Search Results (596)

To improve the efficiency and stability of the system, this paper proposes a monolithic integrated optical path design for a cavity optomechanical accelerometer based on a 250 nm top silicon thickness silicon-on-insulator (SOI) wafer instead of readout through U-shape fiber coupling. Finite Element Analysis (FEA) and Finite-Difference Time-Domain (FDTD) methods are employed to systematically investigate the performance of key optical structures, including the resonant modes and bandgap characteristics of photonic crystal (PhC) microcavities, transmission loss of strip waveguides, coupling efficiency of tapered-lensed fiber-to-waveguide end-faces, coupling characteristics between strip waveguides and PhC waveguides, and the coupling mechanism between PhC waveguides and microcavities. Simulation results demonstrate that the designed PhC microcavity achieves a quality factor (Q-factor) of 2.26 × 10⁵ at a 1550 nm wavelength while the optimized strip waveguide exhibits a low loss of merely 0.2 dB over a 5000 μm transmission length. The strip waveguide to PhC waveguide coupling achieves 92% transmittance at the resonant frequency, corresponding to a loss below 0.4 dB. The optimized edge coupling structure exhibits a transmittance of 75.8% (loss < 1.2 dB), with a 30 μm coupling length scheme (60% transmittance, ~2.2 dB loss) ultimately selected based on process feasibility trade-offs. The total optical path system loss (input to output) is 5.4 dB. The paper confirms that the PhC waveguide–microcavity evanescent coupling method can effectively excite the target cavity mode, ensuring optomechanical coupling efficiency for the accelerometer. This research provides theoretical foundations and design guidelines for the fabrication of high-precision monolithic integrated cavity optomechanical accelerometers. Full article

Low-finesse Fabry–Perot (F–P) cavities, widely applied in the field of micro-displacement measurement, offer significant advantages in reducing the influence of higher-order reflections and improving the accuracy of measurement systems. Generally, an F–P cavity finesse of 0.5 is required to achieve high-precision micro-displacement measurements. However, in optical design, low-finesse cavities impose strict requirements on reflectivity, and maintaining fine stability during cavity movement is challenging. Achieving ideal orthogonal interference with a finesse of 0.5 thus presents considerable difficulties. This study proposes a novel low-finesse F–P cavity design that employs a high-reflectivity spherical reflector and the end face of a fiber collimator as the reflective surfaces of the cavity. By utilizing beam divergence characteristics and geometric parameters, a structure with a finesse of approximately 0.5 is quantitatively designed, enabling a simplified implementation without the need for angular alignment. Compared with conventional approaches, this method eliminates the need for precise angular alignment of the reflective surfaces, significantly simplifying implementation. The experimental results show that, under fixed receiving field angles and beam radii of the fiber collimators, ideal orthogonal interference can be achieved by selecting the radius of the reflective sphere. Under varying working distances, the average finesse values of the interference spectra measured by Collimators 1 and 2 are 0.496 and 0.502, respectively, both close to the theoretical design value of 0.5, thereby meeting the design requirements. Full article

By measuring the transfer function of the single-mode multi-aperture vertical-cavity surface-emitting laser (SM MA VCSEL) transmitting over a long single-mode fiber at 850 nm, we confirm that the chirp of the SM MA VCSEL under study is dominated by transient chirp with an alpha value of −3.81 enabling a 19 GHz bandwidth over 10 km of single-mode fiber. The detailed measurement of the VCSEL with different bias currents also allows us to recover other key characteristics of the VCSEL, thereby enabling us to practically construct the optical eye diagrams that closely match the experimentally measured ones. The link-level transfer function can be obtained using an analytical equation including effects of modal dispersion and laser chirp–chromatic dispersion (CD) interaction for an MMF of a given length and bandwidth grade. The narrow linewidth and chirp characteristics of the SM MA VCSEL enable transmission performance that surpasses that of conventional MM VCSELs, achieving comparable transmission distances at moderate modal bandwidths for OM3 and OM4 fibers and significantly longer reaches when the modal bandwidth is higher. The transmission performance was also confirmed with the modeled eye diagrams using extracted VCSEL parameters. The chirp properties also provide sufficient bandwidth for SM MA VCSEL transmission over kilometer-scale lengths of single-mode fibers at a high data rate of 100G or above with sufficient optical power coupled into the fibers. Advanced transmission distances are possible over multimode and single-mode fibers versus chirp-free devices. Full article

The objective of this study is to investigate the degradation characteristics of oat grass in the rumen of Mindong goats and changes in microbial community attached to the grass surface. Four healthy male goats, aged 14 months, with permanent rumen fistula, in eastern Fujian, were selected as experimental animals. The rumen degradation rate of oat grass was measured at 4, 12, 24, 36, 48, and 72 h using the nylon bag method. Surface physical structure changes in oat grass were observed using scanning electron microscopy (SEM), cellulase activity was measured, and bacterial composition was analyzed using high-throughput 16S rRNA gene sequencing technology. The findings of this study indicate that oat grass had effective degradation rates (ED) of 47.94%, 48.69%, 38.41%, and 30.24% for dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), and acidic detergent fiber (ADF), respectively. The SEM was used to investigate the degradation process of oat grass in the rumen. After 24 h, extensive degradation of non-lignified tissue was observed, resulting in the formation of cavities. At 36 h, significant shedding was observed, and by 72 h, only the epidermis and thick-walled tissue, which exhibited resistance to degradation, remained intact. Surface-attached microorganisms produced β-GC, EG, CBH, and NEX enzymes. The activity of these enzymes exhibited a significant increase between 4 and 12 h and showed a positive correlation with the degradation rate of nutrients. However, the extent of correlation varied. Prevotella and Treponema were identified as key genera involved in the degradation of roughage, with their abundance decreasing over time. Principle Coordinate Analysis (PCOA) revealed no significant differences in the rumen microbial structure across different time points. However, Non-Metric Multidimensional Scaling (NMDS) indicated a discernible diversity order among the samples. According to the Spearman correlation coefficient test, Ruminococcus, Fibrobacter, and Saccharoferments exhibited the closest relationship with nutrient degradation rate and surface enzyme activity, displaying a significant positive correlation. In summary, this study delineates a time-resolved correlative framework linking microbial succession to structural and enzymatic dynamics during oat grass degradation. Full article

Titanium alloy/carbon fiber-reinforced polymer (TA1/CFRP) laminates, representing the latest fourth generation of fiber metal laminates (FMLs), is a kind of high-performance composite material. However, the fragility of the fiber/resin and metal/resin interface layers in these composites directly impacts their mechanical properties. To enhance these properties, this paper investigates the preparation process of multi-walled carbon nanotube (MWCNT)-reinforced ultra-thin TA1/CFRP laminates and explores the impact of MWCNT content on the interlayer properties of these ultra-thin TA1/CFRP laminates. Initially, the challenge of dispersing carbon nanotubes using ultrasonic dispersion devices and dispersants was addressed. Vacuum-curing pressure studies revealed minimal overflow at 0.8 bar vacuum. Subsequently, the impact of MWCNT content on interlayer properties was investigated. The results indicated a significant increase in interlayer shear strength and interlayer fracture toughness with MWCNT additions at 0.5 wt% and 0.75 wt%, whereas the interlayer properties decreased at 1.0 wt% MWCNT. Fracture morphology analysis revealed that MWCNT content exceeding 0.75 wt% led to agglomeration, resulting in resin cavity formation and stress concentration. Full article

This study consisted of the injection molding simulation of polycaprolactone (PCL)-based nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs) for biomedical implant manufacturing. The simulation was additionally supported by experimental validation. The influence of varying MWCNT concentrations (0.5%, 5%, and 10% by weight) on key injection molding parameters, i.e., melt flow behavior, pressure distribution, temperature profiles, and fiber orientation, was analyzed with SolidWorks Plastics software. The results proved the low CNT content (0.5 wt.%) to be endowed with stable filling times, complete mold cavity filling, and minimal frozen regions. Thus, this formulation produced defect-free modular filament sticks suitable for subsequent 3D printing. In contrast, higher CNT loadings (particularly 10 wt.%) led to longer fill times, incomplete cavity filling, and early solidification due to increased melt viscosity and thermal conductivity. Experimental molding trials with the 0.5 wt.% CNT composites confirmed the simulation findings. Following minor adjustments to processing parameters, high-quality, defect-free sticks were produced. Overall, the PCL/MWCNT composites with 0.5 wt.% nanotube content exhibited optimal injection molding performance and functional properties, supporting their application in modular, patient-specific biomedical 3D printing. Full article

We demonstrate a novel bidirectional mode-locked ultrafast fiber laser based on an asymmetric dual-cavity architecture that enables freely tunable repetition rate differentials at the kilohertz level, while maintaining inherent common-mode noise suppression through precision thermomechanical stabilization. Through cascaded amplification and nonlinear temporal compression, we obtained bidirectional pulse durations of 33.2 fs (clockwise) and 61.6 fs (counterclockwise), respectively. The developed source demonstrates exceptional capability for asynchronous optical sampling applications, particularly in enabling the compact implementation of real-time measurement systems such as terahertz time-domain spectroscopy (THz-TDS) systems. Full article

Vertical-cavity surface-emitting laser (VCSEL)-based transmission over multimode fiber (MMF) has achieved data rates of 100G per lane and is progressing towards 200G/lane, which demands more modal bandwidth from MMF to ensure adequate transmission reach. We address the needs of higher modal bandwidth from the point of view of engineering VCSEL launch conditions. We explore the options for using subsets of 10 standard-based launch conditions by analyzing the measured encircled fluxes from commercial VCSEL transceivers over two options. By utilizing experimentally measured MMF data, we demonstrated a significant improvement in modal bandwidth with these options. The launch conditions also impact the wavelength dependence of modal bandwidth for VCSELs operating at wavelengths longer than 850 nm. We conducted detailed Monte Carlo simulation of the wavelength dependence of modal bandwidth over MMFs. For one launch condition option using a smaller area, the modal bandwidths are improved over the effective modal bandwidth (EMB), and favor very high data rate transmission by allowing the use of a smaller area photodetector. Full article

A dual-parameter optical fiber sensor for measuring the magnetic field and temperature based on the Fabry–Perot interferometer (FPI) and magnetic polymer film was proposed and designed, realizing dual-parameter measurement of temperature and the magnetic field. The sensor uses the excellent elasticity and thermal expansion coefficient of PDMS and the magnetostrictive effect of Fe₃O₄ magnetic polymer film to provide magnetic field and temperature detection while maintaining good reusability, achieving a magnetic field sensitivity and temperature sensitivity of 69 pm/mT and 390 pm/K, respectively. The sensor has the advantages of a low cost, a simple manufacturing process, good linearity, and a sensitive temperature response. It has broad application prospects in medicine, geography, aerospace, and other fields. Full article

Fiber-reinforced composites (FRCs) are recognized for enhancing the fracture resistance of structurally compromised teeth. However, the optimal orientation and placement of fibers in direct resin composite restorations remain under debate. This study aimed to evaluate the fracture resistance of maxillary premolars with mesio-occluso-distal (MOD) cavities restored using polyethylene fibers with different placement techniques, compared to conventional incremental composite restoration. Methods: Sixty intact maxillary premolars were randomly assigned to six groups (n = 10). Group 1: intact teeth (positive control); Group 2: MOD cavity without restoration (negative control); Group 3: MOD cavity restored with nanohybrid composite using the incremental technique; Group 4: polyethylene fiber placed on the pulpal floor; Group 5: fiber placed circumferentially along cavity walls (wall-papering technique); Group 6: fiber placed buccolingually in an occlusal groove (occlusal splinting). Fracture resistance was assessed using a universal testing machine. Failure mode was also analyzed. Results: Group 6 (occlusal splinting) exhibited the highest fracture resistance (1137.72 ± 316.20 N), significantly exceeding Group 3 (546.93 ± 59.89 N) and other fiber-reinforced groups (p < 0.05). Failure mode analysis revealed no significant differences between the fiber-reinforced groups and the intact teeth. Group 6 also had the highest percentage of restorable fractures (90%). Conclusions: Incorporating polyethylene fibers, especially through occlusal splinting, significantly improves fracture resistance in MOD-restored maxillary premolars. This technique may offer a promising alternative to conventional composite restorations in structurally weakened posterior teeth. Full article

In the aerospace, energy and nuclear energy sectors, dynamic pressure measurement of power equipment and pressure vessels in high-temperature environments is critical for validating design, manufacturing processes and operational condition monitoring. The existing electric sensors are resistant to temperature. It is difficult to meet the pressure measurement requirements of high temperature and high-frequency responses. In this paper, combining the material properties of high-temperature co-fired ceramics (HTCC) with the structural characteristics of Fabry–Perot, an all-ceramic fiber-optic Fabry–Perot high-temperature pulsating pressure sensor based on a HTCC pressure- sensing diaphragm and ceramic high-temperature sintering process, is proposed. Experimental results show that in the pressure range of 6 MPa, the static pressure sensitivity of the sensor is 1.30 nm/MPa, and the linear goodness of fit reaches 0.99913. The dynamic response frequency of the sensor reaches 598.5 kHz. The survival time at high temperature of 800 °C is more than 80 h. The sensitivity to temperature is 0.00475 nm/°C. Full article

This paper reports and demonstrates, for the first time, a Mach–Zehnder interferometer (MZI) sensor for refractive index (RI) detection based on a rice-shaped air cavity (RAC). In this design, RACs are inserted on both sides of a no-core fiber (NCF), functioning as a beam expander and receiver. When the input light enters the NCF through the RAC, it is fully excited from the fundamental mode to higher-order modes within just 500 μm of propagation. This enables the sensor to achieve exceptionally high sensitivity in external RI detection. By adjusting the width of the RAC, the RI sensitivity can be effectively tuned. When the RAC measures 30.6 × 70 μm, the two selected transmission peaks reach maximum RI sensitivities of 1550.41 nm/RIU and 1810.89 nm/RIU, respectively. Notably, the total length of the sensor is only 0.64 mm, offering a promising approach for the development of ultra-compact RI sensors in the future. Full article

In this paper, a MgO-based high-temperature Fabry-Perot (F-P) vibration sensor with a fiber-optic collimator is proposed and experimentally demonstrated at 1000 °C. The sensor is composed of a sensing unit and a fiber-optic collimator. The F-P cavity is formed by the upper surface of the inertial mass block and the countersunk hole of the cover layer. The length of the F-P cavity changes with external vibrations. The sensing unit is prepared by wet etching technology and three-layer direct bonding technology, which ensure its stability and reliability in high-temperature environments. The experimental results indicate that the sensor can operate stably within a range from room temperature up to 1000 °C. The sensitivity and non-linearity of the sensor at 1000 °C are 1.3224 nm/g and 3.8%, respectively. Furthermore, the sensor operates at frequencies of up to 4 kHz while remaining unaffected by lateral vibration signals. The high-temperature F-P vibration sensor can effectively deal with the fiber damage in extreme environments and exhibits considerable potential for widespread applications. Full article

This study presents a novel ion-imprinted fiber material, I-(PP-g-GMA-NMDG), designed for the rapid and selective adsorption of borate ions. Leveraging low-temperature plasma graft polymerization, polypropylene (PP) melt-blown fibers were functionalized with glycidyl methacrylate (GMA) and N-methyl-D-glucamine (NMDG) to introduce tailored recognition sites. Systematic optimization of plasma parameters (100 W discharge power, O₂ atmosphere) and liquid-phase grafting conditions (28.5% GMA, 85 °C, 2.5 h) achieved a grafting rate of 203.26%. The imprinted fibers exhibited exceptional adsorption performance, with a maximum capacity of 35.85 mg/g at pH 9, reaching 90% saturation within 60 min. Adsorption kinetics adhered to a pseudo-second-order model, while the Freundlich isotherm indicated multilayer adsorption. Competitive ion experiments demonstrated high selectivity for B(OH)₄⁻ over anions (SO₄²⁻ and Cl⁻) and cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺), which was attributed to the precise spatial and charge complementarity of the imprinted cavities. Characterization via FT-IR, XRD, and SEM confirmed successful synthesis and structural stability. The material retained 78.1% adsorption efficiency after five regeneration cycles, showcasing its practicality for boron recovery from wastewater. This work advances boron-selective adsorption technology by combining plasma modification with ion imprinting, offering a sustainable solution for industrial and environmental applications. Full article

This study presents the synthesis of manganese molybdenum tetraoxide (MnMoO₄)-based nanoparticles and then their experimental demonstration as saturable absorbers (SAs) in erbium-doped fiber lasers (EDFLs). The MnMoO₄ nanoparticles were prepared and then embedded between the fiber ferrule to act as an SA to generate Q-switched pulsed operation in EDFLs. For the characterization, scanning electron microscopy (SEM) was employed to confirm the particle size of the prepared MnMoO₄ nanoparticles, and the SA optical properties were further investigated by measuring their modulation depth and saturation intensity. By implementing the prepared SA within the cavity, the measured results revealed that under pump power ranging from 28 to 312.5 mW, the laser exhibited Q-switched pulse durations varying from 15.22 to 2.35 µs and repetition rates spanning from 24.98 to 88.11 kHz. The proposed EDFL system delivered an average output power between 0.128 and 2.95 mW, pulse energies ranging from 5.12 to 33.49 nJ, and peak power from 0.281 to 6.26 mW. The laser stability was also confirmed by continuously noticing the pulse duration, emission wavelengths, and pulse repetition rates for 4 h. Finally, a numerical model based on a nonlinear Schrödinger equation (NLSE) was employed to validate both experimental and theoretical results of the passive Q-switched EDFL. These findings highlight the potential of EDFLs utilizing MnMoO₄-based SAs for potential applications in pulsed laser sources. Full article