Limin Tong

• Zhejiang University

Polarization-entangled photon pairs are essential sources for photonic quantum information processing. However, generating entangled photon pairs with large detuning via spontaneous parametric down-conversion (SPDC) often requires complex configurations to compensate for phase matching. Here, we propose a simple and efficient scheme to generate pol...

Enhancement and active control of light-matter interactions at the atomic scale is important for developing next-generation nanophotonic and quantum optical devices. Here, we demonstrate electric control of excitonic strong coupling and electroluminescence (EL) by integrating a semiconductor monolayer into a nanometer gap of single electrically dri...

Materials usually fracture before reaching their ideal strength limits. Meanwhile, materials with high strength generally have poor ductility, and vice versa. For example, gold with the conventional face-centered cubic (FCC) phase is highly ductile while the yield strength (~102 MPa) is significantly lower than its ideal theoretical limit. Here, th...

Small organic molecules are essential building blocks of our universe, from cosmic dust to planetary surfaces to life. Compared to their well-known gaseous and liquid forms that have been extensively studied, small organic molecules in the form of ice at low temperatures receive much less attention. Here, we show that supercooled small-molecule dro...

Measurement of masses of microscale objects or weak force with ultrahigh sensitivity (down to nanogram/piconewton level) and compact configuration is highly desired for fundamental research and applications in various disciplines. Here, by using freestanding gold flakes with high reflectivity (≈98% at 980 nm) as the sample tray and silica microfibe...

Polarization-entangled photon pairs are essential sources for photonic quantum information processing. However, generating entangled photon pairs with large detuning via spontaneous parametric down-conversion (SPDC) often requires complex configurations to compensate for phase matching. Here, we propose a simple and efficient scheme to generate pol...

Tactile sensors with capability of multiaxial force perception play a vital role in robotics and human–machine interfaces. Flexible optical waveguide sensors have been an emerging paradigm in tactile sensing due to their high sensitivity, fast response, and antielectromagnetic interference. Herein, a flexible multiaxial force sensor enabled by U‐sh...

Enhancement and active control of light-matter interactions at the atomic scale is important for developing next-generation nanophotonic and quantum optical devices. Here, we demonstrate electric control of both excitonic strong coupling and electroluminescence by integrating semiconductor monolayers into a nanometer gap of electrically driven nano...

Ultrathin plasmonic nanostructures offer an unparalleled opportunity for the study of light–matter interactions at the nanoscale and realization of compact nanophotonic devices. In this study, we introduce an ultrathin gold nanoribbon array and demonstrate an electric approach to actively tuning its plasmonic resonance, which leveraging the extreme...

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 centimete...

Two-dimensional single crystal metals, in which the behavior of highly confined optical modes is intertwined with quantum phenomena, are highly sought after for next-generation technologies. Here, we report large area (>10⁴ μm²), single crystal two-dimensional gold flakes (2DGFs) with thicknesses down to a single nanometer level, employing an atomi...

The development of neuromorphic visual systems has recently gained momentum due to their potential in areas such as autonomous vehicles and robotics. However, current machine visual systems based on silicon technology usually contain photosensor arrays, format conversion, memory and processing modules. As a result, the redundant data shuttling betw...

We demonstrate a novel fiber-compatible variable optical attenuator (VOA) based on a tunable microfiber coupler, which is assembled by embedding two parallel 2.5- $\mu \text{m}$ -diameter microfibers in a 250- $\mu \text{m}$ -thickness polydimethylsiloxane (PDMS) film with a separation of $2.5~\mu \text{m}$ and a coupling length of 3 mm. Based...

Dispersion management is vital for nonlinear optics and ultrafast lasers. We demonstrate that group velocity dispersion (GVD, or second-order dispersion, i.e., β2) 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 experiment...

Optical micro/nanofiber (MNF) is a quasi-one-dimensional free-standing optical waveguide with a diameter close to or less than the vacuum wavelength of the light. Combining the tiny geometry with high refractive-index contrast between the core and the surrounding, the MNF exhibits favorable optical properties such as tight optical confinement, stro...

Narrow bandgap materials have garnered significant attention within the field of broadband photodetection. However, the performance is impeded by diminished absorption near the bandgap, resulting in a rapid decline in photoresponsivity within the mid‐wave infrared (MWIR) and long‐wave infrared (LWIR) regions. Furthermore, they mostly worked in cryo...

Single-nanoparticle detection has received tremendous interest due to its significance in fundamental physics and biological applications. Here, we demonstrate an optical nanofibre-enabled microfluidic sensor for the detection and sizing of nanoparticles. Benefitting from the strong evanescent field outside the nanofibre, a nanoparticle close to th...

Fiber-tip sensors based on the Fabry-Perot interferometer (FPI) are one of the most widely used devices for temperature and pressure measurements in space-confined scenarios. However, the deposited metal films with a polycrystalline structure tend to form microcracks under strain, which can undermine the optical quality factor and thus sensing perf...

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 spectr...

An efficient fiber‐to‐chip interface via an intermediated CdS nanowire is demonstrated. The fiber mode is firstly squeezed through a fiber taper drawn at the end of a single‐mode fiber, then evanescently coupled into an intermediated CdS nanowire with a longitudinally tapering profile, and finally coupled into an on‐chip silicon waveguide (SiW) via...

As miniature fibre-optic platforms, micro/nanofibres (MNFs) taper-drawn from silica fibres have been widely studied for applications from optical sensing, nonlinear optics to optomechanics and atom optics. While continuous-wave (CW) optical waveguiding is frequently adopted, so far almost all MNFs are operated in low-power region (e.g., <0.1 W). He...

Owing to its unique structure, morphology, and crystal quality, low-dimensional (L-D) ice has attracted increasing attention in recent years. With a size (at least in one dimension) between that of a single water molecule and a snowflake, L-D ice does not only appear as an intermediate state during the dimensional change but can also manifest extra...

Humanoid tactility has been boosting robotic intelligence in object recognition, dexterous manipulation, and human–robot interaction. For many artificial tactile sensors, especially those based on optical principles, inflexibility, bulkiness, and monomodality limit their potential to function as humanoid skins. Herein, by embedding lab‐made optical...

Interface interactions in 2D vertically stacked heterostructures play an important role in optoelectronic applications, and photodetectors based on graphene/InSe heterostructures show promising performance nowadays. However, nonlinear optical property studies based on the graphene/InSe heterostructure are insufficient. Here, we fabricated a graphen...

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 electromagneti...

Laser based on single plasmonic nanoparticle can provide optical frequency radiation far beyond the diffraction limit and is one of the ultimate goals of nanolasers, yet it remains a challenge to be realized because of the inherently high Ohmic loss. Here, we report the direct observation of lasing in microfiber-coupled single plasmonic nanoparticl...

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...

The ability to sense heat and touch is essential for healthcare, robotics, and human–machine interfaces. By taking advantage of the engineerable waveguiding properties, we design and fabricate a flexible optical microfiber sensor for simultaneous temperature and pressure measurement based on theoretical calculation. The sensor exhibits a high tempe...

Wearable human–machine interface (HMI) is an advanced technology that has a wide range of applications from robotics to augmented/virtual reality (AR/VR). In this study, an optically driven wearable human-interactive smart textile is proposed by integrating a polydimethylsiloxane (PDMS) patch embedded with optical micro/nanofibers (MNF) array with...

We report a new technique for the realization of second-order correlation ($g^2(\tau)$) measurement under low-repetition-rate pulsed excitation (1 kHz), with timing jitter calibrated to restore lateral $g^2(\tau)$ curves and determine $g^2(0)$. We use CdSe nanowire (NW) laser to demonstrate the jitter-calibrated $g^2(\tau)$ measurement, where $g^2(...

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...

One-dimensional crystalline nanowire structures have been widely used as nano-waveguides in nanophotonics. The propagation constant of a certain waveguiding mode in the nanowire is essential to its optical waveguiding properties. To estimate the propagation constant, commonly the cross section of such a nanowire is treated as a circle with a diamet...

In recent years, significant efforts have been made to develop ultrafast laser source around 2- $\mu \text{m}$ wavelength. Meanwhile, the characterization of the ultrashort pulses within ultracompact footprints has been attracting growing interests. Here relying on the transverse second-harmonic generation in a single CdTe microwire, we successful...

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 and molecular detection. However, the optical quality factor and thus performance of these nanoconstructs are undermined by the gr...

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...

Microsphere‐assisted optical imaging has been proved straightforward and cost‐effective for super‐resolution imaging in material science and biomedical research. Optically transparent microspheres with a high refractive index are critical for achieving superior super‐resolution capabilities yet remain to be further exploited. Here, the use of As2S3...

Plasmon decay via the surface or interface is a critical process for practical energy conversion and plasmonic catalysis. However, the relationship between plasmon damping and the coupling between the plasmon and 2D materials is still unclear. The spectral splitting due to plasmon–exciton interaction impedes the conventional single‐particle method...

With diameters close to the wavelength of the guided light, optical microfibers (MFs) can guide light with tight optical confinement, strong evanescent fields and manageable waveguide dispersion and have been widely investigated in the past decades for a variety of applications. Compared to silica MFs, which are ideal for working in visible and nea...

Fiber-optic anemometers have attracted an increasing attention over the past decade owing to their high sensitivity, wide dynamic range, low power consumption, and immunity to electromagnetic interference. However, expensive instruments may limit their practical applications. Herein, a new type of airflow sensor based on optical micro/nanofiber (MN...

By placing a single Au nanoparticle on the surface of a cadmium sulfide (CdS) nanowire, we demonstrate strong coupling of localized surface plasmon resonance (LSPR) modes in the nanoparticle and whispering gallery modes (WGMs) in the nanowire. For a 50-nm-diameter Au-nanosphere particle, strong coupling occurs when the nanowire diameter is between...

Plasmon decay via the surface or interface is a critical process for practical energy conversion and plasmonic catalysis. However, the relationship between plasmon damping and the coupling between the plasmon and 2D materials is still unclear. The spectral splitting due to plasmon-exciton interaction impedes the conventional single-particle method...

Ice goes bendy One well known characteristic of ice is that it fractures instead of bending when strained. This characteristic is caused by the inevitable defects introduced into the ice structure during solidification. Xu et al. show that very thin, carefully grown ice microfibers can bend a lot, up to about 11%, and still remain elastic (see the...

Photoactuators have attracted tremendous interest yet most of them rely on free-space illumination, which requires a line-of-site low-loss optical path. While waveguide photoactuators can overcome this limitation, their actuating performances are fundamentally restricted by the nature of standard optical fibres. Herein, we demonstrated miniature ph...

Single-mode fiber coupler with variable coupling ratio is a flexible tool for optical fiber applications. Here we demonstrate a microfiber based coupler with compact size and wide tuning range. The coupler consists of two identical single-mode microfibers that are fabricated via parallel pulling process. By adjusting the twisting angle between thes...

Bending losses of sharply bent optical nanofibers or nanowires coupling with Au nanoparticles (Au NPs) are investigated using a finite-difference time-domain (FDTD) method. Relying on the ultra-tight optical confinement of the Au NPs, bending losses of the sharply bent optical nanofibers or nanowires can be effectively reduced by attaching Au NPs t...

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 C...

Realizing general processing applicable to various materials by one basic tool has long been considered a distant dream. Fortunately, ultrafast laser–matter interaction has emerged as a highly universal platform with unprecedented optical phenomena and provided implementation paths for advanced manufacturing with novel functionalities. Here, we rep...

Optical micro/nanofibers (MNFs) can be applied for ultrasensitive tactile sensing with fast response and compact size, which are attractive for restoring tactile information in minimally invasive robotic surgery and tissue palpation. Herein, we present a compact tactile sensor (CTS) with a diameter of 1.5 mm enabled by an optical MNF. The CTS provi...

A compact variable fiber coupler consisting of two identical microfibers is demonstrated. By twisting microfibers, the coupling ratio varies from 3.15% to 98.5% due to the change of evanescent field interaction length.

A single-nanoparticle plasmon laser with ultratight optical confinement in all three dimensions is a long-cherished but yet to be realized goal. Here we propose an experimentally realizable plasmon laser using a single nanorod. We show that, by harnessing a Au-nanorod cavity with a large gain from a Purcell-enhanced stimulated emission rate and gre...

The ability to generate a laser field with ultratight spatial confinement is important for pushing the limit of optical science and technology. Although plasmon lasers can offer sub-diffraction-confined laser fields, it is restricted by a trade-off between optical confinement and loss of free-electron oscillation in metals. We show here an all-diel...

By integrating a free-standing cadmium sulfide (CdS) nanowire onto a silicon nitride (SiN) photonic chip, we demonstrate a highly compact on-chip single-mode CdS nanowire laser. The mode selection is realized using a Mach-Zehnder interferometer (MZI) structure. When the pumping intensity exceeds the lasing threshold of 4.9 kW/cm2, on-chip single-mo...

On the basis of transverse second harmonic generation(TSHG) in a CdS nanowire-assembled Sagnac loop, we demonstrate an optical correlator for ultrashort pulse characterization with an overall footprint as small as ∼46 × 120 μm2. Pulses to be measured are coupled into the input port of a Sagnac-loop-based correlator and subsequently split into two c...

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 ${\rm{A}}{{\rm{s}}_2}{{\rm{S}}_3}$ glass fibers, and the mid-IR microfiber Bragg gratings (mFBGs) are inscribed on microfibers using interference patterns of nea...

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...

The rapid development of nanotechnology has spurred great efforts in improving thermo-optic (TO) modulators with higher performances for optical signal processing and interconnects, in which reducing the heating structure and increasing the heating efficiency is one of the most effective approaches to faster response and lower-power consumption. He...

Surface plasmons are usually excited by diffraction-limited optical methods with the use of bulky optical components, which greatly limits the miniaturization and chip-scale high-density integration of plasmonic devices. By integrating a plasmonic nanostructure with a tunnel junction, plasmonic modes in the nanostructure can be directly excited by...

Multifunctional skin-like sensors play an important role in next-generation healthcare, robotics, and bioelectronics. Here, we report a skin-like wearable optical sensor (SLWOS) enabled by a stretchable, flexible, and attachable patch embedded with an optical micro/nanofibre (MNF), which is highly compatible with human skin, curved surface, or clot...

Subwavelength diameter micro/nanofiber (MNF) provides excellent platform for many applications. In this work, we fabricate subwavelength diameter MNFs with ultra-long waist and analyze the propagation loss origin for such fibers. Transmittance as high as 99.4% is measured for MNF with a waist length of 10 cm and diameter of $1.2\mu \text{m}$ , an...

Wearable optical sensors are attracting intensive research interests owing to their advantage of high sensitivity, fast response, and immunity to electromagnetic interferences. However, tunable optical properties and reconfigurable sensor structures remain great challenges for the wearable optical sensors. Herein, flexible liquid‐filled fiber adapt...

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 demo...

Electronic skin, a class of wearable electronic sensors that mimic the functionalities of human skin, has made remarkable success in applications including health monitoring, human-machine interaction and electronic-biological interfaces. While electronic skin continues to achieve higher sensitivity and faster response, its ultimate performance is...

Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range. However, the reported fast graphene photodetectors mainly operate in the 1.55 μm wavelength band. In this work, we propose and realize high-performance waveguide photodetectors based on bolometric/photoconductiv...

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...

A lithium niobate on 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 demonst...

A novel type of mid-IR microresonator, the chalcogenide glass (ChG) microfiber knot resonator (MKR), is demonstrated, showing easy fabrication, fiber-compatible features, resonance tunability, and high robustness. ChG microfibers with typical diameters around 3 μm are taper-drawn from As2S3 glass fibers and assembled into MKRs in liquid without sur...

Precise diameter control is critical for many optical micro/nanofiber (MNF) applications. We demonstrate real-time MNF diameter control with improved accuracy and precision. Different from earlier works, a white light source is applied to monitor the transmittance during fiber pulling process. Terminated directly by the transmission intensity drops...

Flexible strain sensors play an important role in electronic skins, wearable medical devices, and advanced robots. Herein, a highly sensitive and fast response optical strain sensor with two evanescently coupled optical micro/nanofibers (MNFs) embedded in a polydimethylsiloxane (PDMS) film is proposed. The strain sensor exhibits a gauge factor as h...

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...

Phase matching is crucial for effective nonlinear frequency conversion. Recent advances in photonic miniaturization greatly promote implementations of efficient nonlinear frequency conversion in integrated photonic devices. Here, we investigate second-harmonic generation in coupled nonlinear waveguides. We develop a nonlinear optical coupled-mode t...

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-c...

Miniaturizing spectrometers Spectroscopy is a ubiquitous characterization tool spanning most scientific and many industrial disciplines. Most handheld spectrometers are based on tabletop optical components, which limits the scale to which these spectrometers can be shrunk. To address the desire for miniaturized spectrometers with a micrometer-scale...

Plasmonic nanolasers using sub‐diffraction‐limit plasmonic cavity modes can pursue extreme lasing conditions with ultrahigh optical confinement. Recent progresses on plasmonic nanolasers from both theoretical and experimental aspects are introduced in article number 1900334 by Xin Guo, Limin Tong and co‐workers; future prospects, challenges and las...

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-...