fabricated cavity. Our work opens up a powerful way to fully explore longitudinal and transverse mode control in SPP microcavities, which will be beneficial for light-matter interaction enhancement, construction of novel SPP nanolaser and microlaser, optical sensing and optical information processing.

In this paper, we report our results on the use of patterned graphene on SiN waveguides inside an erbium doped fiber ring laser cavity for passive mode locking. We confirm the dominant influence of graphene over non-linear polarization rotation (NPR), arising from polarizing fiber to chip grating couplers, by observing the limits of NPR in high cavity loss fiber lasers. We fabricated waveguides, transferred and patterned graphene to three different lengths, and observed different types of pulses based on the length of graphene, pump power and polarization state of the cavity. We confirmed the success of graphene processing through Raman scattering and saturable absorption measurements, as well graphene absorption simulation. High chip-coupling loss was overcome by using multiple erbium-doped fiber amplifiers. We believe this research will stimulate further interest in combining integrated photonics and fiber laser technologies, and the miniaturization of pulsed laser cavities.

Mid-infrared (MIR) integrated photonics has attracted broad interest due to its promising applications in biochemical sensing, environmental monitoring, disease diagnosis, and optical communication. Among MIR integration platforms, germanium-based platforms hold many excellent properties, such as wide transparency windows, high refractive indices, and high nonlinear coefficients; however, the development of MIR germanium photonic devices is still in its infancy. Specifically, MIR high-Q germanium resonators with comparable performance to their silicon counterparts remain unprecedented. Here we experimentally demonstrate an MIR germanium nanocavity with a Q factor of ∼18,000, the highest-to-date of reported nanocavities across MIR germanium-based integration platforms. This is achieved through a combination of a feasible theoretical design, Smart-Cut methods for wafer development, and optimized device fabrication processes. Our nanocavity, with its high Q factor and ultrasmall mode volume, opens new avenues for on-chip applications in the MIR spectral range.

Optical activity is an effect of prominent importance in stereochemistry, analytical chemistry, metamaterials, spin photonics, and astrobiology, but is naturally minuscule. Metallic nanostructures are commonly exploited as basic elements for artificially producing large optical activity by virtue of surface plasmon resonance (SPR) on the nanostructures. However, their intrinsic high ohmic loss amplified by the SPR results in low energy efficiency and large photothermal heat generation, severely limiting their performance and practical utility. Giant optical activity by inducing magnetic resonance in an all-dielectric spiral nanoflower (spiral-flower-shaped nanostructure) is demonstrated here. Specifically, a large circular-intensity difference of ≈35% is theoretically predicted and experimentally demonstrated by optimizing the magnetic quadrupole contribution of the nanoflower to scattered light. The nanoflower overcomes the bottleneck of the traditional metallic platforms and enables the development of diverse chiroptical devices and applications.

The mid-infrared (MIR) spectral range holds significant potential for spectroscopic and sensing applications because it encompasses the fingerprint region that unveils the vibrational and rotational signatures of molecules. CMOS-compatible on-chip devices that can achieve strong light-matter interaction in the entire fingerprint region are considered a promising way for such applications, but remain unprecedented. Here we present an on-chip MIR germanium photonic crystal cavity that covers the entire fingerprint region. This is made possible by harnessing a homemade air-cladding germanium platform. Our MIR device creates a new avenue toward integrated nonlinear optics and on-chip biochemical sensing in the fingerprint region.

We present a focusing subwavelength grating (SWG) for efficient coupling of mid-infrared (mid-IR) light into suspended membrane Ge photonic integrated circuits (PICs) that enable mid-IR applications in the entire fingerprint region. By virtue of their wide spectral transparency window and air-cladding device configuration, the suspended membrane Ge PICs are expected to be effective for mid-IR applications over the spectral region covering from 2 to 15 μm. Specifically, we demonstrate the maximum coupling efficiency of -11 dB with a 1-dB bandwidth of ∼58 nm at the SWG's center wavelength of 2.37 μm. Our focusing SWG is expected to advance the development of on-chip long-wavelength mid-IR applications such as biochemical sensing, thermal imaging, and nonlinear optics in the fingerprint region.

Graphene surface plasmons (GSPs) have shown great potential in biochemical sensing, thermal imaging, and optoelectronics. To excite GSPs, several methods based on the near-field optical microscope and graphene nanostructures have been developed in the past few years. However, these methods suffer from their bulky setups and low GSP-excitation efficiency due to the short interaction length between free-space vertical excitation light and the atomic layer of graphene. Here we present a CMOS-compatible design of graphene-on-silicon hybrid plasmonic-photonic integrated circuits that achieve the in-plane excitation of GSP polaritons as well as localized surface plasmon (SP) resonance. By employing a suspended membrane slot waveguide, our design is able to excite GSP polaritons on a chip. Moreover, by utilizing a graphene nanoribbon array, we engineer the transmission spectrum of the waveguide by excitation of localized SP resonance. Our theoretical and computational study paves a new avenue to enable, modulate, and monitor GSPs on a chip, potentially applicable for the development of on-chip electro-optic devices.

Light-beam-splitting characteristics are theoretically and experimentally studied in 2D square-lattice photonic crystals (PhCs) with delicately designed and modulated output surfaces. Compared with the traditional branch-waveguide and self-collimation-type PhC splitters, our proposed structure can not only split the input light beam into different numbers of branches but also realize the adjustment of their relative light intensities in each branch. Moreover, the influence of a light beam's incident angle on both the output branch beams' relative intensity and propagation direction is investigated. This proposed light beam splitter is able to work within a broad frequency range, and the propagation directions of the output split beams can be modified with the incident beam's frequency. In addition, when the PhC device becomes thicker, a kind of light-beam-focusing phenomenon is observed. Advantageously, our light-beam-splitting device has no restriction as to the incident light beam's location and width, so it is much more convenient and practical for achieving optical connection with other functional devices in complicated, large-scale, all-optical integrated circuits.