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A time-dependent change in the refractive index of a material leads to a change in the frequency of an optical beam passing through that medium. Here, we experimentally demonstrate that this effect-known as adiabatic frequency conversion (AFC)-can be significantly enhanced by a nonlinear epsilon-near-zero-based (ENZ-based) plasmonic metasurface. Specifically, by using a 63-nm-thick metasurface, we demonstrate a large, tunable, and broadband frequency shift of up to ∼11.2 THz with a pump intensity of 4 GW/cm2. Our results represent a decrease of ∼10 times in device thickness and 120 times in pump peak intensity compared with the cases of bare, thicker ENZ materials for the similar amount of frequency shift. Our findings might potentially provide insights for designing efficient time-varying metasurfaces for the manipulation of ultrafast pulses.

A light beam’s frequency can blueshift when the beam travels through a medium that exhibits a time-dependent decrease in the refractive index. Here we show that a metasurface made of a plasmonic an...

Orbital-angular-momentum (OAM) multiplexing has been utilized to increase the channel capacity in both millimeter-wave and optical domains. Terahertz (THz) wireless communication is attracting increasing attention due to its broadband spectral resources. Thus, it might be valuable to explore the system performance of THz OAM links to further increase the channel capacity. In this paper, we study through simulations the fundamental system-degrading effects when using multiple OAM beams in THz communications links under atmospheric turbulence. We simulate and analyze the effects of divergence, turbulence, limited-size aperture, and misalignment on the signal power and crosstalk of THz OAM links. We find through simulations that the system-degrading effects are different in two scenarios with atmosphere turbulence: (a) when we consider the same strength of phasefront distortion, faster divergence (i.e., lower frequency; smaller beam waist) leads to higher power leakage from the transmitted mode to neighbouring modes; and (b) however, when we consider the same atmospheric turbulence, the divergence effect tends to affect the power leakage much less, and the power leakage increases as the frequency, beam waist, or OAM order increases. Simulation results show that: (i) the crosstalk to the neighbouring mode remains

Chemodynamic therapy (CDT) with selective therapeutic and minimal side effects has attracted increasing attention in recent years. Nevertheless, the limited H2O2 and acid contents in the tumor microenvironment suppress the efficiency of the Fenton reaction. To overcome these issues, photothermal therapy (PTT) is employed to amplify the CDT effect and realize synergistic PTT/CDT. Herein, MoS2 sheets are functionalized with copper (Cu2O–MoS2), which integrates enhanced CDT and PTT to combat tumor cells. The 808 nm light activated Cu2O–MoS2 nanoplatform appears to be a potential candidate to improve the synergistic effect on the enhanced Fenton-like reaction and photothermal performance.

Surface acoustic wave (SAW) humidity sensors promise broad prospects for Internet of Things (IoT) applications due to the advantages of low cost, portability, and high sensitivity. However, previous researches mainly focused on developing SAW devices with higher resonant frequencies, or using new sensing materials to improve the performance of SAW humidity sensors. Few researches studied the specific response mechanism of SAW humidity sensors, which restricted further development of the sensors. In this paper, the sensing mechanism of a graphene oxide (GO) film-based SAW humidity sensor is thoroughly studied by investigating the mechanical and electrical parameters of the uniform GO membrane at different relative humidity (from 10% RH to 90% RH). After taking these parameters into consideration for the mechanism analysis, we quantitatively indicate that the mass loading (~800 ppm) and viscoelastic effects (~60 ppm) are the primary and secondary influence factors of the sensor’s humidity response respectively, while the acoustoelectric interaction has little effect on the sensitivity. [2020-0024]

Graphene oxide (GO), an important chemical precursor of graphene, can stably disperse in aqueous surrounding and undergo aggregation as metal cations introduced. The usual instability of GO with ions is caused by the shielding effect of ions and crosslinking between GO and ions. However, the dynamic stability of GO under ions exchange still remains unclear. Here, we investigated the dynamic dispersion stability of GO with metal ions and observed a redispersion behavior in concentrated Fe3+ solution, other than permanent aggregation. The exchange with Fe3+ ions drives the reversion of Zeta (ζ) potential and enables the redispersion to individual GO-Fe3+ complex sheets, following a dynamic electric double layer (EDL) mechanism. It is found that the specifically strong electrostatic shielding effect and coordination attraction between Fe3+ and functional oxygen groups allows the selective redispersion of GO in concentrated Fe3+ solution. The revealed dynamic dispersion stability complements our understanding on the dispersive stability of GO and can be utilized to fabricate graphene-metal hybrids for rich applications.

Highly porous graphene aerogels (GAs) demonstrate extensive applications in damping blocks, thermal insulation, sensors, catalyst carriers and energy storage because of their ultralow density, superelasticity and functional versatility. These properties have been regulated by topological structural design and composite of materials, but the effect of the structural unit on the properties of GA has not been reported. Herein, highly porous GAs with excellent mechanical performances and improved adsorption capacities have been prepared by a freezing-drying process. Ultra-flyweight (ρ

Piezoelectric cantilevers promise broad prospects for gas sensing and biosensing due to the high sensitivity and fast response. The strong correlation between the resonant frequency and sensitivity leads to numerous cantilever-based sensors using the high-order flexural mode to realize higher absolute sensitivity. However, experiment results show that the relative sensitivity of the sensors decreases with the increase of the mode order. Herein, we explain the relative sensitivity degeneration of normal cantilevers with a modified coefficient of equivalent mass, and propose a cantilever-based humidity sensor using high-frequency mode driven by interdigital electrodes (IDEs) to enhance the relative sensitivity. Compared with the high-order mode excited by normal configuration (70.4 MHz), the high-frequency mode driven by IDEs (77.3 MHz) demonstrates an improved sensitivity around 39.2 Hz $\cdot $ cm2/ng (1.68x) at 10%–90% relative humidity. The sensitivity enhancement by IDEs is consistent with the result calculated by the modified coefficient. [2020-0055]

Air stable, lightweight, and electrically conductive carbon-based films are highly desired for flexible electronic devices and products. Graphene film, a macroscopic assembly of individual graphene sheets, holds great potential to replace conventional brittle pyrolytic carbon film due to the excellent electrical transport property and flexibility. However, the electrical conductivity of graphene film is still inferior to metallic conductors, usually unstable in air as doped. We chose metal chloride (MoCl5) as air stable dopant and fabricated doped graphene film with well-controlled intercalation structure. The MoCl5 modified graphene film shows record high electrical conductivity of 1.73 × 107 S m−1, record high mobility of 2190.47 cm2 V−1 s−1, remarkable specific electrical conductivity exceeding benchmark metals (e.g., Au, Ag, Cu), and ultralow temperature coefficient of resistance (1.4 × 10−4 K−1). Importantly, the electrical conductivity and overall structure of MoCl5 intercalated films are exceptional stable in atmospheric environment, enabling wide applications in electronic devices, electromagnetic interference, and energy storage.

In this letter, we experimentally explore the limited-size aperture effects in an orbital-angular-momentum (OAM)-multiplexed free-space optical (FSO) data link for aerial platforms. 200-Gbit/s data transmission is demonstrated between a ground transmitter and a ground receiver via a flying, retro-reflecting unmanned-aerial-vehicle (UAV) over 100-m round-trip distance by multiplexing two OAM beams. Our results indicate that when the receiver aperture size is limited, both power loss and channel crosstalk would increase. With a receiver aperture diameter of >5 cm, bit error rate (BER) mostly below 3.8 × 10−3 has been achieved for both channels

TEMPO-mediated oxidation has been successfully used to prepare carboxylated chitin nanofibers (ChNFs) with purified chitins originating from the outer shells of crab and shrimp (α-form) or tubeworm (β-form). However, the method for obtaining carboxylated ChNFs with squid pen chitin (hydrated β-form) has not been developed yet. It might be due to the existence of the small amount of partial deacetylation (DD ≈ 9%) in the squid pen β-chitins. Herein, ultrafine (2–4 nm in width and several micrometers in length) and carboxylated β-ChNFs were fabricated directly from the squid pen with simultaneously removing of protein, CaCO3 and other non-chitin components by one-step oxidation procedure using ammonium persulfate (APS) and followed ultrasonic disintegration under acid conditions. When 45 wt% APS was used to react with squid pen, the carboxylate content of ChNFs reaches 0.802 mmol/g. Therefore, the β-ChNFs with anionically charged groups (COO−) can be dispersed stably in aqueous solution under basic conditions. Meanwhile, thus-obtained β-ChNFs aqueous solution even with very low concentration (0.8%) can be transformed to transparent, robust and moldable hydrogels by gas coagulation of acetic acid.

Extensive applications of carbon dioxide (CO2) in various fields, such as food industry, agricultural production, medical and pharmacological industries, have caused a great demand for high-performance CO2 sensors. However, most existing CO2 sensors suffer from poor performance in a wet environment and often cannot work accurately in a high humidity condition. In this study, a quartz crystal resonator (QCR) coated with a uniform layer of reduced graphene oxide (RGO) is proposed to detect both the concentrations of CO2 and water molecules simultaneously, which can be used to significantly minimize the humidity interference. Unlike the other common gas sensors, the RGO-based CO2 QCR sensor can be operated in different humidity levels and the concentration of CO2 can be quantified precisely and effectively. Moreover, it has a fast response (∼0.4 s), which is also suitable for respiration monitoring. Our results showed that before and after a volunteer did a low-intensity exercise, the sensor could detect the differences of concentrations of CO2 in the exhaled breath (i.e., 4.50 % and 5.15 %, respectively).

The orbital angular momentum (OAM) of photons presents a degree of freedom for enhancing the secure key rate of free-space quantum key distribution (QKD) through mode-division multiplexing (MDM). However, atmospheric turbulence can lead to substantial modal crosstalk, which is a long-standing challenge to MDM for free-space QKD. Here, we show that the digital generation of time-reversed wavefronts for multiple probe beams is an effective method for mitigating atmospheric turbulence. We experimentally characterize seven OAM modes after propagation through a 340-m outdoor free-space link and observe an average modal crosstalk as low as 13.2% by implementing real-time time reversal. The crosstalk can be further reduced to 3.4% when adopting a mode spacing $\Delta \ell$ of 2. We implement a classical MDM system as a proof-of-principle demonstration, and the bit error rate is reduced from $3.6\times 10^{-3}$ to be less than $1.3\times 10^{-7}$ through the use of time reversal. We also propose a practical and scalable scheme for high-speed, mode-multiplexed QKD through a turbulent link. The modal crosstalk can be further reduced by using faster equipment. Our method can be useful to various free-space applications that require crosstalk suppression., Comment: Supplemental Material is included

Novel forms of beam generation and propagation based on orbital angular momentum (OAM) have recently gained significant interest. In terms of changes in time, OAM can be manifest at a given distance in different forms, including: (1) a Gaussian-like beam dot that revolves around a central axis, and (2) a Laguerre-Gaussian (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$LG_{\ell ,p}$$\end{document}LGℓ,p) beam with a helical phasefront rotating around its own beam center. Here we explore the generation of dynamic spatiotemporal beams that combine these two forms of orbital-angular-momenta by coherently adding multiple frequency comb lines. Each line carries a superposition of multiple \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$LG_{\ell ,p}$$\end{document}LGℓ,p modes such that each line is composed of a different \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\ell$$\end{document}ℓ value and multiple p values. We simulate the generated beams and find that the following can be achieved: (a) mode purity up to 99%, and (b) control of the helical phasefront from 2π-6π and the revolving speed from 0.2–0.6 THz. This approach might be useful for generating spatiotemporal beams with even more sophisticated dynamic properties., Orbital angular momentum takes several forms in structured light beams. Here, the authors demonstrate control of dynamic spatiotemporal beams combining two forms of orbital angular momenta, by coherently adding frequency comb lines.

We utilize aperture diversity combined with multiple-mode receivers and multiple-input-multiple-output (MIMO) digital signal processing (DSP) to demonstrate enhanced tolerance to atmospheric turbulence and spatial misalignment in a 10 Gbit/s quadrature-phase-shift-keyed (QPSK) free-space optical (FSO) link. Turbulence and misalignment could cause power coupling from the fundamental Gaussian mode into higher-order modes. Therefore, we detect power from multiple modes and use MIMO DSP to enhance the recovery of the original data. In our approach, (a) each of multiple transmitter apertures transmits a single fundamental Gaussian beam carrying the same data stream, (b) each of multiple receiver apertures detects the signals that are coupled from the fundamental Gaussian beams to multiple orbital angular momentum (OAM) modes, and (c) MIMO DSP is used to recover the data over multiple modes and receivers. Our simulation shows that the outage probability could be reduced from > 0.1 to < 0.01 . Moreover, we experimentally demonstrate the scheme by transmitting two fundamental Gaussian beams carrying the same data stream and recovering the signals on OAM modes 0 and + 1 at each receiver aperture. We measure an up to ∼ 10 d B power-penalty reduction for a bit error rate (BER) at the 7% forward error correction limit for a 10 Gbit/s QPSK signal.

In this paper, we review high-capacity underwater optical communications using orbital angular momentum (OAM)-based spatial division multiplexing. We discuss methods to generate and detect blue–green optical data-carrying OAM beams as well as various underwater effects, including attenuation, scattering, current, and thermal gradients on OAM beams. Attention is also given to the system performance of high-capacity underwater optical communication links using OAM-based space division multiplexing. The paper closes with a discussion of a digital signal processing (DSP) algorithm to mitigate the inter-mode crosstalk caused by thermal gradients.

Nitrogen-enriched (N-enriched) carbon nanofiber aerogels (NCNAs) with an ultrafine nanofiber network structure were designed and prepared by using chitin nanofiber aerogels as the precursor. Because of the uniform nanofibrous architecture and nitrogen-rich composition of chitin nanofiber aerogels, the NCNAs exhibited large specific surface area (490–1597 m2 g–1) and a high nitrogen content (2.07–7.65%). As a consequence, supercapacitor electrodes prepared from NCNA-900 showed specific capacitances as high as 221 F g–1 at the current density of 1.0 A g–1 and good capacitance retention of 92% over 8000 cycles in a 6.0 mol L–1 KOH electrolyte without further activation. Moreover, the NCNA-900 could also be applied as an effective adsorbent for dye adsorption, such as Congo red (496 mg g–1) and Rhodanine B (489 mg g–1). In view of an excellent electrochemical performance and high adsorption capacities for dyes as well as cost-effective and eco-friendly approaches, NCNAs derived from marine chitin show great p...

We investigate the thickness-, distance- and loss-dependent interaction between nanoantenna arrays and an epsilon-near-zero (ENZ) thin film. We show the conditions for ultrastrong coupling and the length invariant pinning of antenna resonances on ENZ films.

We simulate a space-time light-sheet with reduced diffraction utilizing classical entanglement between multiple frequencies and Hermite-Gaussian (HG) modes. By increasing the number of modes, the ratio of Rayleigh ranges could be increased to > 10.

We simulate the generation of a space-time pulse with a controllable group velocity by classical entanglement of frequencies and multiple LG modes. Group velocities greater and smaller than the speed of light are achieved.

We simulate the generation of a near-diffraction- and dispersion-free OAM pulses with arbitrary group velocities. As the pulse OAM order increases, the group velocity almost remains the same while the temporal pulse width becomes longer.

We experimentally demonstrate adiabatic wavelength conversion using a time-varying epsilon-near-zero-based metasurface. We observe up to 47-mn redshift with 4-GW/cnr pump peak intensity. The wavelength shift depends on both pump-probe delay time and pmnp peak intensity.

We explore the use of a switchable single-photon detector (SPD) array scheme to reduce the effect of a detector’s deadtime for a multi-bit/photon quantum link. The case of data encoding using M possible orbital-angular-momentum (OAM) states is specifically studied in this paper. Our method uses N SPDs with a controllable M × N optical switch and we use a Monte Carlo-based method to simulate the quantum detection process. The simulation results show that with the use of the switchable SPD array, the detection system can allow a higher incident photon rate than what might otherwise be limited by detectors’ deadtime. For the case of M = 4 , N = 20 , a 50-ns deadtime for the individual SPDs, an average photon number per pulse of 0.1, and under the limit that at most 10 % of the photon-containing pulses are missed, the switchable SPD array will allow an incident photon rate of 2250 million counts/s (Mcts/s). This is 25 times the 90 Mcts/s incident photon rate that a non-switchable, 4-SPD array will allow. The increase in incident photon rate is more than the 5 times increase, which is the simple increase in the number of SPDs and the number of OAM encoding states (e.g., N ∕ M = 20 ∕ 4 ).

The resonance properties of a plasmonic dipole antenna array depend on its geometry and the properties of its surrounding medium. The linear optical properties of an array of plasmonic dipole antennas can be modified with the inclusion of an epsilon-near-zero (ENZ) thin film. In this work, we numerically investigate the roles of the antenna dimensions, the ENZ film thickness and loss, and the separation between the antenna and the ENZ film in determining the linear optical response of the antenna–ENZ metasurface. The results show that for a sufficiently small separation, the linear optical properties of the antenna array are determined by the strong or ultrastrong coupling with the ENZ film and are only weakly dependent on the antenna geometry. We show that for metasurfaces with thick, lossy ENZ films, the lower polariton branch is not observable due to the high loss of ENZ films. Since the dependence of the upper polariton on antenna length is weak, this results in a single antenna-length-invariant resonance. However, in the presence of low-loss ENZ films, the lower polariton branch is also visible for antenna–ENZ metasurfaces with thicker ENZ films, indicating a strong coupling between the antenna array and the ENZ film. For a given antenna geometry, the coupling strength increases with increasing thickness of the ENZ film and can reach up to ∼50% of the zero-permittivity frequency of the ENZ film, indicating an ultrastrong coupling between the plasmonic antenna array and the ENZ film.

Flexible and stretchable sensors are emerging and promising wearable devices for motion monitoring. Manufacturing a flexible and stretchable strain sensor with desirable electromechanical performance and excellent skin compatibility plays an essential role in building a smart wearable system. In this paper, a graphene-coated silk-spandex (GCSS) fabric strain sensor is prepared by reducing graphene oxide. The sensor functions as a result of conductive fiber extending and woven structure deforming. The conductive fabric can be stretched towards 60% with high sensitivity, and its performance remains constant after a 1000-cycle test. Based on its superior performance, the GCSS is successfully employed to detect full-range human movement and provide data for deep learning-based gesture recognition. This work offers a desirable method to fabricate low-cost strain sensors for industrial applications such as human movement detection and advanced information science.

In this paper, we experimentally explore using both mode and space (i.e., aperture) diversity to improve system reliability and performance of a free-space optical (FSO) link under atmospheric turbulence. When a system has a limited number of transmitter and receiver apertures, introducing mode diversity to the existing space diversity scheme might further enhance the system performance. We utilize orbital angular momentum (OAM) modes for mode diversity as an example. A 100-Gbit/s quadrature phase-shift keying FSO link is demonstrated through emulated turbulence using two transmitter and receiver aperture pairs. For each aperture pair, a Gaussian beam and an OAM beam are transmitted and received, and all four beams carry the same data stream. Our experimental results indicate that introducing mode diversity to space diversity systems could help to further reduce the variance of received signal power, thereby improving system tolerance to turbulence under a given detection threshold. Bit-error-rates (BERs) mostly below 3.8 × 10−3 are achieved under emulated turbulence with a Fried parameter of 0.4 mm. The dependence of system performance on different diversity schemes, OAM topological charge differential, and aperture spacing are also investigated.

We simulate and experimentally demonstrate the optical single-pixel identification of two-dimensional (2D) objects by analyzing the corresponding complex-valued (i.e, amplitude and phase) Laguerre–Gaussian​ ( LG l , p ) spectra containing both the azimuthal (i.e., l ) and radial (i.e., p ) indices. A sequence of optical beams, each carrying a different superposition of one LG mode and one fundamental Gaussian mode, propagate through the objects. The amplitude and phase contributions of each LG modal component are then obtained by four sequential power measurements using a single-pixel detector. We reconstruct the 2D spatial structures of fan-shaped objects with different orientation angles and an “SC” logo using the measured complex LG spectra that contain 31 different azimuthal and 31 different radial index values. The simulation and experimental results show that (i) the minima positions of the amplitude-only LG sub-spectra (fixed l = 0 , varying p ) are dependent on the object’s spatial information along its radial direction, (ii) the amplitude-only LG spectrum is likely to be insensitive to the object’s orientation angle, and (iii) the slopes of the phase-only LG sub-spectra (fixed p , varying l ) are linearly proportional to the object’s orientation angle.

Novel zwitterionic chitin nanofibers (ChNFs) decorated with both cationic (NH3+) and anionic (COO−) groups on the surface have broad applications in various environments. Herein, we demonstrate a rapid and high-yield (up to 85%) synthesis of a zwitterionic ChNF by the combination of partial deacetylation and oxidation using the TEMPO/NaClO2/NaClO system. Meanwhile, we present the potential application of a bio-based ChNF as an environmentally and doubly pH-responsive Pickering emulsifier to replace conventional pH-responsive Pickering emulsifiers such as inorganic nanoparticles or grafted polymers. This high yield preparation achieved by our method will be in favor of the large-scale applications of ChNFs.

Metal particle could be produced in the production and installation process of GIS, whose free movement is a significant security risk to GIS. At present, some related research focus on the movement behavior and partial discharge of individual particle, but for the movement behaviors and harmfulness of multiple particles are not very clear. In this paper, the 126 kV GIS prototype proportion shrinking test chamber was set up, the different number of metal particles with same size (10 mm length, 0.25 mm radius) were placed in the chamber, the movement behaviors of multiple particles were filmed by using a high speed camera, and discharge signals were recorded with the conventional pulse current detector and ultrasonic detector. The results of the study indicate that: At the operated voltage, the single particle (10 mm length, 0.25 mm radius) has a small jumping height but a high jumping frequency, and there is basically a collision case in each power frequency cycle. The number of linear particles affect the lifting voltage, and with the increase of the number of neighboring particles, the lifting voltage decrease, such as the lifting voltage of two aluminum particles with 10mm length and 0.25 mm radius could be reduced to 84% of the lifting voltage of a single particle, and the lifting voltage of eight aluminum particles could be reduced to 77%. Compared with single particle, the number of ultrasonic signals and partial discharge pulses of multiple particles becomes more obvious, and it could occur multiple collisions in a half power frequency cycle, but for a single particle, the maximum number of linear particle's collision in a half power frequency cycle is only one. With the increase of applied voltage, the flight time of the particles were significantly longer, and multiple discharge pulses were detected during a single collision, whose position showed “V” type distribution. At the operated voltage, the single linear particle had less harmfulness, while the existence of multiple linear particles, could greatly reduce the insulation strength of GIS, such as eight neighboring aluminum particles with 10 mm length and 0.25 mm radius could lead to a breakdown in the vicinity of the operated voltage, but the same size of the individual particle has not yet led to the breakdown of the test chamber at even twice of operated voltage. Under the different voltages, the maximum value of histogram of n-T/2 of linear particles remained unchanged, and through the histogram of n-T/2, it could estimate the number of particles in GIS.

Flexible electronics with continuous monitoring ability a extensively preferred in various medical applications. In this work, a flexible pressure sensor based on porous graphene (PG) is proposed for continuous cardiovascular status monitoring. The whole sensor is fabricated in situ by ink printing technology, which grants it the potential for large-scale manufacture. Moreover, to enhance its long-term usage ability, a polyethylene terephthalate/polyethylene vinylacetate (PET/EVA)-laminated film is employed to protect the sensor from unexpected shear forces on the skin surface. The sensor exhibits great sensitivity (53.99/MPa), high resolution (less than 0.3 kPa), wide detecting range (0.3 kPa to 1 MPa), desirable robustness, and excellent repeatability (1000 cycles). With the assistance of the proposed pressure sensor, vital cardiovascular conditions can be accurately monitored, including heart rate, respiration rate, pulse wave velocity, and blood pressure. Compared to other sensors based on self-supporting 2D materials, this sensor can endure more complex environments and has enormous application potential for the medical community.

We study the relationship between the input phase delays and the output mode orders when using a pixel-array structure fed by multiple single-mode waveguides for tunable orbital-angular-momentum (OAM) beam generation. As an emitter of a free-space OAM beam, the designed structure introduces a transformation function that shapes and coherently combines multiple (e.g., four) equal-amplitude inputs, with the k th input carrying a phase delay of ( k − 1 ) Δ φ . The simulation results show that (1) the generated OAM order ℓ is dependent on the relative phase delay Δ φ ; (2) the transformation function can be tailored by engineering the structure to support different tunable ranges (e.g., l = { − 1 } , { − 1 , + 1 } , { − 1 , 0 , + 1 } , or { − 2 , − 1 , + 1 , + 2 } ); and (3) multiple independent coaxial OAM beams can be generated by simultaneously feeding the structure with multiple independent beams, such that each beam has its own Δ φ value for the four inputs. Moreover, there is a trade-off between the tunable range and the mode purity, bandwidth, and crosstalk, such that the increase of the tunable range leads to (a) decreased mode purity (from 91% to 75% for l = − 1 ), (b) decreased 3 dB bandwidth of emission efficiency (from 285 nm for l = { − 1 } to 122 nm for l = { − 2 , − 1 , + 1 , + 2 } ), and (c) increased crosstalk within the C-band (from − 23.7 to − 13.2 d B when the tunable range increases from 2 to 4).

We experimentally demonstrate the utilization of adaptive optics (AO) to mitigate intra-group power coupling among linearly polarized (LP) modes in a graded-index few-mode fiber (GI FMF). Generally, in this fiber, the coupling between degenerate modes inside a modal group tends to be stronger than between modes belonging to different groups. In our approach, the coupling inside the L P 11 group can be represented by a combination of orbital-angular-momentum (OAM) modes, such that reducing power coupling in OAM set tends to indicate the capability to reduce the coupling inside the L P 11 group. We employ two output OAM modes l = + 1 and l = − 1 as resultant linear combinations of degenerate L P 11 a and L P 11 b modes inside the L P 11 group of a ∼ 0.6 - k m GI FMF. The power coupling is mitigated by shaping the amplitude and phase of the distorted OAM modes. Each OAM mode carries an independent 20-, 40-, or 100-Gbit/s quadrature-phase-shift-keying data stream. We measure the transmission matrix (TM) in the OAM basis within L P 11 group, which is a subset of the full LP TM of the FMF-based system. An inverse TM is subsequently implemented before the receiver by a spatial light modulator to mitigate the intra-modal-group power coupling. With AO mitigation, the experimental results for l = + 1 and l = − 1 modes show, respectively, that (i) intra-modal-group crosstalk is reduced by > 5.8 d B and > 5.6 d B and (ii) near-error-free bit-error-rate performance is achieved with a penalty of ∼ 0.6 d B and ∼ 3.8 d B , respectively.

The orbital angular momentum (OAM) of photons is a promising degree of freedom for high-dimensional quantum key distribution (QKD). However, effectively mitigating the adverse effects of atmospheric turbulence is a persistent challenge in OAM QKD systems operating over free-space communication channels. In contrast to previous works focusing on correcting static simulated turbulence, we investigate the performance of OAM QKD in real atmospheric turbulence with real-time adaptive optics (AO) correction. We show that even though our AO system provides a limited correction, it is possible to mitigate the errors induced by weak turbulence and establish a secure channel. The crosstalk induced by turbulence and the performance of AO systems is investigated in two configurations: a lab-scale link with controllable turbulence, and a 340 m long cross-campus link with dynamic atmospheric turbulence. Our experimental results suggest that an advanced AO system with fine beam tracking, reliable beam stabilization, precise wavefront sensing, and accurate wavefront correction is necessary to adequately correct turbulence-induced error. We also propose and demonstrate different solutions to improve the performance of OAM QKD with turbulence, which could enable the possibility of OAM encoding in strong turbulence.

In this Letter, we experimentally demonstrate beaconless beam displacement tracking for free-space optical communication link multiplexing multiple orbital angular momentum (OAM) beams, where the data-carrying OAM beams are used for position detection. 400 Gbit/s data transmission is demonstrated under emulated lateral displacement of up to ±10 mm with power penalties of less than 3 dB for all channels. Channel crosstalk is reduced by the beam tracking system to below −18 dB. Moreover, we investigate using a Gaussian beacon for beam displacement tracking, and achieve similar channel crosstalk and power penalties, compared with using the beaconless beam tracking.

Based on a NaOH/urea aqueous system, a facile and convenient method was proposed to prepare graphene oxide/cellulose composite films with superior mechanical performances and excellent ultraviolet-shielding properties. Unexpectedly, it is found that more uniform dispersion of graphene oxide (GO) in a cellulose/NaOH/urea aqueous solution could be realized by mixing them at low temperature rather than room temperature. Epichlorohydrin (ECH) was introduced as a cross-linking agent to enhance the performance of GO/cellulose composite films. With the synergistic effect of chemical cross-linking and the strong hydrogen bonding interaction between GO and the cellulose matrix, the tensile strength, elongation at break and fracture energy of the thus prepared composite film with 0.5 wt% GO loading were significantly improved by 78%, 172% and 397%, respectively, compared with the pure cellulose film. Moreover, it is found that the cross-linked GO/cellulose composite film also possessed excellent ultraviolet-shielding properties. These enhanced properties indicate that the cellulose based composite material has great potential for use as a high performance bioplastic film.

We demonstrate that a designed bimetallic chip is capable of improving the performance of a surface plasmon resonance (SPR) sensor based on angular interrogation. Through a numerical simulation and a refractometry experiment, we prove that this bimetallic chip can effectively reduce the noise level by about a factor of 2 compared to the traditional SPR sensors that only use a single gold film. The bimetallic chip presents a lower refractive index resolution of 5.3 × 10−7 refractive index units. In addition, the enhancement of the electric field intensity at the surface of the configuration by a factor of 2 makes it possible to have a high sensitivity in a larger region, which promotes the biosensing applications of the chip. Through a simple and novel method for the detection of cadmium ions (Cd2+) based on the bimetallic configuration, a detection level for Cd2+ (0.01 μM or 1.12 ppb) can be realized, which compares favorably with similar studies.

Nanoparticles have been widely used in biomedical research as drug carriers or imaging agents for living animals. Blood circulation is crucial for the delivery of nanoparticles, which enter the bloodstream through injection, inhalation, or dermal exposure. However, the clearance kinetics of nanoparticles in blood circulation has been poorly studied, mainly because of the limitations of conventional detection methods, such as insufficient blood sample volumes or low spatial-temporal resolution. In addition, formation of nanoparticle aggregates is a key determinant for biocompatibility and drug delivery efficiency. Aggregation behavior of nanoparticles in blood is studied using dynamic light scattering in serum or serum protein solutions, which is still very different from in vivo condition. In this work, we monitored the dynamics of nanoparticle concentration and formation of nanoparticle aggregates in the bloodstream in live animals using in vivo flow cytometry (IVFC). The results indicated that nanoparticles in smaller size could stay longer in the bloodstream. Polyethylene glycol (PEG)-modification could prolong circulating time and reduce the formation of aggregates in the blood circulation. Our work shows that IVFC can be a powerful tool for pharmacokinetic studies of nanoparticles and other drug carriers, assessing cell-targeting efficiency, as well as potentially measuring cardiac output and hepatic function in vivo.

We experimentally demonstrate and investigate the effect of limited aperture size on a 200-Gbit/s retro-reflected free-space optical link between a ground station and a UAV up to ∼100-m roundtrip distance by multiplexing 2 OAM beams.

We experimentally investigate the performance of a quantum communication link using Laguerre-Gaussian (LG) modes with different radial indices. Quantum symbol error rate (QSER)

We experimentally investigate the effect of multiple scattering on the performance of an 80-Gbit/s orbital angular momentum (OAM) multiplexed optical wireless link regarding both power loss and channel crosstalk.

We experimentally demonstrate adaptive-optics compensation of emulated atmospheric turbulence for an OAM-based quantum communication link with a classical Gaussian beam used as probe. The turbulence-induced quantum-symbol-error-rate is reduced by « 76 % with the compensation.

Novel hybrid nanomaterials composed of graphene and chitin nanofibers (ChNFs) were successfully prepared by one-pot ball milling. Under strong shear and collision force of ball milling, graphite was exfoliated to mono-layer or few-layer graphene with the assistance of chitin nanofibers. Unexpectedly, the hybridization of exfoliated graphene and ChNFs was realized simultaneously. Morphology analysis observed that the ChNFs were adsorbed tightly on the surface of graphene, providing for reduced graphene hydrophobicity and enhanced stability of the hybrid dispersion. In addition, the concentration of exfoliated graphene reaches up to 1.5 mg ml−1. Strong interaction between graphene and ChNFs may benefit from the large amounts of carboxylate groups on the surface of ChNFs, which was prepared by TEMPO-mediated oxidation of chitin. As prepared graphene/ChNFs hybrids can remarkably enhance both the tensile strength and toughness of Poly(vinyl alcohol). This study provides a green, simple and large-scale synthesis method for preparing water-dispersible graphene/ChNFs hybrid nanobuilding blocks, which shows great promise potential in various applications requiring biocompatibility, hydrophilicity, electrical conductivity and strong mechanical properties.

Light beams can be characterized by their complex spatial profiles in both intensity and phase. Analogous to time signals, which can be decomposed into multiple orthogonal frequency functions, a light beam can also be decomposed into a set of spatial modes that are taken from an orthogonal basis. Such decomposition can potentially provide a tool for spatial spectrum analysis, which may enable stable, accurate, and robust extraction of physical object information that may not be readily achievable using traditional approaches. As a proof-of-concept example, we measure an object’s opening angle using orbital-angular-momentum (OAM) -based complex spectrum, achieving a >15 dB signal-to-noise ratio. Moreover, the dip (i.e., notch) positions of the OAM intensity spectrum are dependent on an object’s opening angle but independent of the opening’s angular orientation, whereas the slope of the OAM phase spectrum is dependent on the opening’s orientation but independent of the opening angle.

We experimentally demonstrate simultaneous turbulence mitigation and channel demultiplexing in a 200 Gbit/s orbital-angular-momentum (OAM) multiplexed link by adaptive wavefront shaping and diffusing (WSD) the light beams. Different realizations of two emulated turbulence strengths (the Fried parameter r 0 = 0.4 , 1.0 m m ) are mitigated. The experimental results show the following. (1) Crosstalk between OAM l = + 1 and l = − 1 modes can be reduced by > 10.0 and > 5.8 d B , respectively, under the weaker turbulence ( r 0 = 1.0 m m ); crosstalk is further improved by > 17.7 and > 19.4 d B , respectively, under most realizations in the stronger turbulence ( r 0 = 0.4 m m ). (2) The optical signal-to-noise ratio penalties for the bit error rate performance are measured to be ∼ 0.7 and ∼ 1.6 d B under weaker turbulence, while measured to be ∼ 3.2 and ∼ 1.8 d B under stronger turbulence for OAM l = + 1 and l = − 1 mode, respectively.

We experimentally demonstrate beam displacement tracking and correction using orbital-angular-momentum (OAM) beams based position detection over a 400-Gbit/s OAM-multiplexed link. Power penalties

We experimentally demonstrate an OAM-based quantum communication link populated by a classical channel. OAM enables an up to 100-Mbit/s quantum data rate as well as an additional 18.5-dB separation between the quantum and classical channels.

We experimentally demonstrate spatial multiplexing of an orbital angular momentum (OAM)-encoded quantum channel and a classical Gaussian beam with a different wavelength and orthogonal polarization. Data rates as large as 100 MHz are achieved by encoding on two different OAM states by employing a combination of independently modulated laser diodes and helical phase holograms. The influence of OAM mode spacing, encoding bandwidth, and interference from the co-propagating Gaussian beam on registered photon count rates and quantum bit error rates is investigated. Our results show that the deleterious effects of intermodal crosstalk effects on system performance become less important for OAM mode spacing Δ≥2 (corresponding to a crosstalk value of less than -18.5 dB). The use of OAM domain can additionally offer at least 10.4 dB isolation besides that provided by wavelength and polarization, leading to a further suppression of interference from the classical channel.

To obtain detailed information about electrochemistry reactions, a two-electrode electrochemical surface plasmon resonance (EC-SPR) sensor has been proposed. We describe the theory of potential modulation for this novel sensor and determine the factors that can change the SPR resonance angle. The reference electrode in three-electrode configuration was eliminated, and comparing with several other electrode materials, activated carbon (AC) is employed as the suitable counter electrode for its potential stability. Just like three-electrode configuration, the simpler AC two-electrode system can also obtain detailed information about the electrochemical reactions.