Exceptional-point-enhanced sensing in an all-fiber bending sensor

An exceptional-point(EP)enhanced fiber-optic bending sensor is reported.The sensor is implemented based on paritytime(PT)-symmetry using two coupled Fabry-Perot(FP)resonators consisting of three cascaded fiber Bragg gratings(FBGs)inscribed in an erbium-ytterbium co-doped fiber(EYDF).The EP is achieved by controlling the pumping power to manipulate the gain and loss of the gain and loss FP resonators.Once a bending force is applied to the gain FP resonator to make the operation of the system away from its EP,frequency splitting occurs,and the frequency spacing is a nonlinear function of the bending curvature,with an increased slope near the EP.Thus,by measuring the frequency spacing,the bending information is measured with increased sensitivity.To achieve high-speed and high-resolution interrogation,the optical spectral response of the sensor is converted to the microwave domain by implementing a dual-passband microwave-photonic filter(MPF),with the spacing between the two passbands equal to that of the frequency splitting.The proposed sensor is evaluated experimentally.A curvature sensing range from 0.28 to 2.74 m^(−1) is achieved with an accuracy of 7.56×10^(−4 )m^(−1 )and a sensitivity of 1.32 GHz/m^(−1),which is more than 4 times higher than those reported previously.

Enhancing hydrogen evolution and oxidation kinetics through oxygen insertion into nickel lattice

Nickel-based materials,including metallic Ni and Ni oxide,have been widely studied in the exploration of non-precious-metal hydrogen electrocatalysts,but neither pure Ni nor NiO is ideal for the hydrogen evolution reaction(HER)and hydrogen oxidation reaction(HOR).In this paper,an oxygen insertion strategy was applied on nickel to regulate its hydrogen electrocatalytic performance,and the oxygen-inserted nickel catalyst was successfully obtained with the assistance of tungsten dioxide support(denoted as O-Ni/WO_(2)).The partial insertion of oxygen in Ni maintains the face-centered cubic arrangement of Ni atoms,simultaneously expanding the lattice and increasing the lattice spacing.Consequently,the adsorption strength of^(*)H and^(*)OH on Ni is optimized,thus resulting in superior electrocatalytic performance of0-Ni/WO_(2)in alkaline HER/HOR.The Tafel slope of O-Ni/WO_(2)@NF for HER is 56 mV dec^(-1),and the kinetic current density of O-Ni/WO_(2)for HOR reaches 4.85 mA cm^(-2),which is ahead of most currently reported catalysts.Our proposed strategy of inserting an appropriate amount of anions into the metal lattice could provide more possibilities for the design of high-performance catalysts.

Free-moving-state microscopic imaging of cerebral oxygenation and hemodynamics with a photoacoustic fiberscope

We report the development of a head-mounted photoacoustic fiberscope for cerebral imaging in a freely behaving mouse.The 4.5-gram imaging probe has a 9-µm lateral resolution and 0.2-Hz frame rate over a 1.2-mm wide area.The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution,showing significantly different cerebrovascular responses to external stimuli under anesthesia and in the freely moving state.For example,when subjected to high-concentration CO_(2) respiration,enhanced oxygenation to compensate for hypercapnia can be visualized due to cerebral regulation in the freely moving state.Comparative studies exhibit significantly weakened compensation capabilities in obese rodents.This new imaging modality can be used for investigating both normal and pathological cerebrovascular functions and shows great promise for studying cerebral activity,disorders and their treatments.

Improvement in resolution of fiber-laser photoacoustic tomography based on a virtual-point concept

In this study,a virtual-point concept was introduced into fiber-laser photoacoustic tomography to improve the elevational image resolution.The flexible fiber laser was bent into an arc shape to conform to the ultrasound wavefront,which formed an ultrasound focus at the center of the arc.The synthetic aperture focusing technique was utilized to reconstruct the images;as a result,the elevational resolution particularly within the out-of-focus region was considerably improved compared to the resolution of an image retrieved by multiplexing the PA time-resolved signals with sound velocity.The all-optical fiber-laser photoacoustic tomography system with a high spatial resolution has potential for various applications,including biomedical research and preclinical/clinical diagnosis.

Broadband,Polarization-Sensitive,and Self-Powered High-Performance Photodetection of Hetero-Integrated MoS_(2)on Lithium Niobate

High-performance photodetectors hold promising potential in optical communication and imaging systems.However,conventional counterparts are suffering narrow detection range,high power consumption,and poor polarization sensitivity.Characteristics originating from switchable polarization in ferroelectrics can be used to optimize the photo-to-electric procedure and improve the photodetection performance.In this regard,we constructed a configuration by integrating 2-dimensional molybdenum disulfide(MoS_(2))with ferroelectric lithium niobate(LiNbO_(3)),resulting in the MoS_(2)/LiNbO_(3)heterostructured photodetector.Benefiting from the pyroelectric effect of LiNbO_(3),the limitation of bandgap on the detection range can be broken,thus broadening the response band of the detector to 365 to 1,064 nm,as well as enabling the self-powered characteristic.Meanwhile,high carrier mobility and decent light absorbance of MoS_(2)introduce robust light-matter interactions with the underlying LiNbO_(3),leading to ultrafast rise/fall times of≈150μs/250μs and switching ratios of up to≈190.Moreover,the highest responsivity,specific detectivity,and external quantum efficiency achieved were 17.3 A·W^(-1),4.3×10^(11)Jones,and 4,645.78%,respectively.Furthermore,because of the anisotropy of the spontaneous-polarized LiNbO_(3)substrate,the photocurrent of the device achieved a dichroic ratio of 7.42,comparing favorably to most MoS_(2)-based photodetectors.This work demonstrates the integration potential between ferroelectric LiNbO_(3)and 2-dimensional materials for high-performance photodetection.

High-sensitivity and fast-response fiber optic temperature sensor using an anti-resonant reflecting optical waveguide mechanism

Temperature sensing is essential for human health monitoring.High-sensitivity(>1 nm∕℃)fiber sensors always require long interference paths and temperature-sensitive materials,leading to a long sensor and thus slow response(6–14 s).To date,it is still challenging for a fiber optic temperature sensor to have an ultrafast(~ms)response simultaneously with high sensitivity.Here,a side-polished single-mode/hollow/single-mode fiber(SPSHSF)structure is proposed to meet the challenge by using the length-independent sensitivity of an anti-resonant reflecting optical waveguide mechanism.With a polydimethylsiloxane filled sub-nanoliter volume cavity in the SP-SHSF,the SP-SHSF exhibits a high temperature sensitivity of 4.223 nm/℃ with a compact length of 1.6 mm,allowing an ultrafast response(16 ms)and fast recovery time(176 ms).The figure of merit(FOM),defined as the absolute ratio of sensitivity to response time,is proposed to assess the comprehensive performance of the sensor.The FOM of the proposed sensor reaches up to 263.94(nm/℃)∕s,which is more than two to three orders of magnitude higher than those of other temperature fiber optic sensors reported previously.Additionally,a threemonth cycle test shows that the sensor is highly robust,with excellent reversibility and accuracy,allowing it to be incorporated with a wearable face mask for detecting temperature changes during human breathing.The high FOM and high stability of the proposed sensing fiber structure provide an excellent opportunity to develop both ultrafast and highly sensitive fiber optic sensors for wearable respiratory monitoring and contactless in vitro detection.

Fiber‑Optic Microfiber:Tracking Activity Enhancement and Suppression of Heterogeneous Photocatalysts

Obtaining detailed insight into the photocatalytic performance of heterogeneous photocatalytic materials,is important for evaluating material properties as well as guiding material design.However,capture of the detailed matter changes on a photocatalyst surface in real time,and in situ during photocatalysis remains challenging.This work reports a promising optical microfiber sensor integrating a photocatalytic reaction monolayer on an optical microfiber surface to monitor reaction kinetics using Cu_(2)O-based heterogeneous photocatalysts,as an example.The evanescent field of microfiber is used to track the photocatalytic process in real time,through the interaction with the catalytic layer,by monitoring the surface refractive index changes caused by adsorption and degradation.Since the catalytic layer is less than 1µm thick,the typical high-power light source can be replaced by low-power light irradiation.This method successfully reveals that relative to the pristine Cu_(2)O microspheres,the photocatalytic activity is enhanced by the incorporation of Ti_(3)C_(2)T_(x) MXene into Cu_(2)O,whereas incorporation of CdS into Cu_(2)O suppresses the activity.Compared with the existing methods used for photocatalysis evalu-ation,this optical microfiber can be directly employed in real matrices to track local photocatalytic performance.It can also provide details about the different adsorption/degradation kinetics of photocatalysts.It is suitable for most photocatalytic processes and is not limited to pollutants with characteristic UV–visible absorption spectra.This study provides important inspiration for the future development of in situ,real-time reaction assessment.

Near-perfect fidelity polarization-encoded multilayer optical data storage based on aligned gold nanorods

Encoding information in light polarization is of great importance in facilitating optical data storage(ODS)for information security and data storage capacity escalation.However,despite recent advances in nanophotonic techniques vastly en-hancing the feasibility of applying polarization channels,the data fidelity in reconstructed bits has been constrained by severe crosstalks occurring between varied polarization angles during data recording and reading process,which gravely hindered the utilization of this technique in practice.In this paper,we demonstrate an ultra-low crosstalk polarization-en-coding multilayer ODS technique for high-fidelity data recording and retrieving by utilizing a nanofibre-based nanocom-posite film involving highly aligned gold nanorods(GNRs).With parallelizing the gold nanorods in the recording medium,the information carrier configuration minimizes miswriting and misreading possibilities for information input and output,respectively,compared with its randomly self-assembled counterparts.The enhanced data accuracy has significantly im-proved the bit recall fidelity that is quantified by a correlation coefficient higher than 0.99.It is anticipated that the demon-strated technique can facilitate the development of multiplexing ODS for a greener future.

Band structure engineering in metal halide perovskite nanostructures for optoelectronic applications

Metal halide perovskite nanostructures have emerged as low-dimensional semiconductors of great significance in many fields such as photovoltaics,photonics,and optoelectronics.Extensive efforts on the controlled synthesis of perovskite nanostructures have been made towards potential device applications.The engineering of their band structures holds great promise in the rational tuning of the electronic and optical properties of perovskite nanostructures,which is one of the keys to achieving efficient and multifunctional optoelectronic devices.In this article,we summarize recent advances in band structure engineering of perovskite nanostructures.A survey of bandgap engineering of nanostructured perovskites is firstly presented from the aspects of dimensionality tailoring,compositional substitution,phase segregation and transition,as well as strain and pressure stimuli.The strategies of electronic doping are then reviewed,including defect-induced self-doping,inorganic or organic molecules-based chemical doping,and modification by metal ions or nanostructures.Based on the bandgap engineering and electronic doping,discussions on engineering energy band alignments in perovskite nanostructures are provided for building high-performance perovskite p-n junctions and heterostructures.At last,we provide our perspectives in engineering band structures of perovskite nanostructures towards future low-energy optoelectronics technologies.

Plasmon-enhanced nanosoldering of silver nanoparticles for high-conductive nanowires electrodes

The silver nanowires(Ag NWs)electrodes,which consist of incompact Ag nanoparticles(NPs)formed by multi-photon photoreduction,usually have poor conductivities.An effective strategy for enhancing conductivity of the Ag NWs elec-trodes is plasmon-enhanced nanosoldering(PLNS)by laser irradiation.Here,plasmon-enhanced photothermal effect is used to locally solder Ag NPs and then aggregates of these NPs grow into large irregular particles in PLNS process.Fi-nite element method(FEM)simulations indicate that the soldering process is triggered by localized surface plasmon-in-duced electric field enhancement at“hot-spots”.The effectiveness of PLNS for enhancing conductivity depends on laser power density and irradiation time.By optimizing the conditions of PLNS,the electrical conductivity of Ag NWs is signific-antly enhanced and the conductivityσs is increased to 2.45×107 S/m,which is about 39%of the bulk Ag.This PLNS of Ag NWs provides an efficient and cost-effective technique to rapidly produce large-area metal nanowire electrodes and capacitors with high conductivity,excellent uniformity,and good flexibility.

Blade-coated organic solar cells from non-halogenated solvent offer 17%efficiency

Organic solar cell(OSC)has attracted great interests due to its potential applications[1-9].To date,18%power conversion efficiency(PCE)has been achieved in single-junction OSC[10−13],indicating the feasibility of commercialization.This photovoltaic technology currently faces the performance gap between laboratory cells and large-area modules.

Classification of hyperspectral images for detection of hepatic carcinoma cells based on spectral-spatial features of nucleus

A distinguishing characteristic of normal and cancer cells is the difference in their nuclear chromatin content and distribution.This difference can be revealed by the transmission spectra of nuclei stained with a pH-sensitive stain.Here,we used hematoxylin-eosin(HE)to stain hepatic carcinoma tissues and obtained spectral-spatial data from their nuclei using hyper-spectral microscopy.The transmission spectra of the nuclei were then used to train a support vector machine(SVM)model for cell classification.Especially,we found that the chromatin distribution in cancer cells is more uniform,because of which the correlation coefficients for the spectra at different points in their nuclei are higher.Consequently,we exploited this feature to improve the SVM model.The sensitivity and specificity for the identification of cancer cells could be increased to 99%and 98%,respectively.We also designed an image-processing method for the extraction of information from cell nuclei to automate the identification process.

Moving-window bis-correlation coefficients method for visible and near-infrared spectral discriminant analysis with applications

The moving window bis corelation coefficients(MW BiCC)was proposed and employed for the discriminant analysis of transgenic sugarcane leaves and B-thalassemia with visible and near-infrared(Vis NIR)spectroscopy.The well-performed moving window principal component analysis linear discriminant analysis(MWPCA-LDA)was also conducted for comparison.A total of 306 transgenic(positive)and 150 nont ransgenic(negative)leave samples of sugarcane were collected and divided to calibration,prediction,and validation.The diffuse reflection spectra were corected using Savitzky-Golay(SG)smoothing with first-order derivative(d=1),third-degree polynomial(p=3)and 25 smpothing points(m=25).The selected waveband was 736-1054nm with MW-BiCC,and the positive and negative validation recognition rates(V_REC^(+),VREC^(-))were 100%,98.0%,which achieved the same effect as MWPCA-LDA.Another example,the 93 B-thalassemia(positive)and 148 nonthalassemia(negative)of human hemolytic samples were colloctod.The transmission spectra were corrected using SG smoothing withd=1,p=3 and m=53.Using M W-BiCC,many best wavebands were selected(e.g.,1116-1146,17941848 and 22842342nm).The V_REC^(+)and V_REC^(-)were both 100%,which achieved the same effect as MW-PCA-LDA.Importantly,the BICC only required ca lculating correlation cofficients between the spectrum of prediction sample and the average spectra of two types of calibration samples.Thus,BiCC was very simple in algorithm,and expected to obtain more applications.The results first confirmed the feasibility of distinguishing B-thalassemia and normal control samples by NIR spectroscopy,and provided a promising simple tool for large population thalassemia screening.

Operando optical fiber monitoring of nanoscale and fast temperature changes during photo-electrocatalytic reactions

In situ and continuous monitoring of thermal effects is essential for understanding photo-induced catalytic processes at catalyst's surfaces.However,existing techniques are largely unable to capture the rapidly changing temperatures occurring in sub-μm layers at liquid-solid interfaces exposed to light.To address this,a sensing system based on a gold-coated conventional single-mode optical fiber with a tilted fiber Bragg grating inscribed in the fiber core is proposed and demonstrated.The spectral transmission from these devices is made up of a dense comb of narrowband resonances that can differentiate between localized temperatures rapid changes at the catalyst's surface and those of the environment.By using the gold coating of the fiber as an electrode in an electrochemical reactor and exposing it to light,thermal effects in photo-induced catalysis at the interface can be decoded with a temperature resolution of 0.1℃and a temporal resolution of 0.1 sec,without perturbing the catalytic operation that is measured simultaneously.As a demonstration,stable and reproducible correlations between the light-to-heat conversion and catalytic activities over time were measured for two different catalysis processes(linear and nonlinear).These kinds of sensing applications are ideally suited to the fundamental qualities of optical fiber sensors,such as their compact size,flexible shape,and remote measurement capability,thereby opening the way for various thermal monitoring in hard-to-reach spaces and rapid catalytic reaction processes.

In situ plasmonic optical fiber detection of the state of charge of supercapacitors for renewable energy storage

In situ and continuous monitoring of electrochemical activity is key to understanding and evaluating the operation mechanism and efficiency of energy storage devices.However,this task remains challenging.For example,the present methods are not capable of providing the real-time information about the state of charge(SOC)of the energy storage devices while in operation.To address this,a novel approach based on an electrochemical surface plasmon resonance(SPR)optical fiber sensor is proposed here.This approach offers the capability of in situ comprehensive monitoring of the electrochemical activity(the electrode potential and the SOC)of supercapacitors(used as an example).The sensor adopted is a tilted fiber Bragg grating imprinted in a commercial single-mode fiber and coated with a nanoscale gold film for high-efficiency SPR excitation.Unlike conventional“bulk”detection methods for electrode activity,our approach targets the“localized”(sub-μm-scale)charge state of the ions adjacent to the electrode interface of supercapacitors by monitoring the properties of the SPR wave on the fiber sensor surface located adjacent to the electrode.A stable and reproducible correlation between the real-time charge–discharge cycles of the supercapacitors and the optical transmission of the optical fiber has been found.Moreover,the method proposed is inherently immune to temperature cross-talk because of the presence of environmentally insensitive reference features in the optical transmission spectrum of the devices.Finally,this particular application is ideally suited to the fundamental qualities of optical fiber sensors,such as their compact size,flexible shape,and remote operation capability,thereby opening the way for other opportunities for electrochemical monitoring in various hard-to-reach spaces and remote environments.

Photothermal nonlinear scattering of shell-isolated gold nanoparticles and applications in super-resolution imaging

In this Letter,we report on the investigations of nonlinear scattering of plasmonic nanoparticles by manipulating ambient environments.We create different local thermal hosts for gold nanospheres that are immersed in oil,encapsulated in silica glass and also coated with silica shells.In terms of regulable effective thermal conductivity,silica coatings are found to contribute significantly to scattering saturation.Benefitting from the enhanced thermal stability and the reduced plasmonic coupling provided by the shell-isolated nanoparticles,we achieve super-resolution imaging with a feature size of 52 nm(λ/10),and we can readily resolve pairs of nanoparticles with a gap-to-gap distance of 5 nm.

High performance and stable pure-blue quasi-2D perovskite light-emitting diodes by multifunctional zwitterionic passivation engineering

Despite the rapid advances of red and green perovskite light-emitting diodes(Pe LEDs),achieving high brightness with high external quantum efficiency(EQE)remains a challenge for the pure-blue Pe LEDs,which greatly hinders their practical applications,such as white-light illumination and in optical communication as a high-speed and low-loss light source.Herein,we report a high-performance pure-blue Pe LED based on mixed-halide quasi-2D perovskites incorporated with a zwitterionic molecule of 3-(benzyldimethylammonio)propanesulfonate(3-BAS).Experimental and density functional theory analysis reveals that 3-BAS can simultaneously eliminate non-radiative recombination loss,suppress halide migration,and regulate phase distribution for smoothing energy transfer in the mixed-halide quasi-2D perovskites,leading to the final perovskites with high photoluminescence quantum yield and robust spectrum stability.Thus,the highperformance pure-blue Pe LED with a recorded brightness with 1806 cd m-2and a relative higher EQE of 9.25%is achieved,which is successfully demonstrated in a visible light communication system for voice signal transmission.We pave the way for achieving highly efficient pure-blue Pe LEDs with great application potential in future optical communication networks.

Experimental demonstration of phase-sensitive multimode continuous variable quantum key distribution with improved secure key rate

We develop and experimentally demonstrate a phase-sensitive continuous variable quantum key distribution system with improved secure key rate.This is achieved using multimode coherent states with phase-conjugated subcarrier modulation and phase-sensitive detection.The local oscillator for phase-sensitive detection is regenerated from a polarization-multiplexed carrier wave via optical injection locking.The proposed scheme has a higher classical information capacity at a given number of received photons and exhibits a higher secure key rate when applying the security analysis of the GG02 protocol.Experimental results confirm the higher secret key rate and better excess noise tolerance of the new scheme compared to the typical implementation of GG02.

Dual-shot dynamics and ultimate frequency of all-optical magnetic recording on GdFeCo

Although photonics presents the fastest and most energy-efficient method of data transfer,magnetism still offers the cheapest and most natural way to store data.The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing.The discovery of all-optical magnetization reversal in GdFeCo with the help of 100fs laser pulses has further aroused intense interest in this compelling problem.Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching,the latter remains virtually unknown.Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27 Fe63.87 C09.T3.Varying the intensities of the shots and the shotto-shot separation,we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits.It is shown that although magnetic writing launched by the first shot is completed after 100 ps,a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps.Using two shots partially overlapping in space and minimally separated by 300 ps,we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit.

Efficiently Writing Bragg Grating in High-Birefringence Elliptical Microfiber for Label-Free Immunosensing with Temperature Compensation

Immunosensor is a powerful tool in healthcare and clinic,food and drug industry,and environmental protection.Label-free fiber-optic immunosensors have shown a myriad of advantages,such as high sensitivity,anti-electromagnetic interference,and afield measurement via the fiber network.However,the fiber-optic based sensor may bear the temperature cross-talk,especially under the warming condition for bio-activating the immune molecules.In this study,we proposed a highly birefringent microfiber Bragg grating for immunosensing with the temperature-compensation.The birefringent microfiber was drawn from the elliptical cladding multimode fiber that was ablated by the CO2 laser.The considerably large energy overlap region offered by the original multimode fiber favored the efficient inscription of FBG with high reflectivity.The dual reso-nances derived by the orthogonal polarization states presented similar temperature responsivities but significantly different ambient refractive index sensitivities,allowing the temperature-compensational RI sensing.The human immunoglobulin G(IgG)molecules were anchored on the surface of the microfiber grating probe by the covalent functionalization technique to enable the specific detection of the anti-IgG molecule.The proposed method promises a high-efficiency and low-cost design for the microfiber Bragg grating-based biosensor without being subjected to the temperature cross-sensitivity.