Search Results (2,235)

Reliable communication infrastructure is a fundamental component of Intelligent Transport Systems (ITSs), particularly in scenarios involving maritime corridors and emergency traffic management. In locations where optical fiber deployment is geographically constrained, unmanned aerial vehicle (UAV)-assisted free-space optical (FSO) relay links provide a flexible and rapidly deployable alternative. However, atmospheric attenuation, turbulence-induced fading, and wind-induced UAV misalignment can severely degrade link reliability and disrupt real-time transport data streams. This study proposes a payload-efficient multiple-input multiple-output free-space optical (MIMO-FSO) relay architecture based on a multi-output/single-input (MOSI) uplink and a single-output/multi-input (SOMI) downlink. Here, MOSI denotes multiple ground-based transmit apertures directed toward a single UAV receiving aperture, whereas SOMI denotes one UAV transmitting aperture serving multiple ground-based receiving apertures. Unlike conventional symmetric UAV-assisted MIMO-FSO relays that may duplicate diversity hardware on the aerial node, the proposed design shifts the parallel optical branches to the ground stations and keeps only one optical receiver and one optical transmitter on board the UAV. Under the adopted 4 × 4 comparison assumption, this reduces the UAV-side optical branch count from eight to two, corresponding to a 75% branch-count reduction proxy. System performance is evaluated over a 1.54 km relay link. The analytical framework describes Beer–Lambert attenuation, log-normal/gamma–gamma turbulence, and statistical pointing errors; in the OptiSystem implementation, their combined effects are represented by equivalent aggregate losses of 25 dB/km for atmospheric absorption/scattering and 25.5 dB/km for turbulence- and pointing-related degradation. Comparative simulations for SISO, 2 × 2, and 4 × 4 configurations show that the proposed 4 × 4 architecture increases the Q-factor from 8.38 to 18.25 and changes the OptiSystem-reported minimum BER from 2.73 × 10⁻¹⁷ to 9.95 × 10⁻⁷⁵. Because a finite simulation cannot statistically validate error probabilities of this magnitude through raw error counting, values far below 10⁻¹² are interpreted primarily as comparative indicators of receiver decision margin. The findings provide simulation-based evidence that the proposed architecture is a scalable candidate for resilient optical wireless backhaul in smart transport corridors under adverse propagation conditions. Full article

This paper presents a differential capacitive horizontal pendulum tiltmeter based on electrostatic feedback force. The system mainly consists of a horizontal pendulum bob, a triangular platform, a pendulum locking motor, a differential capacitive sensing circuit, an electrostatic feedback circuit, and a sealed protective housing. The electrostatic feedback differential capacitive horizontal pendulum tiltmeter does not introduce a novel tilt measurement principle; its pendulum still adopts the classic Zöllner double-suspension-wire configuration. In this study, engineering improvements were implemented on the conventional quartz horizontal pendulum tiltmeter by replacing quartz fibers with tungsten wires, substituting optical lever sensors with capacitive sensors, and incorporating the electrostatic feedback principle. The improved tiltmeter features a compact structure and reduced size, which greatly facilitates deployment and installation while significantly enhancing practical applicability. Moreover, it overcomes the drawback of conventional horizontal pendulums—namely, that the scale factor varies with inclination and requires frequent calibration—and thus holds considerable importance for geophysical ground deformation observation. Full article

Following the integrated optical assembly and single printed circuit board co-layout design concept for electrical circuits, this paper develops a field-programmable gate array (FPGA) based, miniaturized, eight-channel microwave photonic transceiver stabilization system for the joint regulation of lasers and Mach–Zehnder modulators (MZMs). The integrated single-board hardware enables high-precision, high-reliability automatic temperature control (ATC), automatic power control (APC), and arbitrary closed-loop control of the MZMs bias point, overcoming the drawbacks of discrete single-channel, independent control schemes reported in previous works, which lack expandability for large radar arrays. The laser sub-module supports continuously adjustable drive current and multi-level protection, achieving wavelength stability of 0.01 nm and an output optical power fluctuation of less than 0.02%. The MZM control unit delivers wide-range, high-stability bias drift suppression with arbitrary bias point stability up to 0.05 dB. All static and dynamic performance indicators of the proposed module are characterized using a dedicated experimental setup comprising optical power meters, optical spectrum analyzers, temperature cycling chambers, and vector signal analyzers. Leveraging FPGA-based parallel hardware logic, the system features low latency, low jitter, cross-channel mismatch compensation, and excellent timing synchronization, with a compact overall footprint of 180 mm × 120 mm that matches the size of radar antenna panels and supports flexible array scaling. The proposed integrated module meets the low-noise, high-reliability, and high-integration requirements of radio-over-fiber links in microwave photonic radars. It effectively advances the practical engineering deployment of microwave photonic radar systems. Full article

This paper proposes a high-sensitivity and sensitivity-tunable vibration sensing system based on a switchable loop length optoelectronic oscillator (OEO). Carrier-sideband separation is realized by using an acousto-optic modulator (AOM), and the resonant cavity length is designed to be independent of the sensing fiber arm. Compared with a conventional 10 GHz OEO under the same total loop delay condition, the proposed architecture provides a theoretical sensitivity enhancement of approximately $1.93\times {10}^4$, without requiring a high RF oscillation frequency. Meanwhile, the system oscillates at only 80 MHz, which greatly reduces the implementation difficulty of the frequency detection circuit. The proposed scheme further introduces a mechanical optical switch (MOS) to select intra-loop fibers of different lengths, thereby reconfiguring the equivalent loop delay and the free spectral range of the OEO. Experimental results show that stable single-mode oscillation is achieved at 80.42 MHz with a side-mode suppression ratio of 51 dB. By selecting loop fiber lengths of 1200 m, 500 m and 0 m, frequency-to-displacement sensitivities of 0.892 GHz/cm, 1.93 GHz/cm and 9.27 GHz/cm are obtained respectively, with excellent linearity. A 600 Hz vibration signal is successfully demodulated with a signal-to-noise ratio of 72.1 dB. The proposed method provides a simple and reconfigurable solution for high-precision vibration measurement under different operating conditions. Full article

Optical fiber multi-analyte biosensors have become an important cutting-edge technology for the simultaneous detection of multiple biochemical substances in complex samples due to their unique advantages such as small size, anti-interference capability, and remote and label-free detection. This paper systematically reviews the recent research progress of optical fiber multi-analyte biosensors in the field of simultaneous detection of various types of targets. The review is organized by detection target type and elaborates on the simultaneous detection of biomarkers and proteins, viruses and bacteria, biological metabolites and nutrients, heavy metal ions, gases, organic pollutants, cells, and mixed detection of different types of biochemical substances. The advantages and disadvantages of existing optical fiber multi-analyte biosensors are summarized. Key technical challenges are also discussed, including issues of selectivity, long-term stability, real-sample validation, and system integration that currently hinder practical deployment. Finally, the future challenges and development directions of optical fiber multi-analyte biosensors are briefly discussed, providing references for relevant research teams. Full article

Glaucoma is a chronic, progressive optic neuropathy and the second leading cause of irreversible blindness worldwide. Although elevated intraocular pressure (IOP) remains the principal modifiable risk factor, it is neither necessary nor sufficient for disease development. The literature indicates that systemic conditions such as obstructive sleep apnea (OSA) may contribute to its pathogenesis. The pathophysiology of glaucoma is supported by several theories, primarily the mechanical and vascular theories. This review describes the pathophysiological links between OSA and glaucoma considering current theories. The principal connecting mechanism appears to be chronic intermittent hypoxia and reduced ocular perfusion pressure, which trigger optic nerve head hypoxia, oxidative stress, and biomechanical remodeling of the lamina cribrosa. These processes interact within a vicious cycle that progressively compromises the metabolic support of optic nerve axons. The mechanisms described are particularly relevant to normal-tension glaucoma, which may be associated with OSA. Retinal nerve fiber layer thinning appears among the earliest markers of optic nerve vulnerability, whereas IOP and visual field changes are more variable. These observations underscore the clinical relevance of the OSA–glaucoma relationship and support a multidisciplinary approach incorporating routine ophthalmic screening for subclinical optic nerve damage. Full article

Industrial automation and the Internet of Things (IoT) are driving demand for optical access networks capable of supporting massive connectivity with deterministic low latency. Conventional passive optical networks (PONs) face scalability and cost limitations in ultra-dense deployment scenarios. Here we propose and experimentally demonstrate a polarization-carrier dual-reuse coherent orthogonal frequency division multiplexing PON (CO-OFDM-PON) architecture enabled by optical frequency comb (OFC) sources. The design maps data and carrier signals onto orthogonal polarization states. This enables carrier reuse for both downstream coherent detection and upstream transmission through injection-locked laser (ILL)-based carrier regeneration at the optical network unit (ONU). We comprehensively characterize the key subsystems. These include the OFC, ILL, and erbium-doped fiber amplifier (EDFA). This ensures stable multi-wavelength generation, carrier regeneration, and enhanced receiver sensitivity under high split ratios. Through simulation and experimental analysis of fiber nonlinearities in industrial PON scenarios, we identify an optimal per-channel launch power of 4 dBm. This power balances sensitivity and link budget requirements. Scalability analysis for standard PON reach is also provided. The system demonstrates 16-channel 100 Gb/s per wavelength downstream 16-QAM OFDM transmission. The link budget exceeds 34 dB with bit error rates (BERs) below the forward error correction (FEC) threshold of 1 × 10⁻². While the coherent ONU architecture offers superior spectral efficiency, it entails higher component costs than direct-detection alternatives due to the required coherent receiver and polarization management components. Full article

The integration requirements of laser ranging, imaging, and communication functions in space target detection have placed higher demands on system performance. This paper takes a modularly designed integrated laser ranging, imaging, and communication system as an example and proposes a light source integration scheme based on fiber phased array beam splitting–coupling technology, effectively enhancing the system’s integration level and compactness. The system employs a Cassegrain optical system and beam splitting structure to achieve functional integration of laser communication, ranging, and polarization imaging. Ground experiments were conducted to evaluate the functional feasibility of the proposed integrated architecture. The visible light polarization imaging experiments at kilometer-level distances demonstrate that polarization-derived information can improve target–background separability under haze and low-contrast conditions. The UAV-based dynamic ranging experiment verifies that the system can acquire, track, and range a moving cooperative target under the tested field conditions, with the measured results being consistent with the designed meter-level ranging requirement. In addition, a 1 km coherent free-space laser communication experiment achieved 20 Gbps QPSK signal transmission with a bit error rate on the order of 10⁻⁷. These results provide experimental support and design references for integrated optoelectronic terminals used in space target observation, space debris monitoring, and related long-distance sensing and communication applications. Full article

This article proposes and experimentally demonstrates a covert key distribution scheme based on the phase fluctuation of a gain-switched laser diode (GSLD). The gain-switched pulse is used to generate the covert signal through spectral broadening and temporal spreading. The amplified spontaneous emission (ASE) light is used to generate ASE noise in the public channel. Eavesdroppers cannot perceive signals hidden in the public noise. The experimental results show that the correlation coefficient of the key waveforms reaches 0.95, and the scheme’s key generation rate (KGR) reaches 1.88 Gbit/s through a 25 km single-mode fiber (SMF). Moreover, the binary bitstreams have passed the NIST statistical test suite. The covert key distribution scheme proposed in this article provides an efficient way for the method of “one-time-pad” key distribution in high-speed optical communication systems. Full article

Saturable absorbers (SAs) are critical for passive mode-locking in ultrafast fiber lasers. Although many materials have been studied as SAs, new candidates with broadband and stable performance are still needed. In this work, we report the synthesis and fabrication of Ti₂O-based SAs and present the first systematic investigation of their performance in broadband ultrafast fiber lasers. Specifically, phase-pure Ti₂O crystals were synthesized via solid-state sintering. High-performance Ti₂O SAs were then fabricated through a photodeposition method. The balanced synchronous twin-detector measurement method demonstrated that Ti₂O exhibited obvious and stable saturable absorption behavior. To validate their broadband mode-locking capability, the as-prepared Ti₂O SAs were integrated into the Yb-doped and Er-doped fiber lasers, respectively. Experimental results show that both laser systems deliver stable pulsed output, with pulse durations of 441.7 ps at 1 μm and 522.5 fs at 1.5 μm. This work pioneers the application of Ti₂O in ultrafast photonics, and provides an important reference and novel research insights for the design and development of advanced broadband optical devices and systems. Full article

Fiber-reinforced polymers such as basalt fiber-reinforced polymers (BFRP) can be used in structural parts, which often require assembly operations. Thus, the surface quality after drilling operations is especially important. BFRP laminates have been drilled with three different tools, and their profile roughness and surface roughness have been evaluated by analyzing the following variables: average roughness (Ra), maximum height of profile (Rz), arithmetic mean height (Sa) and maximum height (Sz), by means of an optical system. The optical measurement of surface roughness has been hampered by fiber breakage. A statistical analysis has allowed for developing a general linear model that predicts the values of variables. The fitted model for Ra and Rz has a variation coefficient of 97.00% and 95.58% respectively, while that 91.74% and 68.02% for Sa at the inlet hole and outlet hole respectively; and 86.08% and 82.22% for Sz at the inlet hole and outlet hole respectively. Additionally, different machine learning regression algorithms have been applied using different configurations to establish prediction models of the main rugosity parameters. In this way, linear methods, Gaussian regression methods, Support Vector Machines, and fine trees have been applied using the rotation speed, feed rates, and tool as features. Also, a neural network has been optimized and applied for the same goal. The methods yielded satisfactory prediction results within the tested experimental domain for some roughness parameters. Although the behavior of all variables is similar across all drill bit types, drill bits with a point angle of 120° provided better results. Full article

Parallel shield tunneling in close proximity to existing metro tunnels induces additional settlement deformation of existing structures, which poses a challenge to operational safety. In this paper, a self-developed Φ200 mm model shield machine test system is adopted to carry out model test research on the settlement response of existing tunnels induced by parallel symmetric shield tunneling. A 1:30-scaled 3D-printed refined assembled segment model is fabricated based on similarity theory, and high-precision distributed optical fiber sensing technology is used for deformation monitoring. The influences of vertical spacing of tunnels, center spacing of new tunnels, axis angle and stratum loss rate on the settlement of existing tunnels are analyzed. The results show that the settlement curve of the existing tunnel arch presents a normal distribution shape, and the maximum settlement occurs near the new tunnel side. The settlement of existing tunnels decreases with the increase in vertical spacing between new and existing tunnels, and increases with the increase in stratum loss rate and center spacing of new tunnels. The research results can provide experimental support for safety control of parallel shield tunnel construction. Full article

Distinguishing between human-made interferences and natural background disturbances is of great significance for the safe operation of terrestrial optical cables because human-caused damage can be halted through timely intervention. To address the problem of small-sample disturbance recognition in distributed acoustic sensing (DAS) systems, this paper proposes a fused CNN–SVM classification model based on hybrid features. A convolutional neural network is employed to extract the high-level spatiotemporal features of disturbance signals, which are subsequently fused with statistical features and fed into a support vector machine for classification. Evaluated on open-source data, the proposed model achieves accuracy improvements of 9.1%, 8.7%, and 2.7% over the conventional CNN, the statistical-feature-based SVM, and the conventional CNN-SVM model, respectively. Furthermore, based on field-measured data, a dataset comprising 5664 samples was constructed, covering four typical disturbance-event types: background noise, drilling, knocking, and digging. The field classification results demonstrate that the three-layer convolutional structure of the model achieves a recognition accuracy of 98.5%. Both the ROC curves and multiple evaluation metrics indicate that the proposed three-layer fused CNN–SVM model delivers better classification performance and more balanced category recognition, offering a feasible reference for similar fiber disturbance engineering tasks. Full article

A portable OCT scanner usable for dental applications is designed to be compact (B4 notebook size), lightweight, and capable of DC battery operation, enabling chairside use and mobility in home medical care. TD-OCT faces the challenge of a slower measurement speed compared to SD/SS-OCT. In this study, by utilizing multiple rotating reflectors and combining them with a 3 × 3 fiber coupler, a measurement range of over 10 mm and a measurement speed of 1000 scans per second were achieved. Additionally, the dental intraoral probe was designed to ensure high accessibility, allowing free positioning within the oral cavity, with an ingeniously compact optical system. A cylindrical probe with a diameter of 6 mmϕ and a length of 10 mm was developed to enable tooth measurement. This study demonstrated the capability to evaluate attenuation coefficients derived from material properties, starting with measurements of caries and gums. Full article

The fractional Whitham–Broer–Kaup model governs nonlinear wave propagation in memory-dependent media, including porous structures, viscoelastic fluids, and irregular seabeds, yet the full dynamical spectrum from quasi-periodicity to deterministic chaos, the role of stochastic forcing, and reliable identification from noisy data remains insufficiently explored, particularly how the fractional order $\beta$ influences these regimes. This study addresses these gaps through a comprehensive, multi-method dynamical analysis of a representative nonlinear oscillator embodying key FWBK features. Three-dimensional attractor visualizations, return maps, and surrogate data tests demonstrate a transition from quasi-periodic toroidal attractors to fully developed chaos via torus breakdown, confirming that observed complexity originates from deterministic nonlinearity. Poincaré sections reveal multistability and KAM-type structures, where coexisting attractors depend on initial conditions, while increasing noise progressively disrupts coherent dynamics. The OGY control method effectively stabilizes unstable periodic orbits across chaotic regimes with minimal perturbation, and Lyapunov analysis indicates that stochastic forcing attenuates chaos while enhancing dissipation. The Fokker–Planck framework shows that noise reshapes probability landscapes, driving transitions from unimodal to bimodal distributions. Comparative analysis of SINDy, JMAP and VBA highlights trade-offs in interpretability, computational efficiency, and uncertainty quantification, while an integrated Bayesian–PCE–Sobol approach quantifies parametric uncertainty and reveals time-dependent sensitivity variations. Additionally, the overlapping of soliton solutions extracted via the enhanced modified Sardar sub-equation method reveals structural relationships among soliton families and their stability under interaction. Soliton branches that maintain high overlap under noise correspond to stable regimes, while those losing coherence indicate the onset of chaos. Furthermore, while the reduced dynamics in $\eta$-space are independent of $\beta$, the fractional order controls spatial compression and temporal scaling in physical coordinates, directly influencing observable wave localization. These results imply that fractional effects can modify chaos transitions, support controllability through OGY, and influence noise–instability interactions depending on $\beta$. This framework provides a robust, transferable methodology for analyzing and controlling nonlinear oscillatory systems under deterministic and stochastic conditions, with direct applications to FWBK-based models in coastal engineering, fiber optics, and quantum interference systems. Full article