Search Results (110)

Low-dimensional materials (LDMs) are often favored by researchers in the ultrafast photonics field for their low optical loss, ultrafast carrier response, broadband nonlinear absorption, and easy integration with optoelectronic systems. High-performance broadband saturable absorbers (SAs) fabricated from LDMs have become core components for achieving compact and miniaturized ultrafast laser. This paper systematically reviews the laser applications of LDM SAs in the near/mid-infrared spectral region, focusing on the pulse modulation mechanisms, material systems, and device integration approaches. It analyzes current research progress and challenges while outlining future development trends for LDM SAs in ultrafast pulsed lasers and optoelectronic devices. Full article

This paper investigates the problems of anti-synchronization for a class of inertial neural networks (INNs) with time-varying delays under the influence of deception attacks and hybrid triggered control. A novel dynamic hybrid-triggered control (DHTC) scheme is developed to utilize communication resources and enhance network security efficiently for the model INNs. By integrating the extended dissipative approach with Lyapunov–Krasovskii functional (LKF) techniques, new sufficient conditions are established to ensure the quadratic stability of the resulting closed-loop system. The proposed framework not only unifies the anti-synchronization problems but also extends classical passivity, (Q, S, R)-dissipative, $H_{\infty }$, and $L_2-L_{\infty }$ results as special cases. Moreover, the DHTC mechanism dynamically switches between time-triggered and event-triggered modes, reducing unnecessary signal transmissions while maintaining system stability against deception attacks. Finally, simulation results on delayed INNs demonstrate the effectiveness and superiority of the proposed theoretical and control strategy. Full article

Wireless power transfer (WPT) systems for electric vehicles (EVs) are increasingly being studied in the MHz range to increase power density and reduce the size of passive components. However, operation at higher frequencies significantly changes electromagnetic interference (EMI) behaavior. Fast switching in SiC- and GaN-based inverters, high-Q resonant operation, and frequency-dependent parasitic capacitances create conductive, capacitive, and magnetic interference mechanisms that are less significant in conventional kHz-range systems. Although many existing studies focus on power-transfer efficiency and converter optimization, EMI mechanisms in MHz-range EV WPT systems remain insufficiently systematized from a system-level electromagnetic perspective. This paper presents a state-of-the-art review of EMI generation mechanisms and system-level effects in high-frequency WPT systems for electric vehicles. The review considers the main interference sources and coupling paths, including switching-induced common-mode currents, resonant amplification of current and voltage stress, capacitive coupling between the coupler and nearby conductive structures, and magnetic-field redistribution caused by coil misalignment. Special attention is given to the transition from lumped-element assumptions to more distributed electromagnetic behavior at higher frequencies. The review also discusses the possible impact of these mechanisms on vehicle electronic subsystems and highlights the need for frequency-aware electromagnetic design, integrated modeling, and more rigorous EMC assessment for reliable MHz-range wireless EV charging systems. Full article

Cooperative multi-UAV path planning under dynamic and adversarial conditions demands simultaneous satisfaction of safety, efficiency, and coordination constraints, yet existing swarm-intelligence and RL–swarm hybrids rely on deterministic switching rules, tabular states, and ad hoc training schedules. This paper proposes RL-JSO, a hybrid framework in which a dueling double deep Q-network with prioritized experience replay adaptively selects among the drift, passive, and active phases of a jellyfish search optimizer, replacing the deterministic time-control rule with a learned policy. The framework integrates a five-layer hierarchical safety control mechanism, a mastery-gated nine-stage curriculum, and a shared reward module that architecturally enforces fairness between RL-JSO and a paired RL-PSO counterpart. Evaluation across four progressive campaigns with 160 independent runs per algorithm shows that, within the evaluated JSO/PSO family, RL-JSO is the only method that sustains a 100% collision-free rate across all four progressive difficulty campaigns, its Cliff’s delta over standard JSO grows monotonically with difficulty from medium to large, and under a composite cooperation metric its coordination score remains nearly invariant while comparators degrade by 17–23%. A paired inference-time ablation on the trained checkpoint provides controlled inference-time evidence that adaptive phase switching is a principal contributor to the observed test-time performance within the trained system, rather than the heuristic fallback layers. Full article

Total nitrogen (TN) is a critical indicator of water eutrophication. Conventional detection methods (e.g., alkaline potassium persulfate digestion and the Kjeldahl method) suffer from complex sample preparation, time-consuming operations, and reagent-induced pollution. Laser-induced breakdown spectroscopy (LIBS) offers unique advantages for rapid water quality analysis, yet it predominantly relies on costly actively Q-switched lasers, with passive Q-switching rarely explored due to multi-pulse output instability. This study employed a passively Q-switched laser as the excitation source for water TN measurement. By optimizing the multi-pulse trigger position, the signal-to-background ratio (SBR) was effectively enhanced. Combined with the substrate liquid–solid conversion method, key parameters (trigger delay, laser energy, argon flow rate) were optimized. Laboratory measurements of KNO₃ standard solutions (0–25 mg/L) using cyanogen (CN) molecular spectral lines yielded a coefficient of determination (R²) of 0.98, and a limit of detection (LoD) of 2.19 mg/L. Tests on actual water samples showed relative deviations ranging from 3.93% to 6.39%. These results demonstrate that passively Q-switched LIBS is a viable, cost-effective solution for rapid water nitrogen detection. Full article

We propose a 1D photonic crystal with nonlinear graphene–spacer–graphene truncation, which enables a tunable, non-monotonic, and intensity-dependent transmission response. By employing synthetic geometrical space to obtain Fermi arc states, the structure is designed to support a real-space topologically protected Tamm plasmon polariton, revealing an intensity-dependent transmission peak within the THz spectral range. As such, the proposed thin-film structure may serve as a nonlinear DBR element that can be integrated into a laser cavity to provide intensity-selective feedback, thereby facilitating controllable pulse shaping and enabling passive pulse formation mechanisms such as mode-locking or Q-switching. Due to its topological robustness, spectral scalability, and electrical tunability via graphene biasing, the platform provides a new route toward compact, reconfigurable nonlinear reflectors for efficient and controllable laser pulse generation, thereby extending the functionality of conventional saturable absorbers and semiconductor DBRs. Full article

Two-dimensional transition metal dichalcogenides (TMDs) are key materials in ultrafast photonics. However, the performance of conventional TMDs is limited by their bandwidth and carrier recovery time. The novel Dirac semimetal nickel ditelluride (NiTe₂), with its broad-band response and excellent nonlinear properties, emerges as an ideal candidate for saturable absorber (SA) materials. In this work, we report, for the first time, the application of NiTe₂ in the ytterbium-doped fiber laser, demonstrating stable passive Q-switching operation. The nonlinear transmission curve reveals a modulation depth of 6.82% at 1 µm and a saturation intensity of 2.12 MW/cm². Using an all-fiber ring cavity structure, stable Q-switched pulses with a central wavelength of 1031 nm were achieved at a pump threshold of 94 mW, with a maximum pulse repetition frequency of 30.1 kHz. The minimum pulse width reached 2.3 μs, and the single-pulse energy increased to 3.05 nJ, with an impressive radio frequency (RF) spectral signal-to-noise ratio (SNR) of 58.9 dB. This study demonstrates the potential of NiTe₂ as a high-performance SA in the near-infrared region, providing a solid foundation for its future application in ultrafast laser technologies. Full article

This work presents a direct conversion transmitter (DCT) for 5G new radio (NR) that eliminates the RF driver by directly feeding a single stage cascode PA through a baseband buffer amplifier and passive up-conversion mixer. The baseband interface uses Class-AB buffers to hold the output capacitor voltage, enabling accurate sampling at the PA input. A mixer switch is selected for minimal on-resistance variation over the required baseband swing. The PA is designed with separate I and Q voltage inputs and a current summing structure. The PA operates at 2.5 V; other blocks use 1.2 V. Post-layout two-tone simulations at 5 GHz indicate 21 dBm output saturation power and −36.1 dBc of IMD3 at 9 dB PBO power while removing the driver to inter stage matching network of a two-stage design. The results validate a compact, driverless architecture for integrated transmitters. Full article

To address the poor thermal performance and low output efficiency of conventional solid-state microchip lasers, this study proposes and implements a bonded Nd:YAG/Cr⁴⁺:YAG laser based on fiber splitter pumping. Experimental results demonstrate that at a 4.02 mJ pump pulse energy and a 100 Hz repetition rate, the system achieves four linearly polarized output beams with an average pulse energy of 0.964 mJ, a repetition rate of 100 Hz, and an optical-to-optical conversion efficiency of 23.98%. The energy distribution ratios for the upper-left, lower-left, upper-right, and lower-right beams are 22.61%, 24.46%, 25.50%, and 27.43%, with pulse widths of 2.184 ns, 2.193 ns, 2.205 ns, and 2.211 ns, respectively. As the optical axis distance increases, the far-field spot pattern transitions from a single circular profile to four fully separated spots, where the lower-right beam exhibits beam quality factors of M_x² = 1.181 and M_y² = 1.289. Simulations at a 293.15 K coolant temperature and a 4.02 mJ pump energy reveal that split pumping reduces the volume-averaged temperature rise in Nd:YAG by 28.81% compared to single-beam pumping (2.57 K vs. 3.61 K), decreases the peak temperature rise by 66.15% (6.97 K vs. 20.59 K), and suppresses peak-to-peak temperature variation by 78.6% (1.34 K vs. 6.26 K). Compared with existing multi-beam generation methods, the fiber splitter approach offers integrated advantages—including compact size, low cost, high energy utilization, superior beam quality, and elevated damage thresholds—and thus shows promising potential for automotive multi-point ignition, multi-beam single-photon counting LiDAR, and laser-induced breakdown spectroscopy (LIBS) online analysis. Full article

We describe the output characteristics of a compact, passively Q-switched, diode-end-pumped (Er/Yb):Glass laser operating in a multi-pulse burst mode. Such operation enables much higher optical efficiency and larger output of total energy than possible with conventional solitary pulse emissions. The laser generated a 15-pulse burst of pulses at 1.5 μm with a combined energy of 5.8 mJ. Measurements of pulse energies, spatial mode characteristics, output beam divergence, and impact of thermal effects in the (Er/Yb):Glass are described. These results are compared to predictions of a numerical simulation using a finite-difference beam propagation method (FD-BPM) that incorporates thermal effects caused by distributed local heating in the glass. We show good agreement between the measured and simulated laser output characteristics. Full article

We report a passively Q-switched self-Raman laser using a dual-end composite c-cut Nd:YVO₄ crystal, which generates switchable visible emissions at 533 nm, 560 nm, and 589 nm. A Cr⁴⁺:YAG/YAG composite crystal served the role of a saturable absorber to achieve passive Q-switching. An angle-tuned BBO crystal was used to achieve the frequency mixing between the first-tokes wave and the fundamental wave. At an incident pump power of 9.5 W, the maximum average output powers were 425 mW for the 589 nm yellow laser, 193 mW for the 560 nm lime laser, and 605 mW for the 533 nm green laser, with corresponding pulse widths of approximately 3.8, 3.6, and 35.1 ns, respectively. This result shows that a passive Q-switching operation with self-Raman crystals presents a promising approach for compact multi-wavelength pulse laser sources. Full article

We present a model of a Cr²⁺-doped saturable absorber (SA), which is employed in passively Q-switched (PQS) Tm:CaF₂ lasers. The overall round-trip loss, the time evolution of the intracavity photon density, and the effective population inversion density can all be obtained through numerical solutions. Under the mode-matching condition, this model can be used to easily determine the PQS laser’s main output parameters, including the average output power, repetition frequency, peak power, pulse energy, and pulse width. This concept is also applicable to a range of thulium-doped solid-state lasers (SSLs) operating on the transition from the ³F₄ level to the ³H₆ level, which are Q-switched by a Cr²⁺-doped SA. This model is helpful for the design and optimization of this kind of laser. 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

A passively Q-switched Thulium-doped fiber laser based on glycerin as the saturable absorber is experimentally demonstrated for the first time. The saturable absorber consists of two FC/PC connectors aligned within a mechanical fiber-fiber coupler, with the intervening gap filled with glycerin. Such a saturable absorber is integrated into a compact ring cavity, enabling passive Q-switched laser operation. Starting at a minimum pump power of 1.7 W, Q-switched pulses with a central wavelength of 1946 nm are obtained. At the maximum pump power of 2.4 W, the laser generates pulses with a duration of approximately 2 µs, a repetition rate of 26.7 kHz, and a pulse energy of 1.08 µJ. To the best of our knowledge, this is the first demonstration of passively Q-switched laser operation utilizing a glycerin-based saturable absorber for generating pulsed emission at the 2-µm wavelength region. This breakthrough represents a significant advancement in fiber laser technology, introducing a novel and efficient approach to pulse generation. Full article

Pulsed lasers have a wide range of applications in scientific and industrial fields, and the saturable absorber (SA) is the core device of pulsed lasers. Tungsten carbide (WC) has garnered significant attention due to its exceptional physicochemical properties, making it a promising candidate for optoelectronic applications, particularly as an SA in pulse lasers. This study is the first to report the nonlinear optical properties of WC thin film at a 1064 nm wavelength and its use as an SA device to generate pulsed lasers. A high damage threshold of 472.4 mJ/cm² was achieved, which is a critical parameter for high-power laser applications. The constructed laser demonstrated pulsed output with a central wavelength of 1064.12 nm, an average output power of 185 mW, and a narrow pulse width of 684 ns. Our research has provided a strong candidate for the development of future economically stable high-power laser systems. Full article