Modular coupling MOF nanozyme with natural enzyme on hollow fiber membrane for rapid and reusable detection of H2O2 and glucose.

A novel strategy based on gradient porous hollow fiber membrane (GPF) is proposed for the modular assembly of enzyme-nanozyme cascade systems. The porous structure of GPF provided sufficient specific surface area, while the gradient structure effectively minimized the leaching of enzymes and nanozymes. To enhance stability, we prepared and immobilized metal-organic framework (MOF) nanozymes, resulting in the fabrication of GPF-MOF with excellent stability and reusability for colorimetric H2O2 detection. To improve specificity and expand the detection range, micro-crosslinked natural enzymes were modularly assembled, using glucose oxidase as the model enzyme. The assembled system, GPF-mGOx@MOF, achieved a low detection limit of 0.009 mM and a linear range of 0.2 to 11 mM. The sensor retained 87.2% and 80.7% of initial activity after being stored for 49 days and 9 recycles, respectively. Additionally, the reliability of the biosensor was validated through glucose determination of human blood and urine samples, yielding comparable results to a commercial glucose meter.

Distributed twist sensing using frequency-scanning φ-OTDR in a spun fiber.

In this paper, a novel distributed twist sensor based on frequency-scanning phase-sensitive optical time-domain reflectometry (φ-OTDR) in a spun fiber is proposed and demonstrated. Owing to the unique helical structure of the stress rods in the spun fiber, fiber twist gives rise to the variation of the effective refractive index of the transmitting light, which can be quantitatively retrieved through frequency shift using frequency-scanning φ-OTDR. The feasibility of distributed twist sensing has been verified by both simulation and experiment. For proof of concept, distributed twist sensing over a 136 m spun fiber with a 1 m spatial resolution is demonstrated, and the measured frequency shift shows a quadratic fitting dependence on the twist angle. In addition, the responses of both clockwise and counterclockwise twist directions have also been explored and the experiment result indicates that the twist direction can be discriminated since the frequency shift directions are opposite in the correlation spectrum. The proposed twist sensor possesses some outstanding advantages, including high sensitivity, distributed twist measurement and twist direction recognition capability, etc., which is very promising for specific applications in industry, e.g., structural health monitoring, bionic robots, etc.

High-resolution liquid level sensor utilizing a microwave photonics interrogated multicore fiber interferometer.

We propose and experimentally demonstrate a high-resolution, high-sensitivity liquid level sensor based on a multicore fiber (MCF) Michelson interferometer (MI), where the sensing fiber is securely affixed to a cantilever beam, such that liquid level variations will change the beam's curvature, meanwhile leading to a substantial phase difference between the two interfering arms of the MI, and the sensor is interrogated using a microwave photonics filter (MPF) system, which can provide greatly enhanced measurement resolution compared to the traditional optical wavelength demodulation methods. The angular position of the MCF is precisely calibrated to ensure optimal sensitivity of the MI sensor. As a result, within a measurement range of up to ±14 cm, the proposed liquid level sensor achieves a sensitivity of 10.35 MHz/cm and an impressive resolution of 0.04835 cm. The proposed sensor has unique advantages of high sensitivity, superior resolution, long-term stability, etc.

Single-Atom Nanozymes: Fabrication, Characterization, Surface Modification and Applications of ROS Scavenging and Antibacterial.

Nanozymes are nanomaterials with intrinsic natural enzyme-like catalytic properties. They have received extensive attention and have the potential to be an alternative to natural enzymes. Increasing the atom utilization rate of active centers in nanozymes has gradually become a concern of scientists. As the limit of designing nanozymes at the atomic level, single-atom nanozymes (SAzymes) have become the research frontier of the biomedical field recently because of their high atom utilization, well-defined active centers, and good natural enzyme mimicry. In this review, we first introduce the preparation of SAzymes through pyrolysis and defect engineering with regulated activity, then the characterization and surface modification methods of SAzymes are introduced. The possible influences of surface modification on the activity of SAzymes are discussed. Furthermore, we summarize the applications of SAzymes in the biomedical fields, especially in those of reactive oxygen species (ROS) scavenging and antibacterial. Finally, the challenges and opportunities of SAzymes are summarized and prospected.

Broad-Spectrum Reactive Oxygen Species Scavenging and Activated Macrophage-Targeting Microparticles Ameliorate Inflammatory Bowel Disease.

Inflammatory bowel disease (IBD) is a refractory chronic inflammatory disease. An excessively high level of reactive oxygen species (ROS) in the colon is one of the characteristics and pathogenic factors of IBD. Therefore, scavenging excessive ROS is a feasible method to treat IBD. Because ROS include many types of species, scavenging a single kind of ROS is not enough to reduce the ROS level and cure IBD effectively. Herein, broad-spectrum ROS scavenging and activated macrophage-targeting microparticles (MPs) are successfully fabricated by coprecipitation of catalase (CAT) and bovine serum albumin into a MnCO3 template followed by deposition of polydopamine (PDA), assembly of targeting molecules on the surface, and finally removal of MnCO3. The CAT content of MPs is about 34.1%. The obtained MPs can effectively scavenge the broad spectrum of ROS and retain 88% of the radical scavenging activity even after the treatment of simulated gastric fluid. The surface-modified dextran sulfate endows MPs with the targeting ability toward activated macrophages, achieving a better therapeutic effect. The MPs with components mostly derived from natural substances exhibit good biocompatibility and can show excellent ROS scavenging ability in cell experiments. In animal experiments, oral administration of a proper dosage of MPs can substantially mitigate colonic inflammation, as evidenced by disease activity index scores reduced by ∼40%, reduced body weight loss, and the production of typical proinflammatory cytokines in the inflammatory colon. This kind of MP can also be utilized for the treatment of other inflammatory diseases.

Encapsulation of Methylene Blue in Zeolitic Imidazolate Framework-90 Nanoparticles to Protect Its Photodynamic Activity.

Methylene blue (MB) is widely used as a photosensitizer in photodynamic therapy applications. However, it is easily reduced by reductases in biological environments, which hampers its further applications. Here, we developed a one-pot method to synthesize MB-encapsulated and poly(vinylpyrrolidone) (PVP)-modified zeolitic imidazolate framework-90 (ZIF-90) nanoparticles (MB@ZIF-90/PVP NPs). The NPs show intact crystalline structure with improved colloidal dispersity and stability both in water and in the medium for cell culture. The size of the enzymes is much larger than the pore size of ZIF-9; thus, the access of reductive enzymes to encapsulated MB is prohibited, resulting in the protection of MB's photodynamic activity. Furthermore, cell experiments confirm that MB@ZIF-90/PVP NPs have lower dark cytotoxity than equivalent free MB but can efficiently induce photodynamic damage to tumor cells even in the presence of reductive enzymes upon light irradiation.

Femtosecond laser enabled selective micro-holes drilling on the multicore-fiber facet for displacement sensor application.

We experimentally demonstrate a femtosecond laser enabled selective micro-holes drilling technique on the multicore-fiber facet. The precise position of individual cores at the seven-core fiber facet is initially locked by the image processing algorithm, and then six micro-holes are successfully fabricated after the pulse energy of femtosecond laser is optimized. Meanwhile, the use of fabricated seven-core fiber for the application of reflective intensity-modulated fiber optics displacement sensor (RIM-FODS) is comprehensively investigated. By using the beam propagation method (BPM), we theoretically investigate the effect of micro-hole depth on the RIM-FODS performance, in terms of both dead zone and measurement range. We identify that, with the increase of micro-hole depth, the dead zone range can be substantially reduced at the expense of measurement range reduction. However, multiple micro-holes with a successive depth difference can overcome such problem. When the micro-holes with depths of 5, 10, 15, 20, 25, 30 µm are fabricated on the seven-core fiber facet, and the dead zone range can be substantially reduced from 150 µm to 20 µm, together with an extension of measurement range from 250 µm to 400 µm.

Kernel mapping for mitigating nonlinear impairments in optical short-reach communications.

Nonlinear impairments induced by the opto-electronic components are one of the fundamental performance-limiting factors in high-speed optical short-reach communications, significantly hindering capacity improvement. This paper proposes to employ a kernel mapping function to map the signals in a Hilbert space to its inner product in a reproducing kernel Hilbert space, which has been successfully demonstrated to mitigate nonlinear impairments in optical short-reach communication systems. The operation principle is derived. An intensity modulation/direct detection system with 1.5-µm vertical cavity surface emitting laser and 10-km 7-core fiber achieving 540.68-Gbps (net-rate 505.31-Gbps) has been carried out. The experimental results reveal that the kernel mapping based schemes are able to realize comparable transmission performance as the Volterra filtering scheme even with a high order.

Long-period fiber gratings inscribed in few-mode fibers for discriminative determination.

We successfully fabricated the long-period fiber gratings in few-mode fibers (FMF-LPFGs) with micro-tapered method, which are different from the traditional LPFGs that only couple the fundamental mode to different cladding modes to obtain multiple resonant dips. There are two resonant dips on the transmission spectrum of the FMF-LPFGs, which are induced by the coupling between the fundamental mode and the low-order cladding mode LP03 (dip 1) and the coupling between the fundamental mode and the high-order core mode LP11 (dip 2). Due to the difference of the coupling mechanism involved in two dips, the shift of resonant wavelengths has different characteristics with the variation of the external environment parameter. The corresponding wavelength of dip 1 exhibits a red shift as the temperature increased. But for dip 2, the resonant wavelength has a blue shift. In addition, the two dips have different temperature and strain sensitivities. Therefore, discriminative determination of temperature and strain is realized by establishing the cross coefficient matrix, and the relative measurement error is less than 3%. What's more, we theoretically analyzed the reason why the two resonant wavelengths shift toward opposite direction with the increase of temperature and toward the same direction with the increase of strain.

Realization of linear-mapping between polarization Poincaré sphere and orbital Poincaré sphere based on stress birefringence in the few-mode fiber.

Based on the spatial profiles and polarization states evolution process of the first-order modes resulted from stress-induced birefringence in the few-mode fiber (FMF), we analyze the mapping relationship between the input polarization states represented on polarization PS and the output spatial profiles represented on the orbital PS of the FMF with respect to the magnitude and orientation of birefringence. When the input mode lobe orientation and the phase differences between the four eigenmodes of FMF induced by the stress birefringence satisfy a given condition, the mapping relationship between the input polarization PS and the output orbital PS is linear. Thus, the arbitrary points on the orbit PS can be generated at the output of stressed FMF by controlling the polarization state of the input modes. Then we experimentally verify that, an electrical single-mode polarization controller, a mode converter for converting fundamental mode to higher-order mode, a polarization controller mounting a coil of two-mode fiber and a polarizer can be employed to generate arbitrary first-order spatial modes on the orbital PS by controlling the input single-mode polarization states. The positions on the orbital PS of the generated first-order modes, which are obtained by calculating the three normalized Stokes parameters of output modes, agree well with the simulation ones. The correlation coefficients between the theoretical mode profiles and the experimental ones are higher than 80%. Since the spatial profile evolutions depend on the variations of the input polarization states, a potential advantage of this method is high-speed switching among desired first-order modes by using the commercial devices switching the state of polarization.

Long-range Raman distributed temperature sensor with high spatial and temperature resolution using graded-index few-mode fiber.

We designed and fabricated a graded-index few-mode fiber (GI-FMF) with large effective mode area and low intermodal dispersion for Raman distributed temperature sensor (RDTS) to simultaneously achieve high spatial and temperature resolution over long distance. In experiment, we measured the spatial and temperature resolution of the RDTS using different types of fibers under different launch conditions based on a commercially available RDTS system. By using the GI-FMF under the overfilled launch condition, we achieved a 1 °C temperature resolution with a spatial resolution of 1.13 m at the distance of 25 km. The spatial resolution using the standard MMF degraded to 2.58 m with only a 0.3 °C higher temperature resolution in comparison. As a result, the GI-FMF under the few-mode operation condition can provide a desirable temperature resolution comparable with that of the MMF with a negligible degradation on spatial resolution. Moreover, the RDTS using the GI-FMF under the quasi-single mode operation condition achieved a temperature resolution of 4.7 °C at the distance of 25 km with a 2.2 °C improvement and no degradation on spatial resolution compared with that using the standard SMF.

Multimode and single-mode fiber compatible graded-index multicore fiber for high density optical interconnect application.

We designed and fabricated a graded-index (GI) multicore fiber (MCF) compatible with both standard multimode and single-mode fiber for high density optical interconnect application in large-scale data centers. The proposed fiber supports long-distance multimode transmission at 850 nm as well as quasi-single mode transmission at 1310 nm and 1550 nm. The parameters of the GI-MCF have been optimized to obtain both a small differential mode delay at 850 nm and a small mode field diameter mismatch of less than 0.5 µm with single-mode fiber at 1310 nm and 1550 nm with a negligible inter-core crosstalk. In experiment, we successfully realized the multimode operation over 1 km-long GI-MCF at 850 nm and the quasi-single mode operation over 12.4 km-long GI-MCF at 1310 nm and 1550 nm at a data rate of 7×10-Gb/s. The multi-wavelengths multicore transmission was demonstrated for the first time. The experiment results imply that the proposed GI-MCF satisfies various requirements in such as operating wavelength, accessible distance and interconnect density of large-scale data center, and can effectively reduce the fiber numbers and system complexity.

Investigation of channel model for weakly coupled multicore fiber.

We investigate the evolution of the decorrelation bandwidth of intercore crosstalk (IC-XT) based on the modified mode-coupled equations (MCEs) in homogeneous weakly coupled multicore fibers (WC-MCFs). The modified MCEs are numerically solved by combining the fourth order Runge-Kutta method with the compound Simpson integral method. It can be theoretically and numerically observed that the decorrelation bandwidth of IC-XT decreases with transmission distance by fractional linear function. The evolution rule of IC-XT's decorrelation bandwidth is further confirmed by experiments, which can be used as an evaluation criterion for the channel model. Finally, we propose a new channel model with the coupling matrix of IC-XT generated directly from the phase transfer function (PTF), which is in good agreement with the above evaluation criterion. We believe the proposed channel model can provide a good simulation platform for homogeneous WC-MCF based communication systems.

Directional torsion and temperature discrimination based on a multicore fiber with a helical structure.

We propose and experimentally demonstrate a directional torsion sensor based on a Mach-Zehnder interferometer formed in a multicore fiber (MCF) with a ~570-µm-long helical structure (HS). The HS was fabricated into the MCF by simply pre-twisting and then heating with a CO2 laser splicing system. This device shows the capability of directional torsion measurement from -17.094 rad/m to 15.669 rad/m with the sensitivity of ~0.118 nm/(rad/m). Moreover, since the multiple interferences respond differently to torsion and temperature simultaneously, the temperature cross-sensitivity of the proposed sensor can be eliminated effectively. Besides, the sensor owns other merits such as easy fabrication and good mechanical robustness.

Performance enhancement of free-space optical communications under atmospheric turbulence using modes diversity coherent receipt.

This paper numerically and experimentally investigates the performance of free-space optical receiver using modes diversity coherent receipt under moderate-to-strong turbulence. By utilizing a three-mode photonic lantern with digital maximum ratio combining, a 40 Gbps QPSK optical signal is received. The turbulence strength is measured by the ratio of beam diameter to atmospheric coherence length, D/r0. The larger the D/r0, the stronger the turbulence is, and vice versa. Compared with conventional single mode fiber based receipt, the required transmitted power can reduce by 4.6 dB and 4 dB at 10% interruption probability under turbulence strength D/r0 = 8 and 16. The required transmitted power at bit error ratio of 2.2 × 10-2 can relax by 4.2 dB and 5 dB under turbulence strength D/r0 = 8 and 16.

Few-mode multicore fiber enabled integrated Mach-Zehnder interferometers for temperature and strain discrimination.

We proposed and experimentally demonstrated paralleled Mach-Zehnder interferometers (MZIs) in few-mode multicore fiber (FM-MCF) for temperature and strain discriminative sensing. A section of FM-MCF is sandwich-spliced between two single-mode multicore fiber (SM-MCF) with a rotational offset. The arbitrarily controlled angular misalignment generates intentional intermodal interferences in outer cores of the FM-MCF thus multiple MZI structures are implemented. Experimental results show that the temperature sensitivities are 105.8 pm/°C and 223.6 pm/°C for two outer cores, strain sensitivity is 13.96 pm/µÎµ for the outer core 1 and 11.7 pm/µÎµ for the outer core 2, respectively. Due to the low condition number of the cross coefficient matrix dependent on the temperature and strain response indexes, the temperature-strain cross sensitivity can be efficiently eliminated. In addition, the structure's fabrication process is simple, cost effective, and repeatable. The sensing structure can be applied to a wide range of measurements and is expected to develop potentials by building a higher dimensional matrix with more cores.

Real-time 100 Gbps/λ/core NRZ and EDB IM/DD transmission over multicore fiber for intra-datacenter communication networks.

A BiCMOS chip-based real-time intensity modulation/direct detection spatial division multiplexing system is experimentally demonstrated for both optical interconnects. 100 Gbps/λ/core electrical duobinary (EDB) transmission over 1 km 7-core multicore fiber (MCF) is carried out, achieving KP4 forward error correction (FEC) limit (BER < 2E-4). Using optical dispersion compensation, 7 × 100 Gbps/λ/core transmission of both non-return-to-zero (NRZ) and EDB signals over 10 km MCF transmission is achieved with BER lower than 7% overhead hard-decision FEC limit (BER < 3.8E-3). The integrated low complexity transceiver IC and analog signal processing approach make such a system highly attractive for the high-speed intra-datacenter interconnects.

All-fiber orbital angular momentum mode multiplexer based on a mode-selective photonic lantern and a mode polarization controller.

We demonstrate for the first time, to the best of our knowledge, an all-fiber orbital angular momentum (OAM) multiplexer that multiplexes both OAM modes of -l and +l up to the second order by using a mode-selective photonic lantern and a mode polarization controller. The experimentally obtained mode profiles are close to the theoretical results, and the mode purities are higher than 89% for all the OAM modes at 1550 nm. The losses for all mode generations are less than 3.8 dB in the C-band.

Link optimized few-mode fiber Raman distributed temperature sensors.

A link optimized few-mode fiber-based Raman distributed temperature sensor is proposed to enhance the temperature resolution of the long-distance sensing system. Comprehensive theoretical analysis and experimental validation in contrast with the traditional single-mode fiber-based sensing link have been conducted to reveal the benefits provided by the optimization scheme. The temperature resolutions are about 3.8°C for the proposed fiber link at 20 km distance, leading to about 6.2°C improvement compared with the single-mode fiber (SMF) link. The total measurement is completed within 80 s over 20 km with a spatial resolution of 3 m.

Design of highly mode group selective photonic lanterns with geometric optimization.

Highly mode group selective photonic lanterns (PLs) are desired for mode-division multiplexing transmission systems. Usually, mode selectivity is achieved by using input fibers with different core diameters or refractive indices to break degeneracy between mode groups. We demonstrate that mode group selectivity can be greatly improved by optimizing core geometry of PLs. For three-mode PLs with optimized core geometry, based on beam propagation method (BPM) simulation results, mode selectivity is improved from 23.8 dB to 43.9 dB for LP01 mode, and mode selectivity of LP11 mode is improved from 26.8 dB to 45.5 dB. The reason is the optimized core geometry can significantly slow down the changing of mode profile along the taper of the PL; thus adiabatic tapering requirement can be greatly alleviated. It can also be observed that the simulation results by the BPM are in good agreement with calculation of coupled-mode theory.