High-sensitivity fiber-tip acoustic sensor with ultrathin gold diaphragm.

Miniature acoustic sensors with high sensitivity are highly desired for applications in medical photoacoustic imaging, acoustic communications and industrial nondestructive testing. However, conventional acoustic sensors based on piezoelectric, piezoresistive and capacitive detectors usually require a large element size on a millimeter to centimeter scale to achieve a high sensitivity, greatly limiting their spatial resolution and the application in space-confined sensing scenarios. Herein, by using single-crystal two-dimensional gold flakes (2DGFs) as the sensing diaphragm of an extrinsic Fabry-Perot interferometer on a fiber tip, we demonstrate a miniature optical acoustic sensor with high sensitivity. Benefiting from the ultrathin thickness (∼8 nm) and high reflectivity of the 2DGF, the fiber-tip acoustic sensor gives an acoustic pressure sensitivity of ∼300 mV/Pa in the frequency range from 100 Hz to 20 kHz. The noise-equivalent pressure of the fiber-tip acoustic sensor at the frequency of 13 kHz is as low as 62.8 µPa/Hz1/2, which is one or two orders of magnitude lower than that of reported optical acoustic sensors with the same size.

Stretch tuning of dispersion in optical microfibers.

Dispersion management is vital for nonlinear optics and ultrafast lasers. We demonstrate that group velocity dispersion (GVD, or second-order dispersion, i.e., ß2) and group delay dispersion (GDD) in optical microfibers can be tuned simply by stretch due to their remarkable features of small diameter and diameter-dependent dispersion. We experimentally demonstrate that a pulling force of just a few mN would elongate the optical microfibers by up to 5%, bringing a significant change in the ß2 and GDD. This change can be increment or decrement, lying on the diameter of optical microfibers. Therefore, 10-cm-long optical microfibers would provide a GDD change of 104 fs2 when elongated by 5%, well in the elastic limit. Remarkably, this change is equivalent to the GDD (not GDD change) provided by a 0.5-m-long single-mode fiber. Experimental results and simulations show that the GDD change is due to the interplay between elongation, diameter shrink, and refractive index decrease. Benefited from the easy manipulation, tiny pulling force required, and full integration with conventional optical fibers, stretch tuning of dispersion in optical microfibers would find applications in dispersion management for ultrafast lasers and nonlinear optics.

Molecular Plasmonics with Metamaterials.

Molecular plasmonics, the area which deals with the interactions between surface plasmons and molecules, has received enormous interest in fundamental research and found numerous technological applications. Plasmonic metamaterials, which offer rich opportunities to control the light intensity, field polarization, and local density of electromagnetic states on subwavelength scales, provide a versatile platform to enhance and tune light-molecule interactions. A variety of applications, including spontaneous emission enhancement, optical modulation, optical sensing, and photoactuated nanochemistry, have been reported by exploiting molecular interactions with plasmonic metamaterials. In this paper, we provide a comprehensive overview of the developments of molecular plasmonics with metamaterials. After a brief introduction to the optical properties of plasmonic metamaterials and relevant fabrication approaches, we discuss light-molecule interactions in plasmonic metamaterials in both weak and strong coupling regimes. We then highlight the exploitation of molecules in metamaterials for applications ranging from emission control and optical modulation to optical sensing. The role of hot carriers generated in metamaterials for nanochemistry is also discussed. Perspectives on the future development of molecular plasmonics with metamaterials conclude the review. The use of molecules in combination with designer metamaterials provides a rich playground both to actively control metamaterials using molecular interactions and, in turn, to use metamaterials to control molecular processes.

Clinical Analysis of Atorvastatin Calcium, Fenofibrate, and Acipimox in the Treatment of Hypertriglyceridemia-induced Acute Pancreatitis.

Background: Hypertriglyceridemia-induced acute pancreatitis (HTG-AP) is an increasingly recognized and potentially severe form of acute pancreatitis. The effective management of HTG-AP is critical due to its association with significant morbidity and mortality. HTG-AP poses a considerable burden on affected individuals and healthcare systems. It can result in persistent upper abdominal pain, nausea, vomiting, abdominal distension, fever, and in severe cases, hypotension or shock and multiple organ dysfunction. Standard treatment strategies often involve lipid-lowering agents, but the optimal therapeutic approach remains a subject of ongoing research. This study aims to evaluate the efficacy of atorvastatin calcium, fenofibrate, and acipimox, either individually or in combination, in the treatment of HTG-AP, providing insights into more effective management strategies. Methods: 150 HTG-AP patients admitted to the first hospital of Putian from June 2020 to December 2022 were selected. The age range of the patients included in the study was between 30 and 70 years, with an average age of approximately 48 years. The cohort consisted of 90 males and 60 females, resulting in a male-to-female ratio of 3:2. The patients were grouped: atorvastatin calcium, acipimox, fenofibrate, fenofibrate + Atorvastatin calcium, fenofibrate + acipimox, and no drug. The therapeutic effects and clinical indicators of the six groups were compared. Results: Patients in the fenofibrate + acipimox and fenofibrate groups experienced significantly reduced hospitalization duration compared to the other groups. They also had shorter abdominal pain relief time and gastrointestinal function relief time. Additionally, these groups had lower peak levels of amylase (an enzyme) and cholesterol compared to the other groups. In terms of neutrophil (NEUT) increase, the fenofibrate + acipimox, atorvastatin calcium, and fenofibrate groups had significantly lower peak levels compared to the other groups, indicating a less pronounced increase in NEUT. Furthermore, the fenofibrate and acipimox groups exhibited significantly lower peak levels of C-reactive protein (CRP) compared to the other groups. CRP is an indicator of inflammation. On the other hand, the atorvastatin calcium group had higher levels of procalcitonin (a marker of infection) and a higher peak score on the acute physiology and chronic health evaluation II (APACHE II) scale, which assesses the severity of acute pancreatitis, compared to the other groups (all P < .05). Conclusion: The findings of this study highlight the effectiveness of combining fenofibrate and acipimox in the treatment of HTG-AP, leading to rapid disease recovery and significant improvement in clinical symptoms. These results have important implications for clinical practice, as the combination therapy can be widely adopted as an effective treatment strategy for HTG-AP patients. Moreover, this study provides valuable insights into the management of HTG-AP and suggests that lipid-lowering agents, such as atorvastatin calcium and fenofibrate, play a crucial role in the treatment of this condition. However, further research is needed to explore the optimal dosages, treatment durations, and potential side effects of these medications in HTG-AP patients.

Waveguide-Integrated Light-Emitting Metal-Insulator-Graphene Tunnel Junctions.

Ultrafast interfacing of electrical and optical signals at the nanoscale is highly desired for on-chip applications including optical interconnects and data processing devices. Here, we report electrically driven nanoscale optical sources based on metal-insulator-graphene tunnel junctions (MIG-TJs), featuring waveguided output with broadband spectral characteristics. Electrically driven inelastic tunneling in a MIG-TJ, realized by integrating a silver nanowire with graphene, provides broadband excitation of plasmonic modes in the junction with propagation lengths of several micrometers (∼10 times larger than that for metal-insulator-metal junctions), which therefore propagate toward the junction edge with low loss and couple to the nanowire waveguide with an efficiency of ∼70% (∼1000 times higher than that for metal-insulator-metal junctions). Alternatively, lateral coupling of the MIG-TJ to a semiconductor nanowire provides a platform for efficient outcoupling of electrically driven plasmonic signals to low-loss photonic waveguides, showing potential for applications at various integration levels.

Atomically Smooth Single-Crystalline Platform for Low-Loss Plasmonic Nanocavities.

Nanoparticle-on-mirror plasmonic nanocavities, capable of extreme optical confinement and enhancement, have triggered state-of-the-art progress in nanophotonics and development of applications in enhanced spectroscopies. However, the optical quality factor and thus performance of these nanoconstructs are undermined by the granular polycrystalline metal films (especially when they are optically thin) used as a mirror. Here, we report an atomically smooth single-crystalline platform for low-loss nanocavities using chemically synthesized gold microflakes as a mirror. Nanocavities constructed using gold nanorods on such microflakes exhibit a rich structure of plasmonic modes, which are highly sensitive to the thickness of optically thin (down to ∼15 nm) microflakes. The microflakes endow nanocavities with significantly improved quality factor (∼2 times) and scattering intensity (∼3 times) compared with their counterparts based on deposited films. The developed low-loss nanocavities further allow for the integration with a mature platform of fiber optics, opening opportunities for realizing nanocavity-based miniaturized photonic devices for practical applications.

Polarization-independent photon up-conversion with a single lithium niobate waveguide.

We propose a polarization-independent up-conversion protocol for single-photon detection at telecom band with a single thin-film periodically poled lithium niobate waveguide. By choosing the proper waveguide parameters, the waveguide dispersion can compensate the crystal birefringence so that quasi-phase-matching conditions for transverse electric and transverse magnetic modes can be simultaneously fulfilled with single poling period. With this scheme, randomly-polarized single photons at 1550 nm can be up-converted with a normalized conversion efficiency of 163.8%/W cm2.

Twin-nanofiber structure for a highly efficient single-photon collection.

Optical nanofiber-based single-photon source has attracted considerable interest due to its property of seamless integration with a single-mode fiber. With nanostructure engraved in the nanofiber, the single-photon collection efficiency can be greatly boosted with enhanced interaction between the single quantum emitter and the guided light. However, the prerequisite nanofabrication processes introduce complexities and extra loss. Here, we demonstrate that by simply placing a quantum emitter in the gap of two parallel nanofibers, single-photon coupling efficiency may reach 54.2%. Our numerical simulation results indicate that photon coupling efficiency of such simple structure is insensitive to the discrepancy in nanofiber radii, which further reduces the difficulties in device fabrication.

Photonic Nanolaser with Extreme Optical Field Confinement.

We proposed a photonic approach to a lasing mode supported by low-loss oscillation of polarized bound electrons in an active nano-slit-waveguide cavity, which circumvents the confinement-loss trade-off of nanoplasmonics, and offers an optical confinement down to sub-1-nm level with a peak-to-background ratio of ∼30 dB. Experimentally, the extremely confined lasing field is realized as the dominant peak of a TE_{0}-like lasing mode around 720-nm wavelength, in 1-nm-level width slit-waveguide cavities in coupled CdSe nanowire pairs. The measured lasing characteristics agree well with the theoretical calculations. Our results may pave a way towards new regions for nanolasers and light-matter interaction.

Batch Fabrication of High-Quality Infrared Chalcogenide Microsphere Resonators.

Optical microsphere resonators working in the near- and mid-infrared regions are highly required for a variety of applications, such as optical sensors, filters, modulators, and microlasers. Here, a simple and low-cost approach is reported for batch fabrication of high-quality chalcogenide glass (ChG) microsphere resonators by melting high-purity ChG powders in an oil environment. Q factors as high as 1.2 × 106 (7.4 × 105 ) are observed in As2 S3 (As2 Se3 ) microspheres (≈30 µm in diameter) around 1550-nm wavelength. Smaller microspheres with sizes around 10 µm also show excellent resonant responses (Q ≈ 2.5 × 105 ). Based on the mode splitting of an azimuthal mode in a microsphere resonator, eccentricities as low as ≈0.13% (≈0.17%) for As2 S3 (As2 Se3 ) microspheres are measured. Moreover, by coupling ChG microspheres with a biconical As2 S3 fiber taper, Q factors of ≈1.7 × 104 (≈1.6 × 104 ) are obtained in As2 S3 (As2 Se3 ) microspheres in the mid-infrared region (around 4.5 µm). The high-quality ChG microspheres demonstrated here are highly attractive for near- and mid-infrared optics, including optical sensing, optical nonlinearity, cavity quantum electrodynamics, microlasers, nanofocusing, and microscopic imaging.

Bio-inspired flow rate sensor based on optical microfiber embedded soft film.

Inspired by superficial neuromasts in the lateral line of fish for the sensing of flow rate, we report a bionic optical microfiber flow rate sensor by embedding a U-shaped microfiber into a thin PDMS film. When immersed into liquid, the PDMS film is deflected by the flowing liquid, resulting in a bending-dependent transmittance change of the embedded microfiber which is directly related to the flow rate of the liquid. The flow rate sensor exhibits a low detection limit (< 0.05 L/min), a high resolution (0.005 L/min), and a fast response time (12 ms). In addition, the sensitivity and working range of the sensor are tunable in a wide range via adjusting the thickness of PDMS film, the microfiber diameter, and/or the working wavelength.

Efficient light coupling between an ultra-low loss lithium niobate waveguide and an adiabatically tapered single mode optical fiber.

A lithium niobate on an insulator ridge waveguide allows constructing high-density photonic integrated circuits thanks to its small bending radius offered by the high index contrast. Meanwhile, the significant mode-field mismatch between an optical fiber and the single-mode lithium niobate waveguide leads to low coupling efficiencies. Here, we demonstrate, both numerically and experimentally, that the problem can be solved with a tapered single mode fiber of an optimized mode field profile. Numerical simulation shows that the minimum coupling losses for the TE and TM mode are 0.32 dB and 0.86 dB, respectively. Experimentally, though without anti-reflection coating, the measured coupling losses for TE and TM mode are 1.32 dB and 1.88 dB, respectively. Our technique paves a way for a broad range of on-chip lithium niobate applications.

Optimizing up-conversion single-photon detectors for quantum key distribution.

High-performance single-photon detectors (SPDs) at 1550-nm band are critical for fiber-based quantum communications. Among many types of SPDs, the up-conversion SPDs based on periodically poled lithium niobate waveguides are of great interest. Combined with a strong pump laser, the telecom single-photons are converted into short wavelength ones and detected by silicon-based SPDs. However, due to the difficulty of precise controlling waveguide profile, the direct coupling between a single-mode fiber and the waveguide is not efficient. Here by utilizing fiber taper with proper diameter, optimal mode-matching is achieved and coupling efficiency up to 93% is measured. With an optimized design, a system detection efficiency of 36% and noise counting rate of 90 cps are realized. The maximum detection efficiency is characterized as 40% with a noise counting rate of 200 cps. Numerical simulation results indicate that our device can significantly improve the performance of QKD and extend the communication distance longer than 200 km.

Mid-infrared microfiber Bragg gratings.

We report mid-infrared (mid-IR) Bragg gratings fabricated on sub-wavelength-diameter chalcogenide glass (ChG) microfibers. ChG microfibers with diameters around 3 µm are tapered drawn from As2S3 glass fibers, and the mid-IR microfiber Bragg gratings (mFBGs) are inscribed on microfibers using interference patterns of near bandgap light at a 532 nm wavelength. At a wavelength of about 4.5 µm, the mFBG has an extinction ratio of 15 dB and a positive photo-induced refractive index change of 2×10-2. The dependence of the grating formation on accumulated influence of exposure power density and time is investigated. The mid-IR mFBGs demonstrated here may be used as building blocks for micro-photonic circuits or devices in the mid-IR spectral range.

Full-field real-time characterization of creeping solitons dynamics in a mode-locked fiber laser.

Creeping solitons, which belong to the class of pulsating solitons, can be meaningful for fundamental physics owing to their fruitful nonlinear dynamics. Their characteristics in mode-locked lasers have been studied theoretically, but it is difficult to experimentally observe evolution dynamics in real time. Here, we have experimentally observed the temporal and spectral evolution dynamics of creeping solitons in a passively mode-locked fiber laser by employing time-lens and dispersive Fourier transform technique. With the aid of Raman amplification, the measured recording length of the time lens in the asynchronous mode could be substantially improved. Temporal soliton snaking motion and spectral breathing dynamics are experimentally obtained, confirming intrinsic feature of pulsation dynamics. These results display how single-shot measurements can offer new insights into ultrafast transient dynamics in nonlinear optics.

Simultaneous generation of ultrabroadband noise-like pulses and intracavity third harmonic at 2 µm.

We demonstrated that ultrabroadband noise-like pulses (NLPs) spanning from below 1600 nm to beyond 2300 nm can be generated in Tm-doped fiber lasers enabled by an optical microfiber. Meanwhile, pronounced red light around 660 nm was also observed, which was attributed to the intracavity third harmonic generation (THG) of ultrashort pulses by harnessing the intermodal phase matching in the optical microfiber. As far as we know, it is the first time to simultaneously observe the ultrabroadband NLPs and the intracavity THG in ultrafast fiber lasers, and it is anticipated that these ultrabroadband NLPs can be adopted as a compact broadband source for optical spectroscopy around 2 µm and a wonderful potential seed for supercontinuum generation in the mid-infrared. Moreover, the THG of the intracavity high peak power NLPs in ultrafast fiber lasers provides a new kind of fiber-format visible light source.

Measuring the refractive index of optical adhesives at cryogenic temperatures.

The development of photonic quantum information technologies requires research on the properties of optical adhesives at cryogenic temperatures. In the process of developing microfiber (MF)-coupled superconducting nanowire single-photon detectors (SNSPDs), we invented a cryogenic-temperature refractive index (RI) measurement method based on a kind of MF device. The device was put into the cryostat to observe the variance of MF transmittance with temperature. Then an RI-temperature relationship was established through the correspondence between the confinement conditions of MFs of various diameters in an optical adhesive-${{\rm MgF}_2}$MgF2 environment and transmittance-temperature curves. Using this method, we analyzed the thermal-optical properties of a commercial fluorinated acrylic optical adhesive and obtained the RI values of the adhesive at various temperatures. The results were successfully applied in the development of broadband and high-efficiency MF-coupled SNSPDs.

Direct observation of multimode interference in rare-earth doped micro/nanofibers.

Modal inspection of optical fibers is important for multimode application but it is challenging to collect in-situ information of propagating modes for evaluation and manipulation. Here we demonstrate direct observation of multimode interference in Er3+/Yb3+ co-doped micro/nanofibers. Luminescent interference patterns are visualized by visible up-conversion of Er3+ ions and are used for establishing the existence of higher order modes co-propagating with fundamental modes. We use fast Fourier transform to analyze the patterns in detail and obtain excellent agreement between experiment and calculation on beat lengths of the interference. Effective index differences among higher order modes and a fundamental mode of a microfiber are also experimentally investigated with the assistance of interference patterns, revealing the characteristic of modal dispersions.

Self-phase modulation in single CdTe nanowires.

We measure the transmission of near-infrared ps pulses through single CdTe nanowires. Benefitting from the strong light confinement and large effective nonlinearity of these nanowires, a significant spectral broadening of ∼ 5 nm and nonlinear phase shift of a few π due to self-phase modulation (SPM) is observed experimentally at coupled peak power of a dozen W with a propagating length down to several hundred µms. A nonlinear-index coefficient (n2) as high as (9.5 ± 1.4) × 10-17 m2/W at 1550 nm is extracted from transmission spectra, corresponding to a nonlinear parameter (γ) of ∼ 1050 W-1m-1. The simulations indicate a spectral broadening more than 1.5 µm in single nanowire when pumped by fs pulses in anomalous dispersion regime. The obtained results suggest that, CdTe nanowire is promising in developing ultracompact nonlinear optical devices for microphotonic circuits.

Ultra-broadband microfiber-coupled superconducting single-photon detector.

Broadband photon detectors are a key enabling technology for various applications such as spectrometers, light detection and ranging. In this work, we report on an ultra-broadband single-photon detector based on a microfiber (MF)-coupled superconducting nanowires structure operating in the spectral range from visible to near-infrared light. The MF-coupled superconducting nanowire single-photon detector (SNSPD) is formed by placing an MF on top of superconducting niobium nitride (NbN) nanowires, allowing ultra-broadband photon detection due to their nearly lossless transmission/absorption and nearly unity internal efficiency for ultra-broad waveband. The simulation results indicate that with optimal device structure, the optical absorption with efficiency > 90% can be realized over a wavelength range of 350 nm to 2150 nm. The fabricated MF-coupled SNSPD shows unparalleled broadband system detection efficiencies (SDEs) of more than 50% from 630 nm to 1500 nm. The SDEs reach 66% at 785 nm and 45% at 1550 nm. These results pave the way for ultra-broadband weak light detection with quantum-limit sensitivity.